INFRARED REPEATER The present invention relates to an infrared repeater, and more specifically, to an infrared repeater that remains operational in the presence of interference caused by compact fluorescent lights. Current wireless remote control units for consumer electronic equipment, such as television receivers, video tape recorders, and satellite or cable receiver boxes, operate by transmitting an infrared (IR) signal, representing an encoded signal modulated in a modulating signal, from the remote control unit to the consumer electronic equipment. This modulated IR light signal is received by an IR receiver in the consumer electronic equipment, demodulated, decoded, and the appropriate action is carried out. The IR remote control units are line of sight devices, meaning that any consumer electronic equipment that is in shadow with respect to the IR light generated by the remote control unit will not be able to receive the IR light signal and respond to the order. In addition, the IR remote control units have a limited operational range, which is sufficient for use within a room, but is not sufficient for use between rooms. However, currently, electronic consumer equipment is being placed inside furniture, such as home entertainment units, behind solid doors. For example, a television, cable box, satellite receiver, etc. , they can be placed in a home entertainment unit in such a way that, although the television receiver is visible to the viewer, the cable box, the satellite receiver and the video tape recorder are placed behind solid doors. In addition, electronic consumer equipment is being distributed among different rooms in a home. For example, a satellite receiver may be located next to a television receiver in a family room, but may also be coupled to a second television receiver in a bedroom. The I R light generated by the remote control units can not penetrate through solid doors or move from room to room, so that equipment hidden or remotely located can not be controlled. To provide the ability to control electronic consumer equipment within cabinets or in different rooms of a home, IR repeaters have been developed. An I R repeater includes an IR receiver section located where it can receive the encoded modulated IR signal generated by the remote control unit. For example, it may be located outside of an entertainment unit or in the room in which the remote control unit is being used. The receiver section I R is connected to an IR transmitting section located where the consumer electronic equipment that is to be controlled can receive its signal. For example, it is located inside the entertainment unit or in the room in which electronic consumer equipment is located. The transmitter section I R includes an IR light emitter which is positioned so that the light I R emitted hits the receiver I R in the consumer electronic equipment to be controlled. More specifically, the light emitter I R is usually placed directly adjacent to the IR receiver in the consumer electronic equipment. The receiver section I R of the repeater I R detects the encoded light signals I R produced by the remote control unit and transmits them to the IR transmitting section, usually by means of a cable. The IR transmitting section generates an IR light signal which is identical to the light signal I R received by the receiver section I R. The consumer electronic equipment receives this light signal I R from the transmitter section I R, and performs the desired function. Different manufacturers of consumer electronic equipment use different modulating frequencies to modulate the control signal encoded in the I R light signal. For the I R repeaters to work with the respective modulation frequencies of the manufacturers, I R repeaters use an I R detector in the IR receiver section that has a relative frequency bandwidth response characteristic. That is, it will detect modulated I R light signals for which the modulation frequency can vary over a relatively wide range of frequencies. For example, I R repeaters can generally detect I R light signals that are modulated at any modulating frequency of approximately 20 kilohertz (kHz) to 100 kHz. Any IR signal modulated in this frequency range can be detected by the IR receiver, and when it is detected, an IR signal is generated imitating the signal received in the I R transmitter. Recently the fluorescent lights have ballasts, called compact fluorescent lights ( CFLs), have been developed as a replacement for incandescent lights. Compact fluorescent lights use less energy than incandescent lights, and have become popular for that reason. However, compact fluorescent lights produce I R light that has characteristics similar to those of encoded modulated IR light signals produced by remote control units. That is, the electronic ballast in a compact fluorescent light causes the fluorescent tube to produce I R light signals that appear to be modulated by a modulation frequency in the range of 20 to 100 kHz, and specifically by a frequency of approximately 56 kHz. In addition, the I R light produced by compact fluorescent lights has a much higher intensity than that produced by remote control units. Thus, the light I R produced by