GB2249896A

GB2249896A - Automatic focusing

Info

Publication number: GB2249896A
Application number: GB9120686A
Authority: GB
Inventors: Chun-Gi Min; Su-Yeol Jeong
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1990-09-29
Filing date: 1991-09-27
Publication date: 1992-05-20
Anticipated expiration: 2011-09-27
Also published as: JPH04141634A; KR950008704B1; GB9120686D0; FR2668326B1; DE4131808A1; KR920007436A; JP2763828B2; DE4131808C2; GB2249896B; FR2668326A1

Description

1 2249896 AUTOMATIC FOCUSING APPARATUS AND METHOD FOR A VIDEO CAMERA The

present invention relates to an automatic focusing apparatus and method for a video camera, and particularly to an automatic focusing apparatus of a video camera and the method thereof, which can automatically adjust the focus of a video camera for a moving object.

In general, the automatic focusing methods of video cameras can be roughly classified into active types such as those using, for example, infrared ray distance measuring or ultrasound, and passive types such as those using image sensing and image detecting.

In particular, the principle of the active type using an infrared ray distance measuring procedure is shown in FIG.1, in which infrared rays are projected to an object to obtain the reflected distance measuring signal reflected by the object.

Referring to Fig. 1, the infrared light emitted from the light source of the infrared ray (not shown) such as an infrared light emitting diode (hereinafter, referred to as infrared LED) is directed onto the object 204 through the projecting lens 201, and the light reflected from the object 204 is focused on the light-receiving element 203 through the lightreceiving lens 202.

4 When L indicates the d1stance from the projecting lens 1 1 201 to the object 204, R indicates the distance from the projecting lens 2201 to the light-receiving lens 202, F is a focal length of the light- receiving lens 202, and X is the distance from the center of the light- receiving element 203 to the beam of infrared rays entering the light- receiving element 203 through the light-receiving lens 202, the relation between them is as follows:

F L = R ------- X Since the distance L between the projecting lens 201 and the object 204 is inversely proportional to the distance X between the center of the light-receiving element 203 and the incident point of the reflected light, the distance L can be determined.

Here, the lightreceiving element 203 is divided into two channels A and B, and the electrically equivalent circuit thereof is shown in FIG.2. In the drawings, when the P-sided electrodes are A and B and the N-sided electrode is C with reference to the structure of the light-receiving element, in is a total current amount produced proportional to the light incident position, V. is a driving voltage, D1 is an ideal diode, Cj is a junction capacitance, Rsh is a shunt resistor, R1 and R2 indicate resistors from the incident point of the reflected light to the electrodes A and B respectively, S is a current source, 2 W i i 1 and R is a load resistor.

Here, the photocurrents I, and 12 can be indicated as the following relation:

12 + It Rp + R k r According to the above equation Cp.,, the ratio of '12 - -LI M ( I:L + I, ), which is a ratio of the difference to the sum of the output currents, is proportional to the distance X from the middle point of the electrodes A and B, i.e., from the middle point of the light-receiving element to the incident point of the reflected light. That is, the incident angle or incident point of the beam of reflected infrared rays, which is a distance measuring signal on the light-receiving element, is changed according to the change of the distance between the object and the projecting apparatus.

Here, when the focusing of the object is correct, the reflected light enters the center of the light-receiving element, and the two converted currents I, and 12 are to be equivalent, so that the value of the equation 01. is zero. When the focusing is incorrect,the incident position of the ref I ected 1 i ght i s f ocused to be displaced to one s i de of the light-receiving elem-ent, so that the currents I, and 12 of both channels are different from each other, and the 3 equationT, has a value other than 0. Accordingly, if the AF motor is controlled to keep the linear relationship between the distance X from the center of the electrodes A and B to the incident point of the reflected light and the ratio of ( 12 It M 12 + Il), which is the ratio of the difference to the addition of the output currents, the exact focusing can be achieved.

Referring to FIG.3, after the infrared light generated from the infrared LED 1 of the light emitting part is projected to the object (not shown), the infrared light is reflected to enter the light-receiving element 2, and is converted to a photocurrent in the two channel electrodes A and B oil the light-receiving element 2, and is produced as an infinitesimal current signal. After the infinitesimal current signal is converted to a voltage signal in the first and second pre-amplifiers 3 provided in each channel, the output signals of the first and second pre-amplifiers 3 are filtered and amplified in the first and second synchronous filtering amplifier 4 to be synchronized to the synchronizing signal for turning on/off; the infrared LED.

in the first and second buffer amplifiers 5, after the output signals of the first and second synchronous filtering amplifier 4 are integrated, the noise component is removed and the signal level is raised to be output. At this time, when the outputs of the first and second buffer amplifiers 5 are signals A and B respectively, the A/D converter 6 4 1 i i i 1 receives the signals A and B, determines one of four cases (i. e., I A-B 1i 1_- Vd, A.a B, A+Bla Vh, A+B_> V P), and generates the determined result to the microcomputer 7. Here, Vd, Vh, and VP are respectively reference voltages for deciding the width of the responding range, the determining of the focusing, and the speed control range.

