JPS6098707A - Fm detection circuit - Google Patents

Abstract

PURPOSE:To decrease distortion and to improve the threshold value by detecting an oscillation signal generated by a voltage controlled oscillator of a PLL circuit. CONSTITUTION:The titled FM detection circuit does not use a demodulation signal at a terminal 4b including distortion due to the nonlinearity of the voltage controlled oscillator 7 of the PLL circuit 4 but uses an oscillation signal of the voltage controlled oscillator 7. Since the oscillation signal is synchronized with an FM signal and phase noise is decreased, the distortion of the demodulation signal detected by a pulse count detector 16 is decrease and the threshold value is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM detection circuit, and more particularly to an FM detection circuit that reduces distortion and improves the threshold of the received signal level at which the signal-to-noise ratio rapidly deteriorates.

Generally, in FM detection circuits, reduction of distortion and improvement of threshold are design goals for evaluating the performance of FM detection circuits. To improve the threshold, use the PL shown in Figure 1.
There is an L detection circuit and an FM negative @ sending circuit. The PLL detection circuit shown in FIG. 1 detects an FM signal manually input from terminal 4& of a PLL circuit 4 via an antenna 1, an RF unit 2, and an intermediate frequency amplifier 3. The detected demodulated signal is sent from the output side of the low-pass filter via the terminal 4b to the audio circuit 8 and to the speaker 9. The threshold of the PLL detection circuit is improved by feedback from the low pass filter 6 to the voltage controlled oscillator 7 and the phase comparator 5. FM that simultaneously reduces phase distortion and improves threshold
A circuit shown in FIG. 2 has been proposed as a detection circuit. The pass band of the circuit shown in FIG. 2 is formed to obtain a sum frequency and a difference frequency such that the frequencies at the input side of the front mixer 10 and the output side of the rear mixer 12 of the band pass filter 11 are equal. Therefore, if the input signal changes, the passband of the bandpass filter 11 will change, but if the same amount of change is applied to the voltage controlled oscillator 13 via the terminal 13a, the passband of the bandpass filter 11 will not change. . In addition, since the pulse count detector 16 shown in FIG. 3 does not pass through any nonlinear circuit, FM detection can be performed with low distortion. In FIG. 3, reference numeral 17 is a limiter, 18 is a differentiating circuit, 19 is a monostable multi-pie break, and 20 is an integrating circuit.

In the conventional circuit example described above, a circuit that simultaneously improves distortion, threshold, and lead is the circuit shown in Figure 2 and the FM negative feedback circuit (
This is a composite of the dotted line portion in Figure 2). but,
This circuit has the disadvantage of requiring the use of two mixers.

The present invention has been made in consideration of the above points, and an object of the present invention is to provide an FM detector that improves υ distortion and threshold by detecting an oscillation signal generated by a voltage controlled oscillator of a PLL circuit. .

An embodiment of the FM detection circuit according to the present invention will be described below with reference to the drawings.

Components that are the same in FIG. 3 and FIG. 1 are designated by the same reference numerals, so their explanation will be omitted.

In FIG. 3, 4 is a PLL circuit. PLL circuit 4
is inputted via the intermediate frequency amplifier 3 to the terminal daKFM encoded signal. The FM signal input to the terminal 4a is sent to the phase comparator 5.
The oscillation signal of the voltage controlled oscillator 7 is output by the PLL Luzo which passes through the low/4' filter and the voltage controlled oscillator 7. The circuit that outputs the demodulated signal from the loaf filter to the audio circuit 8 via the terminal 4b is disconnected, and the output side of the voltage controlled oscillator is connected to the input side of the pulse count detector 16 via the terminal 4C. The demodulated signal output from the pulse count detector 16 is sent to the speaker 9 via the audio circuit 8.

In the FM detection circuit in the above embodiment, the voltage controlled oscillator 7
The oscillation signal of the voltage controlled oscillator 7 is used instead of the demodulated signal of the terminal 4b which includes distortion due to non-linearity. Since the oscillation signal is synchronized with the FM signal and the phase noise is reduced, the distortion of the demodulated signal detected by the pulse count detector 16 is reduced and the threshold is improved.

Since the FM detector according to the present invention has a configuration including a PLL circuit and a detection means for detecting an oscillation signal output from a voltage controlled oscillator of the PLL circuit, the FM signal to be detected is a synchronized oscillation signal. It has special features. This has the effect of reducing distortion related to nonlinearity caused by the voltage controlled oscillator, and at the same time improves the threshold. In addition, various conveniences such as being able to form circuits using IC circuits can be expected.

[Brief explanation of drawings]

FIG. 1M2 is a block diagram of a conventional FM detection circuit, and FIG. 3 is a block diagram showing an embodiment of the FM detection circuit according to the present invention. In the figure, 1 is an antenna, 2 is an RF unit, 3 is an intermediate frequency amplifier, 4tiPLL circuit, 5 is a phase comparator, 6 is a low-pass filter, 7.13 is a voltage controlled oscillator, 8 is an audio circuit, 9 is a speaker, 10 .12 is a mixer, 11
15 is a low-pass filter, 16 is a pulse count detector, 17 is a limiter, 18 is a differentiation circuit, 19 is a monostable multivibrator, and 20 is an integration circuit. Patent applicant Yaesu Musen Co., Ltd. No. 11!1 M2F! ! J 13a whistle 3gg

Claims (1)

[Claims] 1. A phase comparator that compares the phase of the FM signal and the oscillation signal output from the voltage controlled oscillator, and a low-pass filter that receives the output signal of the phase comparator and outputs an error signal;
An FM detection circuit comprising: the voltage controlled oscillator to which an error signal is input; and detection means for detecting the oscillation signal.