a compact fluorescent light completely conceals the modulated encoded I R receiver section produced by a remote control unit. Because the current I R repeaters mimic the signal I R received by its receiver section, any interference from nearby compact fluorescent lights collected by the IR repeater is also mimicked by the light signal I R produced by the I R repeater. It has been found that, in the presence of compact fluorescent lights, repeaters have seriously degraded their operation or even become completely inoperative. IR detectors have been developed and are resistant to interference caused by compact fluorescent lights. These detectors can receive an IR light signal by representing a modulated coded control signal from a remote control unit in the presence of interference light of a compact fluorescent light and, in a known manner, cancel the interference of the compact fluorescent light. . The modulated coded IR light signal from the remote control unit is then demodulated, and such that an IR detector produces an electrical signal representing the coded control signal. An IR repeater that can operate with remote control units from various manufacturers, and that can operate reliably in the presence of compact fluorescent lights, is desirable. In accordance with the principles of the present invention, an IR repeater, resistant to the interference of compact fluorescent lights, includes a receiver section for receiving an IR light signal representing a coded signal modulated by a modulation signal, and for detecting the signal encoded An oscillator generates a modulating signal of the transmitter and a transmitting section generates an IR light signal representing the detected encoded signal modulated by the modulating signal of the transmitter. If an IR detector resistant to compact fluorescent lights is used in the receiving section, the effect of compact fluorescent lights can be minimized, and the operation of the receiving portion will not be seriously degraded by compact fluorescent lights. The receiving section is tuned to respond to a frequency of the center of the modulating signal approximately in the middle of the frequency range used by the respective manufacturers, and the frequency of the modulation signal produced by the oscillator is also approximately in the middle of that frequency range. Because the frequency of the modulating signal in the IR signal produced by the transmitting section of the IR repeater is approximately half the frequency range used by the respective manufacturers, it can be detected by the IR receivers in the consumer electronic equipment. any of those manufacturers. In addition, the modulating signal of the transmitter is a clean signal produced by an oscillator in the repeater, not imitated from the receiving section. Thus, the signal produced by an IR repeater according to the present invention will produce a clean IR light signal modulated, free of interference from compact fluorescent lights. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a block diagram illustrating a remote control system including an IR repeater, in accordance with the present invention; Figure 2 is a waveform diagram useful in understanding the operation of the present invention; Figure 3 is a schematic diagram illustrating in more detail the repeater I R illustrated in Figure 1; and Figure 4 is a schematic diagram illustrating an alternative embodiment for an IR detector illustrated in Figure 3. In Figure 1, a remote control unit 10 provides coded control signals modulated in an IR light signal to a detector. of IR light 25 of an IR receiving section 20 of a repeater I R. In the IR repeater of Figure 1, the IR light detector 25 is illustrated as an IR phototransistor, although any IR light detecting device can be used. A control output terminal of the IR receiving section 20 is coupled to a control input terminal of a signal gate 30. A fixed frequency oscillator 40 has a signal output terminal coupled to a signal input terminal of the signal port 30. A signal output terminal of the signal port 30 is coupled to an input terminal of an IR transmitting section 50 of the IR repeater. The transmitting section IR 50 is coupled to an IR light emitter 55 which produces an IR light signal corresponding to the electrical signal received at the input terminal corresponding to the transmitting section IR 50. In the IR repeater of Figure 1, the IR light emitter is illustrated as an IR light emitting diode (LED), although any IR light emitting device can be used. This IR light emitter 55 is positioned in such a way that the emitted IR light hits an IR light detector 65 of a piece of consumer electronic equipment 60. In Figure 1, the IR light detector 65 is illustrated as a phototransistor IR, although any IR light detector device can be used. In addition, consumer electronic equipment 60 is illustrated as a television receiver, although the IR repeater of Figure 1 will work with any consumer electronic equipment that can be controlled remotely by an IR remote control unit. In operation, the remote control unit 10 produces a coded modulated IR light signal. In the illustrated embodiment, the encoded signal (described in more detail below) is