In the microcomputer 7, after the traveling direction and the speed or the stopping of the motor M which moves the photographing lens according to the combination of the four signals in the A/D converter 6 are determined, the speed control signal V and direction control signals F and B are supplied to the motor driver 10, and the motor M drives the photographing lens to an optimum focus position, thereby completing the automatic focusing.

Also, the microcomputer 7 supplies the clock signal CLK for making the infrared LED 1 turn on/off and detecting the synchronization of the lightreceiving signal to the first and second synchronous filtering amplifiers 4 and the infrared LED driver 9, and the clear signal CLR for clearing the charges of the integral-lion capacitor as a signal for determining the integration interval of the signal produced in the first and second synchronous filtering amplifiers 4, or for controlling the near distance limiter 8 not to control the focus for an object in the near distance, for example within 1 m.

During the position detecting, signals of channels A and B produced according to the incident position of the reflected light of the lightreceiving element are combined to a control signal in the A/D converter. To drive the AF motor requires an excessive amount of hardware; such as pre-amplifiers, synchronous filtering amplifiers, buffer amplifiers, etc., respectivel,i composed of two channels. There also arises another difficulty in that the A/D converter should be driven by low bias current and offset voltage as it is composed of ano-oerational amplifier. To reduce this nroblem, the amount of hardware has been further increased.

Moreover, since only the levels of both channel signals produced in the light-receiving element are detected and the combination signal in the A/D converter, composed of an operational amp] if ier controls the motor M, there arises a that -A'Ake focusing of the video camera can nolE, be carried out when the difference of both channel problem in precisely signals is small On the other hand, for an object disposed at a near distance or infinity for which the focusing is not needed, an additional near distance limiter 8 is installed or a stopper is provided on the driving part of the photographing lens, so that it results in a complicated constitution of the video camera.

6 i i J i 1 i i 1 i Therefore, it is an object of the present invention, to provide an automatic focusing apparatus of a video camera having a simple and highly reliable constitution to solve the above problems.

To achieve the above and other objects, an automatic focusing apparatus of a video camera according to the present invention comprises:

a light emitting part for emitting a light beam to measure a distance; a driver for driving the light emitting part; a light receiving part composed of' two channels, for producing photocurrent signals respectively corresponding to both channels - according to an incident point of reflected light which is projected from the light emitting part and is reflected by an object to be photographed; first and second current-voltage converting means for converting the photocurrent signals of both channels to amplified voltage signals respectively; a selector for selecting output signals of the first and second current- voltage converting means by time division; a filter for filtering the selected output signal; 7 an amplifying integrator for amplifying and integrating OUtpU4- signals of the detector, and outputting the integrated voltage signal; a comparing part for comparing the integrated voltage current with a reference voltage, and outputting a level signal according to the compared result; a motor driver for driving a focusing motor; and a microcomputer for sequentially receiving level signals corresponding to both channels of the comparing part, comparing the difference of level signals, and then driving the motor driver according to the difference of both level signals until two level signals are equal to each other.

Also, an automatic focusing method using a light emitting part for emitting measuring light beam and a light-receiving part of two channels for detecting a reflected light reflected from an object, comprises the steps of:

selecting one of the two channels and determining whether a detection signal of the selected channel is set to a predetermined reference voltage; selecting the other of the two channels and determining whether a detection signal of the other selected channel is set to the reference voltage or not; 8 i i i i i i locusing for long distance, when count values corresponding to the detection signals of the two channels are both above a"predetermined lower limit term, by stopping the focusing in case of the count value's being above a prescribed upper limit term and feeding back to the selecting step of one channel after focusing to infinite distance in case of the count value's being below the upper limit term; focusing for a proximate distance, when the count values corresponding to the detection signals of the two channels are both below the lower limit term and the two count values are not equal to each other, by rotating motor to proximate distance and feeding back to the selecting step of one channel when said count values are above the upper limit term; and controlling the light emitting part and direction and speed of focusing when the count values of the two channels are below the lower limit term and equal to each other.

