JPH0783261B2 - Synthesizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Table of Contents] Outline Industrial field of application Conventional technology (Figs. 6 and 7) Problems to be solved by the invention Means for solving problems (Fig. 1) Action (FIG. 2) Embodiment (1) Configuration of one embodiment (FIGS. 3 and 4) (2) Operation of one embodiment (FIG. 5) Effect of the invention [Outline] The present invention uses a prescaler. In the synthesizer, a delay circuit is provided so that when the power of the prescaler is turned on / off, the change in the reactance component due to the change in the load of the VCO becomes almost zero.

[Industrial application field]

The present invention relates to a synthesizer, and more particularly to a synthesizer in which power of a prescaler is intermittently cut off and the output frequency of a VCO does not fluctuate substantially in order to reduce power consumption of the synthesizer.

[Conventional technology]

Synthesizers are used, for example, as oscillators in portable radios, automobile radios, etc., in which a very large number of transmission channels are provided in a narrow bandwidth band.

For example, when the communication channel is provided in units of 30 KHz in the band of about 825 MHz to 845 MHz, the synthesizer needs to instantaneously multiply the output frequency of the reference oscillator of 30 KHz by 27500 to 28166 times.

For this purpose, it is necessary to use a prescaler in addition to the programmable divider, divide the output frequency of the voltage controlled oscillator (VCO) in advance by the prescaler to some extent, and further divide it by the programmable divider.

A first example of such a conventional synthesizer will be described with reference to FIGS. 6 and 7. In this example, for convenience of explanation, an example in which a reference oscillator of 30 KHz is used and an output frequency of about 800 MHz is oscillated will be described.

In FIG. 6, 1 is a reference oscillator, which is composed of a VCO (voltage controlled oscillator), 2 is a phase detector, 3 is a loop
Filter, 4 VCO, 5 prescaler, 6 programmable divider, 7 phase detector, 8 reference voltage, 9
Is a loop filter, G _{1 to} G ₄ are gate circuits, SW is a switch, and OP is an operational amplifier.

When the switch SW is closed, the prescaler 5 is in operation, and the frequency of the reference oscillator 1 is multiplied by a multiple set by the prescaler 5 and the programmable divider 6 and output from the VCO 4. If the oscillation frequency of VCO4 changes, the output of VCO4
A gate circuit divided by a dividing ratio determined by the divider 6.
The output of G2, the phase difference in the output of the gate circuit G ₁ is the output of the reference oscillator 1 is caused, via the loop filter 3 the phase difference output from the phase detector 2 is formed of a low-pass filter VCO4 Is applied as a control signal, and the oscillation frequency changes so as to eliminate this phase difference. In this way, the VCO4 oscillates a signal of a constant frequency.

By the way, this prescaler 5 consumes a large amount of power, and it is required to save the power consumption when it is used as a portable radio device. Therefore, it is proposed that the switch SW of the prescaler 5 is closed during a call, but most of the switch SW is opened during standby and closed for a short time. By doing so, the power consumption of the prescaler 5 is significantly reduced.
When the switch SW is opened, the VCO4 oscillation frequency changes slowly, but sometimes the switch SW
Turn on to set the VCO4 oscillation frequency to the specified value.

When the switch SW is turned on, if the phase difference between the signals of the gates G ₁ and G ₂ is large, the output of the phase detector 2 also becomes large, and the VCO 4 momentarily causes a large frequency deviation. Therefore, the gates G ₃ and G ₄ and the phase detector 7
It is necessary to provide the amplifier 8, the loop filter 9 and the like.

That is, as shown in FIG. 7, the switch SW of the prescaler 5 is turned off during standby. Then, after the lapse of the period N, the switch SW is turned on and the gates G ₃ and G ₄ are turned on. By turning on this gate G ₃ , G ₄ , these gate G ₃ ,
If the output signal of G ₄ has a phase difference, the phase detector 7 outputs the phase difference signal, and if it is larger than the reference voltage 8 of the operational amplifier OP, the control signal is output. This output is applied to the reference oscillator VCXO via the loop filter 9 to control its frequency. Such control is repeated while the phase difference between G ₃ and G ₄ is large. Then gate G ₁ ,
G ₂ turns on, but at this time gates G ₃ and G ₄ or gate
Since G _1, the phase difference between the G ₂ of the output signal is little, so that the jump large frequency of the such as VCO4 not the output of the phase detector 2 is too large is prevented. Then, since the frequency becomes the specified value, the switch SW is turned off again. This is repeated during the standby state.

[Problems to be solved by the invention]

By the way, since the impedance of the prescaler 5 changes each time the switch SW of the prescaler 5 is turned on / off, VC
The load impedance of O4 changes. Since VCO4 has a very low Q (5th to 10th), it is easily affected by the change in this load impedance, and this prescaler (or buffer amplifier if a buffer amplifier is used).
When the power of (amplifier) is cut off, this load impedance fluctuates, and there is a problem that the VCO oscillation frequency changes.

Therefore, an object of the present invention is to provide a synthesizer in which the load impedance of the VCO does not change even when the power source such as the prescaler is cut off.