a modulated pulse code signal (PCM) representing an order for the television receiver 60. This signal is detected by the IR phototransistor 25, which generates a electrical signal representing the encoded modulated signal, and supplying that signal to the receiving section IR 20. The IR receiving section 20 demodulates the electrical signal of the IR light sensor 25, and produces a two-state signal representing the pulses that make up the modulated signal of pulse code. This signal has a first state representing the presence of the modulated IR light in the IR phototransistor 25, for example, a logic signal "1"; and a second state representing the absence of the IR light modulated in the IR phototransistor 25, for example, a logic signal "0". This signal is supplied to the control input terminal of the signal gate 30. The fixed frequency oscillator 40 produces a modulation signal having a frequency of approximately 47 kHz at its output terminal. This frequency is selected to be close to the middle of the frequency range (from about 32 kHz to about 56 kHz) used by the respective manufacturers to modulate their modulated pulse code signals in the IR light signal of their control units remote. This modulation signal is supplied to the data input terminal of the signal port 30. The signal port 30 operates as a controllable switch. When the signal of the IR receiving section 20 is a logic signal "1" (representing the presence of the IR light modulated in the IR phototransistor 25), the signal gate 30 is conditioned to pass the modulating signal at its input terminal signal to your output terminal. When the signal from the IR receiving section 20 is a logic signal "0" (representing the absence of the IR light modulated in the IR phototransistor 25), the signal port 30 is conditioned to block the modulating signal at its input terminal. The output signal of the signal gate 30 is an electrical signal representing the received encoded signal modulated in a modulation signal of 47 kHz. The signal from the signal gate 30 is supplied to the transmitting section IR 50. The transmitting section IR 50 conditions this signal to drive the light emitting diode IR 55 so as to produce an IR light signal corresponding to this modulated signal. Thus, the IR light signal produced by the light emitting diode IR 55 is the pulse coded signal received by the IR phototransistor 25, but modulated in a modulating signal of 47 kHz. This encoded modulated IR light signal strikes the IR phototransistor 65 in the television receiver 65. The television receiver 60 responds in the normal manner to the encoded, modulated IR light signal received by performing the command represented by that signal encoded Figure 2 is a waveform diagram useful in understanding the operation of the present invention. The waveforms illustrated in Figure 2 represent the encoded modulated signals produced by the remote control unit 10 (of Figure 1) and by the light emitting diode IR 55 of the IR repeater. The differences between the signals produced by these respective sources will be described below. In Figure 2, a series of code pulses is illustrated. In Figure 2a, the pulses are arranged to form a coded pulse position signal. A series of clock pulses C1, C2, C3, ... are produced with data pulses D1, D2, ... interposed between them. The time position of the data pulses D1, D2, ... between the clock pulses C1, C2, C3, ... determines if a logic "1" or "0" is being transmitted during the interval between the pulses of successive clock C1, C2, C3.
With reference to the clock pulses C1 and C2 and the data pulse D1, the data pulse D1 is closer in time to the clock pulse C1 than to the clock pulse C2. This represents a data bit having a logic value "1" Referring now to the clock pulses C2 and C3 and to the data pulse D2, the data pulse D2 is closer in time to the clock pulse C3 than to the pulse of clock C2. This represents a data bit that has a logical value "0". If the first pulse of data had been transmitted in the alternative time D1 a, it would have been represented as a data bit with a logical value "0", and if the second pulse of data had been transmitted in the alternative time D2a, it would have been represented as a data bit with a logical value "1". A control signal comprises a predetermined number of data bits. Figure 2b illustrates in more detail the composition of the clock pulse C2 illustrated in Figure 2a. Each pulse illustrated in Figure 2a has a predetermined pulse width, and is composed of pulses of IR light occurring at the modulation frequency. In Figure 2b, the shaded areas represent the presence of light I R, and the blank areas represent a lack of IR light. The envelope of the IR light pulses, repeating at the modulation frequency, defines the data and clock pulses illustrated in Figure 2a. For the modulated coded pulses produced by the remote control unit 10 (of Figure 1), the modulation frequency is that used by the manufacturer of the remote control unit 10 (ranging from about 32 kHz to about 56 kHz). For the modulated coded pulses produced by the light emitting diode I R 55 of the transmitter section 50 of the I R repeater, the modulating frequency is selected to be approximately 47 kHz.