The above objects and other advantages of the present invention will become more apparent by describing the preferred embodiment of the present invention with reference to the attached drawings, in which:

FIG.1 is a schematic view showing the principle of a conventional active type automatic focusing apparatus; 9 1 FIG.2 is an electric equivalent circuit diagram of a conventional light- receiving element; FIG.3 is a block diagram showing a conventional automatic focusing apparatus for a video camera; FIG.4 is a block diagram showing an automatic focusing apparatus for a video camera according to the present invention; FIG.5 is a circuit diagram of the automatic focusing apparatus for a video camera shown in FIG.4, in a preferred embodiment; FIG.6 is a view showing a frequency response characteristic curve of the band-pass filter shown in FIG.5; FIG.7A is a waveforms chart of the signal produced in the non-inverted amplifying circuit of the amplifying integrator shown in FIG.4; FIG.7B is a waveforms chart of the signal generated from the integrator of the amplifying integrator shown in FIG.4; FIG.7C is a waveforms chart of the driving signal for driving the infrared LED in the microcomputer shown in F IiG,. 4; FIG.8 is a detailed circuit diagram of the infrared LED 1 i i! i i shown in FIG.4; FIG.9 is a detailed circuit diagram of the motor driver shown FIG.4; FIG.10A is a schematic view showing the relationship between the power of the infrared LED driver and the count value of the microcomputer; FIG.10B is a schematic view showing the relationship between the motor controlling signal, and the voltage in a motor driver shown in FIG.9; and FIG.11 is a flow chart showing the processes for controlling the respective parts of the microcomputer shown in FIG.4 to drive the infrared LED and an AF motor, in which the drawing is divided into A to C for drawing convenience.

Hereinafter, a preferred embodiment of an automatic focusing apparatus of a video camera and the method thereof according to the present invention will be explained in more detail with reference to the attached drawings.

FIG.4 is a block diagram of an automatic focusing apparatus for a video camera according to the present invention.

Referring to FIG.4, in a light emitting part infrared rays are generated by using an infrared LED, example, and are projected through a projecting lens to 10, for an i i object to be photographed. The reflected infrared rays reflected from the object are focused at the light incident position on the light-receiving surface of a light-receiving part 20 through a light-receiving lens.

The lightreceiving part 20 consists of split lightreceiving elements of two channels A and B and converts the incident light to infinitesimal current signals I1 and 12. The first and second current-voltage converters, hereinafter referred to as I/V converters, 30 and 40 amplify the infinitesimal current signals I1 and 12 produced from the lightreceiving part 20 and generate corresponding voltage signals.

The selector 50 consisting of an analog switch sequentially and alternately selects the output signals of two channels A and B from the firsk and second I/V converters 30 and 40, and then supplies the selected output signals to the filter 60.

The filter 60 passes only the frequency components within a narrow band including a driving frequency of the infrared LED among the output signals of the channel selected by the selector 50, thereby improving the ratio of signal to noise S/N and then generates amplified signals.

The amplifying integrator 70 again amplifies the amplified and filtered signal in the filter 60 to be 12 converted to the corresponding current signal, and integrates the current signal to a voltage signal linearly increasing as time passes.

A comparator 80 compares the voltage signal supplied from the amplifying integrator 70 with a reference voltage, and outputs a level signal according to the compared result.

In a microcomputer 90, when the output signal of the comparator 80 is "low", a charging signal is transmitted to a capacitor of the amplifying integrator 70. And the reference clocks are counted from the start of the driving signal of the infrared LED, until the voltage signal produced in the amplifying integrator 70 reaches the reference voltage, to control the infrared LED driver 100 and the motor driver 110.

The infrared LED driver 100 receives a burst signal of a predetermined frequency from the microcomputer 90, and controls the intensity of the light emitted from the infrared LED, i.e., the power, in a plurality of steps, to make the infrared LED irradiate.

The motor driver 110 receives -- speed control signal V and direction control signals F and B according to the signal counted in the counter of the microcomputer 90, and drives the motor M.

FIG.5 is a detailed circuit diagram of the automatic 1:3 focusing apparatus of a video camera according to FIG.4.

In FIG.5, the light receiving element 20 generates an infinitesimal current proportional to the light intensity irradiated onto channels A and B, and supplies generated currents to the first and the second current-voltage converters 30 and 40 respectively.

However, when the picture is taken at a place where the ambient light is high, a direct current by the ambient light is produced in the lightreceiving element 20. Accordingly, the direct current signal supplied to the first and second I/V converters 30 and 40 is also increased, so that the level of the output voltage of the operation amplifier OP1 becomes lower, and the operation amplifier OP1 is and become negative.

saturated Thus, an ambient light removing circuit 31 is- provided to minimize the feedback impedance when the direct current flows, and selectively amplifies only the current generated by the burst signal from the microcomputer 90, for instance, by a 1OkHz alternating current signal.

In the ambient light removing circuit 31, when the output voltage Va of the operation amplifier OP1 is lowered to below -0.7V by increased direct current due to ambient light, a transistor TR1 is turned on to remove excessive current by resistors R33, R4 and a capacitor C2.

