JPH0454005A - Pll type fm demodulation circuit - Google Patents

Abstract

PURPOSE:To reduce the operating time at the 2nd application of an FM modulation wave by intermitting the connection between a loop filter and a voltage controlled oscillator circuit in response to the interruption of the FM modulation wave with a detection signal from an amplitude detector and keeping a control voltage of the voltage controlled oscillator circuit at a prescribed value. CONSTITUTION:An electronic switch 4 intermite in response to a pulse from a pulse shaping circuit 3 to connect a loop filter 11 and a capacitor C alternately. That is, When an output from the shaping circuit 3 is present, the electronic switch 4 connects an output of the filter 11 to a voltage controlled oscillator circuit 12 to apply an intermittent FM modulation wave to the oscillation circuit 12 and connects the capacitor C to a loop of a PLL circuit 1. Thus, the control voltage of the voltage controlled oscillator circuit 12 is kept to a voltage just before the intermittent FM modulation wave is OFF. As a result, the operating time when a 2nd intermittent FM modulation wave is applied is reduced, resulting that the intermittent FM modulation wave is demodulated.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a PLL type FMul adjustment circuit.

<Prior art> PLL type F Mlj [J circuit ti In addition to the phase Jt comparison circuit for the F M modulation signal, the output of the phase comparison with the signal from the voltage controlled oscillation circuit is added to the loop filter, and is output as a baseband signal. FM output and voltage controlled oscillation circuit
It has an elliptical configuration that modulates and feeds back to the phase comparator circuit.

This t! The T''M modulated wave applied to the am circuit is generally a continuous modulated wave with respect to the time axis as shown in Figure 6 (a), but depending on the application, the T''M modulated wave as shown in (b) is used. An intermittent FM scattering wave input in the form of a pulsed signal may also be used.

<Problem to be solved by the invention> However, the above-mentioned PLL cannot handle such intermittent FM modulation waves.
When added to the mFMtM#4 circuit, there was a drawback that the demodulation circuit could not respond sufficiently, resulting in an output waveform as shown in the conventional example shown in FIG.

The present invention was made in order to solve the above-mentioned drawbacks of the prior art, and is a PLL type FM modulation system that can sufficiently cope with intermittent FM modulation waves! The purpose is to provide #1 equipment.

<Means for Solving the Problems> For this purpose, the present invention provides a PLL circuit that forms a PLL loop consisting of a phase comparison circuit, a loop filter, and a voltage controlled oscillation circuit, and demodulates a predetermined FM modulated wave; interposed between the loop filter and the voltage controlled oscillation circuit, an amplitude detector that inputs an intermittent FM modulated wave gated by a pulse signal of a predetermined period, performs amplitude detection of the wave, and outputs a detected signal; A basic feature of the present invention is that it includes a switching circuit that switches connection between the loop filter and the voltage controlled oscillation circuit on and off based on the detected signal.

Effect> The connection between the loop filter and the voltage controlled oscillation circuit is disconnected according to the intermittency of the FM modulated wave by the detection signal from the amplitude detector. When the connection is disconnected, only the capacitance of the loop filter is connected to the voltage controlled oscillation circuit, and the ia voltage controlled oscillation circuit control voltage is maintained at a predetermined value. Therefore, the operation time when the FM modulated wave is applied next time is shortened.

Example An embodiment of the present invention will be described below based on the drawings.

In FIG. 1, a PLL circuit 1 is composed of a phase comparator circuit 10, a loop filter 11 such as a rough filter, and a voltage controlled oscillation circuit 12, and there is no difference from the conventional one. The output of the loop filter 11 (illH) is output as a baseband signal via the high impedance buffer amplifier 5, and is also fed back to the voltage controlled oscillation circuit 12 via the electronic switch 4. Voltage controlled oscillation circuit 1
More precisely, as shown in FIG. 3, the electronic switch 4 is interposed between the resistor R and capacitance C of the loop filter 11, which is an integrating circuit. .

The intermittent FM modulated wave is input to the PLL circuit 1 and also to the amplitude detector 2. The amplitude detector 2 detects this intermittent FM modulated wave gated by a pulse signal of a predetermined period, and further performs pulse shaping! !
83 to output the pulse waveform shown in the upper row of FIG. 2. The on/off of the output of the pulse shaping circuit 3 directly corresponds to the on/off of the intermittent FM modulated wave (signal portion and non-signal portion).

The electronic switch 4 described above is configured to be turned on and off in response to pulses from the pulse shaping circuit 3, and to alternately connect the loop filter 11 and the capacitance C to the voltage controlled oscillation circuit 12.

That is, when the output from the pulse shaping circuit 3 is on, the electronic switch 4 outputs the loop filter 11 and connects it to the voltage controlled oscillation circuit 12 to transmit the intermittent FM modulated wave to the voltage controlled oscillation circuit 1.
2 and also connects the capacitance C to the loop of the PLL circuit 1. Since the intermittent FM modulated wave has no signal when the output from the pulse shaping circuit 3 is off, at this time, the capacitance C1 is disconnected from the PLL circuit circuit and connected only to the voltage controlled oscillation circuit 12, and the capacitance C1 is disconnected from the PLL circuit circuit. It is configured to supply the charges accumulated in the voltage controlled oscillation port wT12.

