JPS5845860B2 - modulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a modulation circuit for a radio device having a frequency synthesis oscillator.

Conventionally, this type of device uses a single voltage-controlled oscillator for both transmission and reception, and applying direct modulation to the shared voltage-controlled oscillator not only modulates the transmitter carrier wave, but also modulates the receiving station. The output will be modulated.

When operating in the Frestalk system, there is no problem with the above system if a modulator is used during reception, but when operating in the simultaneous transmission and reception system, there is a drawback in that audio wraps around from transmission to reception.

It is also possible to have separate frequency synthesis oscillators for transmitting and receiving, and to apply modulation only for transmitting, but the circuit becomes complicated.

The present invention has been made to eliminate these drawbacks, and provides a modulation circuit that has good linearity and is economical.

FIG. 1 is a block diagram showing a conventional modulation circuit.

In Figure 1, 1 is a voltage controlled oscillator (hereinafter referred to as CO), 2 is a low-pass filter, 3 is a phase comparator, 4 is a variable frequency divider, 5 is a mixing circuit, 6 is a reference oscillator, 7 is a fixed frequency divider,
8 is a phase modulator, 9 is a modulation input terminal, and 10 is a CO output.

(2) The CO is a self-excited oscillator of LC, and the oscillation frequency can be controlled by adding a varactor diode to the LC tuning circuit and changing the control voltage.

The oscillation frequency of the VCO1 is mixed with the frequency of the reference oscillator 6, and the difference frequency is divided by the variable frequency divider 4 and applied to the phase comparator 3.

On the other hand, the frequency of the reference oscillator 6 is divided by a fixed frequency divider 7 and applied to one side of the phase comparator 3.

The phase comparator 3 detects the phase difference between the input from the variable frequency divider 4 and the input from the fixed frequency divider 7, and a voltage proportional to this phase difference passes through the low-pass filter 2 and is applied to the VCO1. Applied to the control signal input terminal.

VCOl - Low pass filter 2 - Phase comparator 3 - Variable frequency divider 4
- The mixing circuit 5 constitutes a negative feedback circuit, and if the frequency from the variable frequency divider 4 is higher than the frequency from the fixed frequency divider 7, it acts to lower the oscillation frequency of the VCOl, Work to raise the case.

On the other hand, the output of the fixed frequency divider 7 outputs the phase modulator 8 ( 3 The signal is applied to the phase comparator 3 through the signal.

When the output of the fixed frequency divider 7 undergoes phase modulation according to the audio signal, the phase of the VCO1 also changes according to the audio signal.

By changing the variable frequency division number of the variable frequency divider 4, the frequency M of the reference frequency of the reference oscillator 6 (M is the fixed frequency divider 7
The frequency of vcoi also changes in steps.

Next, one embodiment of the present invention will be described.

FIG. 2 is a block diagram showing an embodiment of the present invention, which includes a receiving VCO 11 and a transmitting VCO 12.

The receiving VCO 11 is controlled by a negative feedback loop of VCOll-low-pass filter 13-phase comparator 15-variable frequency divider 17-mixing circuit 18, but the output of the reference oscillator 20 is controlled by fixed dividers 21 and 22. When dividing the frequency and applying it to the phase comparator 15, no phase modulator is inserted.

On the other hand, the transmission VCO 12 is VCOl2 - low-pass filter 14
It is controlled by a negative feedback circuit composed of a one-phase comparator 16, a fixed frequency divider 23, and a mixing circuit 19.

A reference oscillator 20 frequency-divided by a fixed divider 21 and phase-modulated by a phase modulator 24 is applied to one side of the phase comparator 16 .

The phase modulator 24 is composed of a variable reactance phase modulator using a normal varactor, a cerasoid modulator, or the like, and is phase-modulated according to the audio signal.

The phase comparator 16 compares the phase of the difference between the transmitting CO oscillation frequency fT and the receiving CO oscillation frequency fR with the fixed frequency divider 23 and the output of the phase modulator 24. A negative feedback loop operates to reduce the phase difference to zero.

Therefore, the transmitting VCO 12 is phase modulated by the audio signal.

In this case, the cutoff frequency of the low-pass filter 14 must be higher than the upper limit of the audio frequency.

If the frequency shift of the transmitting VCO 12 is Δf, the output of the fixed frequency divider 23 will undergo a frequency shift of Δf/M3.

On the other hand, when the audio signal undergoes a frequency shift of Δm by the phase modulator 24, this Δm and Δf/M3 are controlled to be equal by the PLL loop, and the output of the VCO12 is modulated by M3 times Δm. I will receive it.

Therefore, the modulation capability of the phase modulator 24 is also multiplied by M3, making wide-angle modulation possible.

Note that 25 is a modulation input terminal, 26 is a transmitting VCO output terminal and is connected to the transmitter, and 27 is a receiving CO output terminal that is connected to the receiver.

Next, the difference between frequency fT and frequency fB is given by the following equation.

The output frequency of the fixed splitter 23 is (fT, fR,)/M3
and the output of the fixed frequency divider 21 is fo/M1
becomes.

Here, since both are controlled by the PLL loop so that they are equal, here fQ is the oscillation frequency M1 of the reference oscillator 20, M3 is the frequency division number of the fixed frequency divider 21, and M3 is the frequency division number of the fixed frequency divider 23. In the simultaneous transmission and reception method, which uses multiple line channels by switching,
Since the frequency interval Δf between the transmitter and the receiver is generally constant, both transmitting and receiving frequencies can be set simply by changing the variable frequency division number of the variable divider 17.

Therefore, compared to the case where frequency synthesis oscillators are provided separately for transmitting and receiving, the frequency setting operation becomes easier.

In the above explanation, the phase modulator is inserted between the fixed frequency divider and the phase comparator 16, but instead of this, the fixed frequency divider 23
A similar effect can be obtained by inserting it between the phase comparator 16 and the phase comparator 16.

As described above, according to the present invention, the transmission signal is transmitted to the transmission PL.
Since the transmitting PLL is synchronously controlled by frequency synthesis within the L loop, that is, the mixed output (difference signal) of the receiving ■CO and the transmitting ■CO, it is possible to prevent the transmitting modulation component from entering the received signal. Not only that, but also the generation of unnecessary harmonics included in the transmitted signal can be suppressed and eliminated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a modulation circuit using a conventional frequency synthesis oscillator, and FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 11 is a receiving voltage controlled oscillator, 12 is a voltage controlled oscillator, 13 and 14 are low-pass filters, 15° and 16 are phase comparators, 17 is a variable splitter, 18° and 19 are mixing circuits, and 20 is a A reference oscillator, 21 and 2223 are fixed frequency dividers, and 24 is a phase modulator.

Claims (1)

[Claims] A radio device having a frequency synthesis type frequency synthesis oscillator controlled by 11 reference oscillators, which has a receiving voltage controlled oscillator and a transmitting voltage controlled oscillator independently, and the control signal of the receiving voltage controlled oscillator is , a signal obtained by comparing the phases of a signal obtained by variable frequency division of the output of the receiving voltage controlled oscillator and a fixed frequency divided signal of the output of the reference oscillator, and a control signal of the transmitting voltage controlled oscillator. is a signal obtained by fixedly frequency-dividing the output of a mixing circuit, and a signal obtained by fixedly dividing the output of the reference oscillator and then applying phase modulation to the output of the transmitting voltage-controlled oscillator and the receiving voltage-controlled oscillator. A modulation circuit characterized in that the signal is obtained by comparing the phases of the signals.