14 i j 1 i i When the direct current by the ambient light is removed in the ambient light current removing circuit 31, the output terminal of the operation amplifier OP1 of the first I/V converter 32 produces an amplified voltage signal, for instance, a signal having a gain of 50 dB. The high-pass filter 33 removes the noise of low frequency below 60 Hz among the output signals supplied from the output terminal of the operation amplifier OP1 by a capacitor C5 and a resistor R9, thereby producing a signal having an improved S/N ratio., As the constitution and the operation of the second I/V converter 40 is the same as the first IiV converter 30, the with the reference numerals in which 10 is commonly added to the reference numerals of the elements in the first I,(V converter 30, and the repetitive explanation is omitted.

corresponding elements are indicated The switch 50 alternately changes the output signals of the first and second I/V converters N and 40 with timedivision under the control of the microcomputer 90. The output signals of the I/V converters 30 and 40 selected by the switch 50 are filtered in the filter 60 to have a driving frequency of the infrared LED 10, for example, a frequency band having 10 kHz signal component only where wave detector 60 comprises an operation amplifier OP3, capacitors C7 and CS and resistors R11 and R12. The output signals of the I/V converter 30 and 40 are simultaneously amplified in filter 60 to have a gain, for instance, of 33 dB, and subsequently output.

The frequency response characteristic of the wave detector 60 is shown in FIG.6, in which the peak value 4 exists near at 27r ',.10 rad/sec. In this drawing, if the driving frequency of the infrared LED, i.e., 10 kHz of a burst signal is converted into the frequency unit of 4 rad/sec, 22r -.-'10 rad/sec is obtained, and the gain of 33 dB is obtained at this time.

In the non-inverted amplifying circuit 71 of the amplifying integrator 70, the output signal of the filter 60 is amplified to have a gain, for instance, of 13 dB, by the non-inverted amplifier OP4.

The voltage signal supplied from the output -11.erminal of the non-inverted amplifying circuit 71 will be indicated as Vp. In the integrator 72, when the output voltage signal Vp of the non-inverted amplifying circuit 71 is greater than the reference voltage, for instance, 2.5 V, the current value of Vp/R16 is supplied to the inverted terminal of the operation amplifier OP5, and accordingly the output of the operation amplifier OP5 becomes "low", and the transistor TR3 is turned on. Accordingly, the first switch SW1 is connected to the terminal of number 1, and the current value of Vp/R16 is charged in the capacitor C.

16 When the voltage V generated in the output terminal of the non-inverted amplifying circuit 71 is smaller than 2.5 V, the output of the operation amplifier OP5 becomes "high", so that the transistor TR3 is turned off, and the output' is clamped through the diode D1. At this time, when the object to be photographed is in a distance farther than the proximate distance, for instance, at 7 m, and the focusing is not correct, the signal amplified and produced in the non-inverted amplifying circuit 71 has such a waveform shown in FIG.7A. And, the signal obtained from the output signal of the non-inverted amplifying circuit 71 by being charged and integrated in the capacitor C of the integrator 721 has such a waveform shown in FIG.7B. Here, when the wave 0 I - non-inverted amplitude ol the output signal of the amplifying circuit 71 is larger, larger currents flow in the capacitor of the integrator 72, thereby more rapidly reaching the reference voltage. Accordingly, the voltage difference of two channels A and B selected alternately by the switch 50 can be converted into the time difference of the integrated signal. That is, a proportional relationship exists in both terms, which is (Va-Vb) cc (tb-ta).

Accordingly, the microcomputer 90 counts the reference clock, and operates the difference of these integration times ta and tb, thereby determining whether the focusing is carried out and determining the control degree.

on the other hand, when the integration voltage 17 j 1 integrated by being charged in the capacitor C of the integrator 742 in the comparator 80 is greater than the reference voltage Vcc set in positive terminal of the differential amplifier OP6, the output level of the differential amplifier OP6 is set to "low", and is supplied to the microcomputer 90.

Accordingly, the microcomputer 90 transmits a discharging signal to discharge the charge in the capacitor C through the discharge.resistor R, thereby clearing the integrator 72.

FIG.7C is a waveforms chart of the burst signal, which is 10 kHz driving frequency of infrared LED supplied from the microcomputer 90. For instance, if the period of the burst signal is 100 AL sec and the infrared LED is irradiated for 40 msec and the motor is controlled for 30 msec, the sampling period of the apparatus according to the present invention is 70 msec.

