JPS598424A - Frequency adjusting device - Google Patents

Abstract

PURPOSE:To adjust easily an input signal to a prescribed frequency with high accuracy, by using also a microcomputer without using a frequency counter. CONSTITUTION:A beat waveform B is obtained by inputting an input signal A to an amplifier circuit 2 with a limit of gain and mixing the signal at a reference signal generating circuit 1. A signal waveform C is obtained by passing this waveform B through a reference frequency eliminating circuit 5. The input signal A is changed into a signal D having f0 of frequency and a maximum output level by passing the signal waveform C through an LPF6, where f0 is the frequency to be adjusted for the input signal A and the frequency of the circuit 1. The signal D is converted into a digital signal at an AD converter 7 and given to a CPU9 through an input/output circuit 8. The input signal passes through a phase detecting circuit 4 to recognize whether the frequency of the input signal A is larger or smaller than the f0 and it is discriminated whether the output is H or L level and the result is given to the circuit 8. Thus, the frequency adjustment with high accuracy is attained with the comparison of the basic frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency adjustment device suitable for adjusting the frequency of a voltage controlled oscillator used, for example, in a stereo demodulation circuit of a receiver, and in particular, the present invention relates to a frequency adjustment device suitable for adjusting the frequency of a voltage controlled oscillator used in a stereo demodulation circuit of a receiver. By mixing it with a reference signal, it is possible to adjust to the reference frequency quickly and accurately.

Conventionally, when adjusting the frequency of a voltage controlled oscillator in a demodulation circuit of a stereo receiver or the like, the signal from a measurement point is adjusted to a reference frequency while reading the value of a frequency counter.

However, with this method, there is a problem in that the adjustment process takes time to achieve accurate adjustment, and the expectation of high-speed adjustment is tedious. Even at low frequencies, in order to solve this problem, a highly accurate and expensive frequency counter with a short gate time and a large number of digits is required.

The present invention solves such problems by providing a high-precision frequency adjustment device that can easily adjust an input signal to a predetermined frequency by using a microcomputer without using a frequency counter. This is what we provide.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3.

In Figure 1, 1 is a high-precision reference signal generation circuit that generates a signal with the same frequency as the frequency of the input signal to be adjusted as a reference signal, and 2 is a gain limiter to keep the level of the input signal constant. It is an amplifier circuit. A mixing circuit 3 mixes the output signals of the reference frequency generating circuit 1 and the gain limiting amplifier circuit 2.
The reference frequency removing circuit 5 removes only the reference signal. 6 is a low-pass filter whose output level changes depending on the frequency, and 7 is a central processing unit (hereinafter simply referred to as CPU) that allows input of the signal of the difference in frequency between the input signal and the reference signal to 9. 4 is an AD (analog-digital) converter that converts the output signal of the low-pass filter 6 into a digital signal, and 4 is an input signal A, that is, the output signal of the gain limiting amplifier circuit 2, and a reference signal generator 1.
8 is an input/output circuit to which the output of the AD converter 7 and the output of the phase detection circuit 4 are input; 10 is an input/output circuit connected to the CPU 9; This is a pass line that connects the output circuit 8.

In the second configuration, the signal of the voltage controlled oscillator in the stereo receiver to be adjusted as shown in FIG. By mixing with circuit 1, a beat waveform B as shown in FIG. 2(B) is obtained. From this beat waveform B, a signal waveform C shown in FIG. 2(C) is obtained by passing it through the reference frequency removal circuit 6. Here, if the frequency to be adjusted by the input signal person and the frequency of the reference signal generation circuit 1 are fo, then by passing the signal waveform C through the low-pass filter 6, the input signal A will be fo by the characteristics shown in FIG. The signal changes to the one with the maximum output level. This signal is converted into a digital signal by the AD converter in the next stage, and sent to the CPU 9 through the input/output circuit 8. Also, the frequency of the input signal is the reference frequency f.

In order to know whether it is larger or smaller, the phase detection circuit 4
, judge whether the output is H level or B level,
Send it to the input/output circuit 8.

As described above, the present invention enables high-speed and highly accurate frequency adjustment by comparing with a reference frequency, and when implemented for frequency adjustment of a demodulation circuit of a stereo receiver, etc., the adjustment work can be performed easily. It can be easily automated and the adjustment time can be greatly shortened, which is an excellent effect75'! !
'r will be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of main parts showing one embodiment of the present invention, and FIG.
Figures (A), (B), and (C) show signal waveforms at various parts in Figure 1, and Figure 3 shows an example of the frequency characteristics of the low-pass filter used in the present invention. 1...ノ, (Iv Shinkyu generation circuit, 2...R) limiting amplification circuit, 3...Mixing circuit, 4...Seki Iken 11 soup 11 path, 6... ), (71, 11 round θl number removal circuit, 6...low-pass filter, 7...A
DI inverter, 8...input/output circuit, 9...,
・CPUL. Name of representative (Benyo) 1. Figure 1: 1st year junior high school student, Toshio and 1 other person

Claims (1)

[Claims] a reference frequency removal circuit that removes a reference frequency from the output signal of the signal circuit having the same frequency as the frequency to be adjusted of the input signal; a phase detection circuit that detects the phase of the reference signal and the input signal; The present invention includes a low-pass filter that detects the maximum point of the signal from the output signal, and a signal processing circuit that detects the adjustment point of the human input signal using the output of the low-pass filter and the output of the phase detection circuit. Characteristic frequency adjustment device.