Referring again to FIG. 1, as described above, the light receiving section I R 20 is designed to detect and minimize the effects of parasitic IR light emitted by compact fluorescent lights. The light I R emitted by the compact fluorescent lights consists of successive groups of pulses of light I R having a frequency between approximately 20 and 100 kHz. The pulses of light have envelopes defined by the AC energy supplied to the compact fluorescent light. Within each half cycle of the AC energy, the compact fluorescent light produces a set of pulses of light I R. The envelopes of the groups have a duty cycle of approximately 50%, and the groups occur at a frequency of about double the AC power frequency. Specifically, it has been found that one type of compact fluorescent light produces pulses of IR light at approximately 56 kHz, with envelopes having a repetition frequency in the United States of 120 Hz and a duty cycle of 40%. The characteristics of these pulses are sufficiently different from those of the pulses illustrated in Figure 2b, so that the receiver section I R 20 is capable of detecting pulses of light I R having these characteristics and canceling or minimizing their effect. As described above, the encoded modulated light signal I R produced by the light emitting diode I R 55 of the transmitter section I R 50 may have a modulatory frequency slightly different from that expected by the television receiver 60.
However, in an IR repeater application, this is not a problem. A remote control unit 10 operates with battery power and therefore produces IR light at a relatively low energy level. In addition, a remote control unit is generally operated at a relatively large distance from the television receiver, for example, in the order of several meters away. The light receiver I R in the television receiver is sensitive enough to detect the IR light signals produced under these circumstances. But the I R repeaters are generally coupled directly to the household AC power source and, therefore, they can produce light I R at a relatively high energy level. Also, as described above, the IR light emitting diode 55 of the IR transmitting section 50 of the IR repeater is, in general, physically placed in close proximity to the phototransistor I R 65 of the television receiver. The relatively high energy level of the IR light signal produced by the IR light emitting diode 55, and the close proximity of the IR light emitting diode 55 and the IR 65 phototransistor, more than resolves the slight bad tuning between the modulating frequency 47 kHz produced by the IR repeater and the frequency of the modulator signal expected by the television receiver 60. As described above, the transmitter section of the IR repeaters of the prior art produces an IR light signal which mimics the received by the receiving section. So, if the received light signal I R is corrupted with light I R of a compact fluorescent light, the transmitted light signal I R will be similarly corrupted. The performance of said IR repeaters is greatly diminished in the presence of compact fluorescent lights, and some become completely inoperable. However, an I R repeater, as illustrated in Figure 1, uses a receiver section that is resistant to interference from compact fluorescent light. The output signal of a receiver section (representing the demodulated encoded signal) is used to modulate a clean oscillator signal from an oscillator within the I R repeater. This newly generated and clean modulated signal controls the IR light emitter in the transmitting section. The light I R generated by the emitter I R in response to said signal does not include any interference from compact fluorescent light, and its operation is not degraded by the presence of compact fluorescent lights. Figure 3 is a schematic diagram illustrating in more detail the IR repeater illustrated in Figure 1. In Figure 3, an operating power source (not shown) produces a 5 volt power signal. A resistor R 1 is coupled between the source of the operating energy and a collector electrode of a transistor N PN Q 1. The signal electrodes of a detector I R 202 are coupled between a transmitter electrode of transistor Q 1 and a source of a reference potential (ground). The I R 202 detector also receives operating energy when coupled to the power source of operation. The I R 202 detector is tuned to a central modulating signal frequency of 45 kHz and is an I R detector model GP1 U78QG, manufactured by Sharp Electronics Corporation. A resistor R2 is coupled between the source of the operating energy and a base electrode of the transistor Q 1. A resistor R3 is coupled between the operating energy source and a collector electrode of a transistor N PN Q2. A transmitting electrode of transistor Q2 is coupled to ground. A resistor R4 is coupled between the source of the operating energy and a base electrode of the transistor Q2. A capacitor C 