FIG.8 is a detailed circuit of the infrared LED driver 100 shown in FIG.4. Referring to FIG.8, the driving signal supplied from the microcomputer 90, i.e., a 10 kHz burst signal IR is supplied to the transistor TR4 of the infrared LED on/off circuit 101. On the other hand, the microcomputer 90 counts the amplitude of the output signal of both channels A and B set as "low" levels in the comparator 80, and divides the signal into light intensity control signals 18 1 P1, P2, P3 and P4 of four steps to be supplied to the infrared LED driver 100. In the infrared LED irradiating intensity controlling circuit 102, when a "high" signal is supplied from the microcomputer 90 to the terminal P1, the transistors TR7 and TR8 connected with the darlington connection are turned on, so that the current il flows, and the light intensity of the infrared LED 10 is controlled to the intensity corresponding to the current il, and the infrared LED is irradiated.

When a "high" signal is supplied from the microcomputer 90 to the terminal P2, the transistors TR9 and TR10 connected with the darlington connection are turned on, and the infrared LED 10 is irradiated with the intensity corresponding to the current il + i2. When a "high" signal is supplied from the microcomputer 90 to the terminal P3, the transistors TR11 and TR12 connected with the darlington connection are turned on and the infrared LED 10 is irradiated with the intensity corresponding to the current il+i2+i3. When a "high" signal is supplied from the microcomputer 90 to the terminal P3, the transistors TR13 and TR14 connected with the darlington connection are turned on, the infrared LED 10 is irradiated with the light intensity corresponding to the current il+i2+i3+i4.

FIG.10A is a schematic view showing the relationship between the light intensity for driving the infrared LED in the driving circuit shown in FIG.8 and the count value being 19 calculated in the microcomputer. In this drawing, the count value of the microcomputer and the light intensity control signal are respectively indicated in the dimensionless unit. The reason of controlling the light intensity in a plurality of steps is that the reflected light intensity received in the light receiving element is changed according to the kind of the object to be photographed or the distance, so that a compensation is needed to get a signal having a constant level. That is, when the microcomputer count value corresponding to the integration time difference between two channel signals becomes larger, the infrared LED should be driven to the large light intensity, and when the reflectivity of the object is low, the infrared LED should be driven with the large light intensity. At this time, since the total gain of the automatic focusing apparatus of the above-mentioned preferred embodiment is about 100 dB, for example, the light intensity of the infrared LED, ie., the driving voltage, is controlled in four steps Go constantly have a dynamic range regardless of the type of the object and its distance.

FIG.9 is a detailed circuit diagram of the motor driver 110 shown in FIG. 4.

Referring to FIG.9, the motor driver 110 includes a motor direction control circuit 111 and a motor speed control circuit 112. Here, in the motor direction control i i 1 circuit 111, the rotation direction of the motor is decided by the signal counted in the microcomputer 90. For instance, when the control signal of the positive direction is supplied as a "high" signal to a positive direction terminal P.DIRECTION in the microcomputer 90, the control signal directs the motor to rotate to the positive direction through transistors TR-20, TR22), and TR19.

On the other hand, when a control signal of a negative direction is supplied to a negative direction terminal N.DIRECTION as a "high" signal, the control signal directs the motor to rotate to the negative direction through transistors TR21, TR-233, and TR18.

Also, if the signal difference between two channels A and B, i.e., the count value difference, is large, the motor is preferably controlled at a high speed. On the other hand, as a motor has the inertia, and the hunting is easily generated, the motor should be controlled at a low speed when the signal difference between two channels A and B is small.

Accordingly, if the signal difference between both channels A and B is small, a "high" signal is supplied as a low speed control signal to a low speed terminal LOW SPEED of the motor speed control circuit 112 from the microcomputer 90, so-that the transistor TR15 is turned on and the motor is rotated at a low speed to avoid the 21 j hunti ng.

In the motor direction and speed control, the control is carried out by a pulse width modulated (PWM) signal from constant voltage fed according to the counted signal in the microcomputer 90. In the control signals indicated with vertical dots in FIG.10B, the control signals in the further right side have larger pulse widths, so that the driving speed of the motor becomes faster.

FIGS.11A to 11C are flow charts showing the processes in which each part is controlled in the microcomputer shown in FIG.4, to drive the infrared LED and AF motor, and will be explained with reference to FIGS. 4 to 9.

In a step S1, after the microcomputer 90 is initialized to clear the memory and counters, a capacitor C of the i n-lz,-e- grator 72 is discharged for 1 msec, and a light intensity control signal P4 is first selected for a maximum powe r.