Upper Ke! Although various configurations can be adopted as the child switch 4, in this embodiment, a diode bridge is used as shown in FIG. 4.

In the above configuration, one intermittent FM modulated wave is input to the PLL circuit 1 and also input to the amplitude detector 2, and the pulse shown in the upper part of FIG. 2 is supplied to the electronic switch 4 via the pulse shaping circuit 3. Between t and t2, the electronic switch 4 is turned on, and a loop of the LL circuit 1 is formed, and the high impedance buffer amplifier 5 outputs the waveform shown in the middle part of FIG. That is, the FM modulated wave is faithfully FM demodulated between t1 and t2. Then, between t2 and t1, the electronic switch 4 is turned off, the loop of the PLL circuit 1 is cut off, and only the capacitance C is connected to the voltage controlled oscillation circuit 12. Connecting. At this time, the capacitance C is t.

Since there is a potential corresponding to the potential at time, the voltage at time t2 is maintained as the control voltage of the voltage controlled oscillation circuit 12 between t2 and t3 unless there is any other charge leakage. Next, between t and t4, the electronic switch 4 is turned on and a loop of the PLL circuit 1 is formed, and the potential of the output waveform changes from point B to 0.
point and continue FM demodulation. Thereafter, similar operations are repeated, and FM demodulation is performed only when the electronic switch 4 is on.

Also, when the electronic switch 4 is off, a predetermined potential is maintained, and when the electronic switch 4 is turned on, the operating time is shortened, so intermittent FM
It becomes possible to demodulate the modulated wave.

Note that, if necessary, an appropriate gate means may be used to extract only the output when the electronic switch 4 is on.

FIG. 5 shows another embodiment. In this example, input F
When the M modulated wave is a continuous modulated wave as shown in FIG. 6(a), the electronic switcher 8 is turned on and off by the switch pulse generator 7 to convert it into an intermittent FM modulated wave. ing.

In this configuration, the electronic switch 4 uses the output of the switch pulse generator 7 whose waveform is shaped by the pulse shaping circuit 3. The other configurations are the same as those shown in FIG.

As explained above, according to the above configuration, when the intermittent FM modulated wave is not applied to the voltage controlled oscillation circuit 12, the capacitance C of the loop filter 11 is supplied only to the voltage controlled oscillation circuit 12.

The control voltage of the voltage controlled oscillation circuit 12 can be maintained at a voltage just before the intermittent FM modulated wave is turned off.

The operation time when intermittent FM modulated waves are added to the result can be shortened. As a result, intermittent demodulation of FM modulated waves becomes possible.

<Effects of the Invention> As explained above, the PLL type FM ttht of the present invention
The modulation circuit forms a PLL loop consisting of a single phase comparison circuit, a loop filter, and a voltage controlled oscillation circuit, and includes a PLL circuit that demodulates a predetermined FM modulation wave, and an intermittent FM modulation gated by a pulse signal of a predetermined period. an amplitude detector that inputs a wave, performs amplitude detection on the detected signal, and outputs a detected signal; and an amplitude detector that is interposed between the loop filter and the voltage controlled oscillation circuit, and that operates based on the detected signal between the loop filter and the voltage controlled oscillation circuit. Since it has a switching circuit that switches the connection between the two and on and off, it has the effect of making it possible to demodulate the FM modulated wave intermittently.

[Brief explanation of drawings]

1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of its operation, FIG. 3 is a circuit diagram of the loop filter 11, FIG. 4 is a circuit diagram showing an example of the electronic switch 4, and FIG. FIG. 5 is a block diagram showing another embodiment, and FIG. 6 is an explanatory diagram of FM modulated waves. 1: PLL circuit, 2: Amplitude detector, 3: Pulse shaping circuit, 4: Electronic switch, 5: High impedance buffer amplifier 1.7: Switch pulse generator, 8: Electronic switcher, 1o: Phase comparison circuit, 11: loop filter,
12:@Pressure control oscillation circuit. Patent applicant: Clarion Co., Ltd. Representative: Patent attorney Kiyoshi Takahashi

Claims (1)

[Claims] A PLL circuit that forms a PLL loop consisting of a phase comparator circuit, a loop filter, and a voltage controlled oscillation circuit and demodulates a predetermined FM modulated wave; FM
an amplitude detector that inputs a modulated wave, performs amplitude detection on the modulated wave, and outputs a detected signal; and an amplitude detector that is interposed between the loop filter and the voltage controlled oscillation circuit, and that performs voltage control with the loop filter based on the detected signal. A PLL type FM demodulation circuit comprising: a switching circuit that switches connection with an oscillation circuit on and off; and a PLL type FM demodulation circuit.