[Means for solving problems]

In order to achieve the above object, the synthesizer of the present invention,
As shown in FIG. 1, the output of the reference oscillating unit 20 is fed to the phase comparator 11
The output of the divider 15 is applied to this phase comparator 11, the output of the phase comparator 11 is applied to the VCO 13 via the low-pass filter 12, and the phase shifter is connected between the VCO 13 and the prescaler 14. The delay line 16 acting as is inserted. The reference oscillating unit 20 includes, for example, the reference oscillator 1, the phase detector 7, the operational amplifier OP, the loop
It may be composed of a filter 9, gates G ₃ , G _{4 and the} like.

[Action]

Switch for prescaler 14 when delay line 16 is not present
If SW is turned on, the impedance seen from VCO13 is the second
It is located at point A in Smith Chart in the figure. Then, when the switch SW is turned off, its impedance slightly fluctuates and it is positioned at the point B. In this way, the impedance changes from point A to point B depending on whether the switch SW is on or off.
The frequency changes due to the change to the point, but in the present invention, since the delay line 16 is used to move by θ in FIG. 2, when the switch SW is on, the impedance becomes the point A ′ and the switch SW. When is off, it is point B '. At this time, it is possible to draw an equal reactance line + jy passing through the points A'and B ', and the points A'and B'
The change in reactance at the point becomes zero. As a result, the frequency change of the VCO 13 can be zero.

The reason why the frequency change can be zero will be briefly described. When the resistance change is large, the frequency changes, but when the impedance change is very small, the frequency change depends on the reactance change.

Generally, there is a very large amount of attenuation between the VCO and the prescaler, and the impedance that changes when the load is applied from the VCO that controls (usually about 30 dB of attenuation) is extremely small (actually unmeasurable). . However, since the VCO has a very large tuning range, a slight change in impedance causes a large change in frequency. In such a case, the change in frequency due to the change in resistance can be almost ignored. Therefore, the frequency change can be made zero by inserting the delay line and setting the length of the delay line so that the reactance component does not change.

〔Example〕

(1) Configuration of One Embodiment One embodiment of the present invention will be described based on FIGS. 3 and 4 and with reference to other drawings.

FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. 4 is an example of its delay line which becomes a phase shifter.

In FIG. 3, the same parts as those in the other figures show the same parts, and 17, 18, and 19 are amplifires for buffers, respectively.

The programmable device 15 is of a pulse swallow type in which the frequency division ratio is changed by, for example, a serial bit, and the frequency division ratio of the prescaler 14 is also changed by the frequency division ratio of the programmable divider 15.

The delay line 16 acts as a phase shifter, and for example, as shown in FIG.
Short circuit with a wire W, or as shown in (b) of
It is possible to use a low-pass filter consisting of the inductance L ₁ and the capacitors C ₁ and C ₂ , or a high-pass filter consisting of the inductances L ₂ and L ₃ and the capacitor C ₃ as shown in (c). Of course, it is not limited to these.

The reference oscillating unit 20 is composed of the reference oscillator 1, the phase detector 7, the operation amplifier OP, the reference voltage 8, the loop filter 9, the gates G ₃ and G _{4 and the} like in FIG. 6, and the gates G ₁ and G ₂ The operation is also similar to that of FIG. 6 described above.

(2) Operation of one embodiment In the present invention, the presence of the delay line 16 causes the switch
When SW is turned on, the impedance seen from the VCO 13 is point A'in FIG. 2, and when it is turned off, it is point B '.
Since both A'point and B'point exist on the equal reactance line + jy, the reactance amount does not change, and therefore, the frequency variation of the VCO 13 due to the ON / OFF of the switch SW of the prescaler 14 is hardly present.

Actually, a variable capacitance diode such as a varactor diode is used as the resonator, and the capacitor of the lag lead filter discharges, so when the switch SW is off, VC
Since the control voltage of O13 slightly changes, there is a very slight frequency fluctuation as shown by the solid line in FIG.
However, when there is no delay line, there is a large frequency variation of Δf or more as shown by the dotted line in FIG.

〔The invention's effect〕

According to the present invention, even if the power source of the prescaler, which consumes the most power in the synthesizer, is intermittently cut off, the frequency change of the VCO can be suppressed to a value close to zero. Therefore, it is possible to provide a synthesizer with low power consumption and stable characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of the principle of the present invention, FIG. 3 is a block diagram of an embodiment of the present invention, FIG. 4 is an example of a delay line, and FIG. Explanatory drawing, FIG. 6 is an example of a conventional synthesizer, and FIG. 7 is a power switch SW of the prescaler in FIG.
FIG. 3 is an explanatory diagram of ON / OFF states of gates G ₁ , G ₂ , G ₃ and G ₄ . 1 ... Standard oscillator, 2 ... Phase detector 3 ... Loop filter, 4 ... VCO 5 ... Prescaler 6 ... Programmable divider 7 ... Phase detector, 8 ... Reference voltage 9 ... Loop Filter 11 …… Phase detector, 12 …… Loop filter 13 …… VCO, 14 …… Prescaler 15 …… Programmable divider 16 …… Delay line 17 ～ 19 …… Amplifier 20 …… Reference oscillator

Claims (1)

[Claims] 1. A synthesizer comprising a reference oscillator, a phase detector, a voltage control oscillator, a prescaler and a programmable divider, wherein the voltage control oscillator is provided between the voltage control oscillator and the prescaler. The synthesizer is characterized in that phase means (16) that does not change the reactance amount of the load impedance of is provided so that fluctuations in the oscillation frequency of the voltage controlled oscillator can be suppressed even when the power of the prescaler is cut off for a certain period.