In steps S2 and S3, after the infinitesimal current signals I1 and 12 produced in the light-receiving element 20 are converted to voltage signals in the first and the second I/V converters 30 and 40, a control signal is supplied to the switch 50 to select the channel A (in the step S2), and the signal transmitted to the channel A is charged and integrated in the amplifying integrator 70 via the filter 60 (in the step S3). 22 In steps S4 and S5, the 10 kHz burst signal for driving the infrared

LED is turned on, for instance, for 50 1,1 sec and at the same time the counter is turned on (in the step G4), and the burst signal is turned off for 50 a sec, thereby producing a driving signal of the infrared LED having a period of 100 m sec (in the step S5).

In the steps S6 to S8, the microcomputer determines whether the integration signal of the channel A transmitted to the comparator 80 is set to a reference voltage or not (in the step S6). If the signal is set, the number of burst signals is stored in the counter from the start of driving the infrared LED until the signal of the channel A is set (in the step S7), and a clear signal for discharging the capacitor c of the integrator 72 is produced (in the step S8).

In a step S9, if the signal of the channel A is not', set in the step S6, the microcomputer checks whether the number of the counted burst signal is larger than 200 or not. If the number is larger than 200, the step S7 is carried out, and if not, the procedure is fed-back to the step S4. Here, the burst signal count number 200 corresponds to the value of 20 msec, which is the bottom limit value for the case of object's being at the proximate distance or stopping of integration by noise.

23 In steps S10 to S11, a control signal is sent to the switch to select the channel B (in the step S10), and the signal transmitted through the channel B is charged in the capacitor C of the integrator 72 to be integrated (in the step S11).

In steps S12 and S13, after the 10 kHz burst signal for driving the infrared LED is turned on for 50 jA sec and the counter is turned on (in the step S12), the burst signal is turned off for 50 1-tsec, thereby producing the driving signal of the infrared LED having a period of 100 ft sec (in the step S13).

In steps S14 and S16, it is determined whether the integration signal of the channel B, transmitted to the comparator 80 is set to a reference voltage or not (in the step S14), and if the signal is set, the number of burst signals is stored in the counter from the start of driving the infrared LED until the signal-of the channel B is set (in the step S15), and a clear signal for discharging the capacitor C of the integrator 72 is produced (in the step S16).

In a step S17, if the integration signal of the channel B, transmitted to the comparator 80 is not set in the step S14, it is determined whether the number of the burst signals is larger than 200 or not, and if it is larger than 200, the step S15 is carried out, and if not, the procedure 24 i i is fed-back to the step S12.

In steps S18 to S21, it is determined whether each of the count values of the channels A and B is above the lower limit term, i.e., above 20 msec (in the step S18), and if it is above 20 msec, it is discriminated whether the count value is above 10 sec or not (in the step S19), and if it is above 10 sec, the photographing lens is considered to be moved to a infinite position, the motor is stopped (in the step S-20), and if not, the motor is rotated to the infinity direction to be fed-back to the step G2 (in the step S21).

In the steps S22 to S24, if the count values of the channels A and 9 in the step S18 are below 20 msec respectively, it is determined whether the count values of the channels A and B are equal to each other or not (in the step S22). If they are not equal, it is again determined whether the count value is above 10 sec or not (in the step G23). If it is above 10 sec, the photographing lens is considered to be moved to a proximate position, and the motor is stopped (in the step S24). If the count value is below 10 sec, the motor is rotated to the proximate direction and then the procedure is fed-back to the step S2 (in the step S24).

In steps S25 to S28, when the count values A' and B' of the channels A and B in the step S22 are almost equal to each other, i.e., when the amplitudes of the position detecting signals of the channels A and B are almost equal to each other, the amplitudes of the signals transmitted to channels are proportional to the inverse numbers of the count values A' and B'. Accordingly, the amplitude difference is equal to the ratio of (B'A')/(A'B') which is the ratio of the difference to the product of the count values, and this value is stored in the register R5 (in the step S25). And the sum of the amplitudes corresponds to the ratio of W+A')/MB', which is the ratio of the sum to the product of the count values, is stored in the register R4 (in the step S26). The ratio of the value stored in the register R5 to the value stored in the register R4, i.e., the ratio of (B'-A')/(B'+A'), which is the ratio of difference and the sum of the count values is stored in register R3 (in the step S27), and the power of infrared LED is selected according to the stored value the register R4 ( in the step S28).

the the the i n As shown in FIG.10A, the farther the object whose distance is measured is, the larger the count value is, and accordingly the required light- irradiation intensity, i.e., the power, of the infrared LED is increased. Therefore, in the present invention, the light emitting intensity of the infrared LED is divided and controlled in four steps according to the count value, and the leading and trailing edges of each step are overlapped to each other whenever the step is changed in order to stabilize the system. This 26 overlapped portion corresponds to a hysteresis band.

In steps S29 to S31, it is checked whether the order change, i.e., a carry, of the stored value in the register R5 is generated or not (in step S29), and if the carry is generated, the motor is moved to the negative direction (in the step S30), and if not, the motor is moved to the positive direction (in the step S11).