1 is coupled between the base electrode of transistor Q 2 and the collector electrode of transistor Q 1, and a capacitor C 2 is coupled between the base electrode of transistor Q 1 and the collector electrode of transistor Q 2. A resistor R6 is coupled between the power source of operation and a collector electrode of a transistor N PN Q3. A resistor R7 is coupled between a transmitting electrode of transistor Q3 and ground. A resistor R5 is coupled between the collector electrode of transistor Q2 and a base electrode of transistor Q3. The series connection of a resistor R8 and an IR light emitting diode 55 is coupled between the source of the operating energy and a collector electrode of a transistor N PN Q4. A transmitting electrode of transistor Q4 is coupled to ground The emitting electrode of transistor Q3 is coupled to a base electrode of transistor Q4. The light emitting diode IR 55 can be connected to the resistor R8 and the transistor Q4 via a long cable length, that is, with the intention of running from one room to another. The transistors Q 1, Q2, Q3, and Q4 are all N PN model M PS-A20 transistors, manufactured by Motorola Corporation. Table I contains preferred component values for the circuit illustrated in Figure 3. In operation, the IR detector 202 detects the presence of modulated IR light at the center frequency of the predetermined modulation signal (eg 45 kHz) while minimizes at the same time the parasitic IR light effect of compact fluorescent lights, as described above. When the modulated IR light is detected, the I R detector 202 is conditioned to conduct current between its two signal electrodes, and when no modulated IR light is detected, the IR detector 202 is conditioned to become non-conductive.
TABLE I When the IR detector 202 is non-conductive (indicating that both capacitors do not act as open circuits.) The base electrode of transistor Q2 is dragged high through resistor R4, and transistor Q2 is turned on, entraining the voltage at its collector electrode. at ground potential The base electrode of transistor Q3 is dragged down through resistor R5, turning off transistor Q3 The base electrode of transistor Q4 is dragged down through resistor R5, turning off transistor Q3. of the transistor Q4 is dragged down through the resistor R7, turning off the transistor Q4, and preventing the current from flowing through the light emitting diode IR 55. In summary, when the IR detector 202 does not detect modulated IR light, the diode IR emitter 55 does not emit IR light When the IR detector 202 is conductive (indicating that modulated IR light is being detected), the emitter electrode of transistor Q 1 is at coupled to earth. The combination of the transistors Q 1 and Q 2, the resistors R 1, R 2, R 3 and R 4, the capacitors C 1 and C 2 and the IR detector 202 operate in a manner known as a multivibrator oscillator (40 in Fig 1) adjusted to oscillate and generate a square wave at approximately 47 kHz. In this way, the signal on the collector electrode of transistor Q2 is a square wave signal of 47 kHz produced during periods when the IR light is detected by the IR detector 202. The IR detector 202 operates as a switch by turning the detector on and off. multivibrad or. The combination of the transistors Q3 and Q4, the resistors R5, R6, R7 and R8, and the light emitting diode IR 55 forms the transmission section (50), and operates in a manner known as a two-emitter follower amplifier. stages that responds to the output of the oscillator 40, to drive the IR light emitting diode 55 to be turned on and off at a frequency of 47 kHz during periods in which the m odulated IR light is detected by the IR detector 202. Thus, FIG. , the IR light emitting diode 55 generates an encoded IR light signal modulated at a frequency of 47 kHz. The IR detector 202 acts as the signal gate 30, controlling the transmission of the modulating signal of the oscillator 40 to the transmitting section 50. Figure 4 is a schematic diagram illustrating an alternative embodiment for an IR detector 202 illustrated in Figure 3. The IR detector 202 in the IR repeater illustrated in Figure 3, is a simple IR detector manufactured and tuned to have a central frequency modulating signal response of approximately 45 kHz. In Figure 4, the emitting electrode of transistor Q 1 is coupled to ground through the parallel connection of a first IR detector 204 and a second IR detector 206. The first IR detector 204 is tuned to a central modulating signal frequency. 38 kHz, and it is an IR detector model TFMS 1380 manufactured by TEMEC Telefunken Microelectronic GmbH. The second detector I R 206 is tuned to a central frequency modulating signal of 56 kHz, and is an I R detector model TFMS 1 560, also manufactured by TEMEC. An I R repeater as described above, provides reliable operation in the presence of compact fluorescent lights and operates with a variety of equipment manufacturers.