In steps S32 and S33, the ratio of W-A')/W+A'), which is the ratio of the difference and the sum of the counter values stored in the register R3 is compared with a predetermined error value c representing the hysteresis band (in the step S32), and when it is below the error value, the motor is stopped, the automatic focusing is completed, and fed back to the step S2 (in the step S33). At this time, the error value c is set to a value below 5% of the stored value in R3, for instance.

In steps S34 to S37, when the value stored in the register R3 from the step S32 is above the error value c, it is determined whether the value stored in the register R3 is above a set value K for the low speed driving (in the step S34), and if the value is above the set value K, the motor M is controlled to rotate at a high speed by a pulse width modulation PWM (in the steps S35 and S37), and if the value is below the set value K, the focusing is carried out by controlling the motor to rotate at a low speed and then 27 fed back to the step S2 (in the steps S36 and S37). At this time, the set value K is set to the value of 20 % of the stored value in the register R3, for instance.

As described above, according to the present invention, the infinitesimal currents of two channels generated from the light-receiving part is processed by onechannel, thereby simplifying the constitution. Moreover, the control signal for driving the infrared LED and AF motor is processed with software in a microcomputer, so that the difficulty of keeping low bias current and the small off set voltage characteristic required for hardware implementation is solved and the reliability and the stabilization of the system are increased.

The invention being thus described it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the invention.

There are described above novel features which the skilled man will appreciate give rise to advantages. These are each independent aspects of the invention to be covered by the present application, irrespective of whether or not they are included within the scope of the following claims.

28 A 1

Claims

1. An automatic focusing apparatus for a video camera comprising:

a light emitting device for emitting a light beam to measure a distance; a driver for driving said light emitting device; a light receiving device composed of two channels, for producing photocurrent signals respectively corresponding to the two channels according to an incident point of reflected light projected from said light emitting device and reflected by an object; first and second current-voltage converting means for converting each photocurrent signals of the two channels to an amplified voltage signal; a selector for selecting output signals of said first and second current- voltage converters by time-division; a filter for filtering said selected output signal; an amplifying integrator for amplifying and integrating output signals of said filter; means for comparing an integrated voltage signal with a set voltage, and generating a level signal according to a nnmnared result; 29 a motor driver for driving a focus controlling motor and a microcomputer for sequentially receiving level signals of said comparing means corresponding to said two channels, comparing the difference, and driving said motor driver according to said difference of said two level signals until said two level signals are equal to each other.

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2. An automatic focusing apparatus for a video camera as claimed in claim 1, wherein each of said first and second current-voltage converting means comprises:

first and second ambient light current removing circuits for removing the effect of an ambient light; first and second current-voltage converters for converting the photocurrent signal generated from said light-receiving device to a voltage signal; and 1 a highpass filter for removing noises of signals supplied from said first and second current-voltage converters.

3. An automatic focusing apparatus for a video camera as claimed in claim 2, wherein each of said first and second ambient light current removing circuits comprises:

1 1 1 transistors for respectively turning on when direct current by said ambient light is supplied to each collector terminal; resistors and capacitors, for removing excessive direct currents when said transistors are turned on.

4. An automatic focusing apparatus for a video camera as claimed in claim 1, wherein said selector receives control signals from said microcomputer and sequentially selects the output signals of said two channels responsive to the control signals for a predetermined sampling period.

5. An automatic focusing apparatus for a video camera as claimed in claim 4, wherein said selector consists of an analog switch.

6. An automatic focusing apparatus for a video camera as claimed in claim 2, wherein said filter comprises a bandpass filter consisting of an operational amplifier, resistors and capacitors, which filters signal components having a predetermined frequency among signals output from the respective high-pass filters of said first and second current-voltage converters and amplifies the filtered signal components.

7. An automatic focusing apparatus for a video camera as claimed in claim 1, wherein the amplifying integrator comprises:

31 a non-inverted amplifying circuit for non-inverted amplifying the signals filtered in said filter; and an integrator for integrating an input signal when the signal supplied from said non-inverted amplifying circuit is greater than a predetermined reference voltage, and for clamping an input signal when an output signal of said noninverted amplifying circuit is smaller than said reference voltage.

8. An automatic focusing apparatus for a video camera as claimed in claim 1, wherein said means comprises a comparator which is set to predetermined level when said amplifying integrator obtains a predetermined voltage level or more as a result value.

9. An automatic focusing apparatus for a video camera as claimed in claim 1, wherein said microcomputer produces:

a burst signal for driving said light emitting device; a control signal of said amplifying integrator according to said level signal supplied from said means for comparing; and control signals of said driver and motor driver calculated by converting position detection signals of the two channels output according to the position of the reflected light entering the two channels into count value.

10. An automatic focusing apparatus for a video camera 32 1 as claimed in claim 1 ' wherein said driver comprises:

an infrared LED on/off circuit for turning on/off said light emitting device according to a burst signal of a predetermined frequency supplied from said microcomputer; an infrared LED irradiation intensity control circuit for receiving the control signal from said microcomputer to determine the light intensity of said light emitting device.

11. An'automatic focusing apparatus for a video camera as claimed in claim 10, wherein the control signal of said microcomputer controls said infrared LED irradiation intensity control circuit in power levels oil four steps.

121. An automatic focusing apparatus for a video camera as claimed in claim 1, wherein said driver receives control signals from said microcomputer, then controls said light emitting device in levels of predetermined steps.

13. An automatic focusing apparatus for a video camera as claimed in claim 1, wherein said motor driver comprises:

a motor direction control circuit for controlling a rotation direction of said motor; and a motor speed control circuit for controlling a rotation speed of said motor.

14. An automatic focusing apparatus for a video camera 33 i as claimed in claim 13, wherein said motor direction control circuit comprises a plurality of transistors and resistors having an H bridge structure, thereby controlling the rotation direction of said motor according to control signals supplied from said microcomputer.

15. An automatic focusing apparatus for a video camera as claimed in claim 13, wherein said motor speed control circuit comprises a plurality of transistors, resistors, and a diode, thereby controlling speed of said motor at a low speed when a low speed control signal of said microcomputer is supplied to a low speed terminal.

16. An automatic focusing apparatus for a video camera as claimed in claim 45, wherein said control signal supplied from said microcomputer is a pulse width modulated signal.

17. An automatic focusing method for a video camera, using a light emitting device for emitting a measuring light beam and a lightreceiving device of two channels for detecting a reflected light reflected from an object to be photographed, comprising the steps of:

selecting one of' the two channels and determining whether a detection signal of said selected channel is set to a predetermined reference voltage; selecting the other of said two channels and determining whether a detection signal of the other selected 34 channel is set to the reference voltage or not; focusing for long distance, when count values corresponding to the detection signals of said two channels are above a predetermined lower limit term, by stopping focusing where the count value is above a prescribed upper limit term and feeding back to the selecting step of one channel after focusing to infinite distance where the count value is below said upper limit term; C locusing for proximate distance, when the count values corresponding to the detection signals of the two channels are both below the lower limit term and the two count values are not equal to each other, by rotating the motor to proximate direction and feeding back to said selecting step of one channel where the count value is above the upper limit term; and controlling said light emitting devices and, direction and speed of focusing when the count values of the two channels are below the lower limit term and equal to each other.

18. An automatic focusing method for a video camera comprising the steps of:

projecting an infrared light to an object whose distance is to be measured by an infrared LED; receiving a reflected light reflected from said object j 5 via two channels, and generating photocurrent signals corresponding to the received light; converting said photocurrent signals to voltage signals; ampl if ied sequentially selecting signals supplied from said current-voltage converting step; filtering signals selected from said selecting step; amplifying signals supplied from said filtering step, and integrating the amplified signals; comparing signals fed from said amplifying and integrating step with a predetermi-ned reference voltage to produce a level signal according to the compared result; generating control signals driving said infrared LED and said motor by converting integral-led signals from said amplifying and integrating step into count values according to said level signal from said comparing step; driving said infrared LED according to said control signal; and driving said motor according to said control signal.

19. An automatic focusing method for a video camera as claimed in claim 18, wherein in said infrared LED driving Step, light emitting intensity of said infrared LED is 36 j 1 driven in predetermined steps according to said count val ue.

20. An automatic focusing method for a video camera as claimed in claim 18, wherein said motor driving step controls rotation direction and speed of said motor by a pulse width modulated signal according to said count value.

21. An automatic focusing apparatus for a video camera as claimed in claim 22, wherein said filter includes an operation amplifier and a high pass filter consisting of resistors and capacitors.

22. An automatic focusing apparatus for a video camera as claimed in claim 14, wherein said control signal supplied from said microcomputer is a pulse width modulated signal.

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23. Automatic focusing apparatus for a video camera comprising focusing means and a two-channel photosensitive detector operable to generate two signals whose relative magnitudes are representative of the displacement of the focusing means from the correct focus position, and wherein means are provided f or consecutive processing of said two signals to derive drive signals to drive the focus means towards the correct focus position.

24. An automatic focusing apparatus for a video camera substantially as herein described with reference to figures 4 to 11 of the accompanying drawings.

25. An automatic focusing method for a video.camera substantailly as herein described with reference to figures 4 to 11 of the accompanying drawings.

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