JPS63263806A - Phase detection circuit - Google Patents

Abstract

PURPOSE:To perform phase measurement with high resolution, by multiplying an input signal to be detected by a reference signal having the same frequency component as that of the input signal, and multiplying the input signal multiplied by 2<n> to be detected by the reference signal multiplied by 2<n>. CONSTITUTION:A multiplier 10 multiplies the frequency of the input signal Vi to be detected by 2<n>, and an output signal is added on the input terminal on one side of a multiplier 11. A multiplier 12 multiplies the frequency of the reference signal CL outputted from a reference signal generator 4 by 2<n>, and the output signal is added on the input terminal on the other side of the multiplier 11. An A/D converter 14 which converts the output signal to a digital signal is connected to a low-pass filter 13 connected to the output terminal of the multiplier 11. A measured result obtained from the A/D converter 14 is provided with resolution higher than that of the measured result obtained from an A/D converter 7. The rough value of a phase difference is found from the measured result of the A/D converter 7, and the detailed value can be obtained from the measured result of the A/D converter 14.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a phase detection circuit used for detecting color signals of TV signals, etc., and more specifically, provides a circuit suitable for digital signal processing. It is something. .

[Prior Art] For example, the carrier color signal of a color video signal in the NTSC system is obtained by performing quadrature balance II on two color signals 1.0 with a D1 carrier wave on the transmitting side, and a reference subcarrier synchronized with the subcarrier. The summer signal and the Q signal can be reproduced by performing phase detection using the carrier signal. That is, if the magnitude of the ■ signal is El -, the magnitude of the Q signal is Eo=, and the angular frequency of the subcarrier is ωS, the carrier color signal @ec becomes e(−EI′CogωB t+Eo−sinωs t). This carrier color signal etH is added to the reference subcarrier signal [□
By multiplying by 5in (ωst 10) and inserting a low-pass filter on the output side to remove the second harmonic wave component, e c EQ Sin (ω Bt+ θ
)=(EoEl ′sinθ)/2+ (EoE
Q-008θ)/2.

Here, the phase of the reference subcarrier is set to θ−〇, and Ea′si
When adjusted to nωs1, a signal proportional to EQ' is obtained as an output, and when adjusted to θ-π/2 and adjusted to Ez''cosωst, a signal proportional to Et- is obtained as an output.

FIG. 4 is a circuit diagram showing an example of such a phase detection circuit. In FIG. 4, reference numeral 1 denotes an input terminal for the wave input signal v1 to be tested, which is connected to one input terminal of each of the multipliers 2.3. 4 is a reference signal generator that outputs a reference signal OL having the same frequency component as the test wave input signal v1, and its output signal @CL is connected to the other input terminal of the multiplier 2 and has a phase shift of +90 degrees. It is connected to the other input terminal of the multiplier 3 via a delay circuit 5 which provides . A low-pass filter 6 is connected to the output terminal of the multiplier 2, and an A/D converter 7 for converting the output signal into a digital signal is connected to the low-pass filter 6. A low-pass filter 8 is connected to the output terminal of the multiplier 3, and an A/D converter 9 for converting the output signal into a digital signal is connected to the low-pass filter 8.

With this configuration, the A/D converter 7
A digital signal corresponding to the in component is output, and a digital signal corresponding to the CO8 component signal 0 is output from the A/D converter 9.

[Problems to be solved by the invention] However, in order to obtain high-resolution measurement results with such a conventional configuration, it is necessary to use an A/D converter with high-resolution characteristics, and the circuit configuration The disadvantage is that it becomes complicated and the cost becomes high. Further, for this purpose, the time constant of the low-pass filter must be increased, which increases the settling time of the circuit.

The present invention has been made in view of these points, and an object of the present invention is to provide a phase detection circuit that has a relatively simple configuration and can perform high-resolution phase measurement.

[Means for Solving the Problems] The present invention, which achieves the above objects, includes: a reference signal generator that outputs a reference signal having a frequency component equal to that of the input signal to be tested; a first multiplier that multiplies the frequency of the reference signal; a second multiplier that multiplies the frequency of the reference signal by 2n; A multiplier that multiplies signals, and an A/D converter that converts the output signal of the multiplier into a digital signal.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention.
This figure shows an n-component system, and the same parts as in FIG. 4 are given the same i symbols. In FIG. 1, 10 indicates the frequency of the test wave input signal ■1 by 2n'i! j4F3, and its output signal is applied to one input terminal of the multiplier 11. 12 is a reference signal generator 4
This is a second multiplier that multiplies the frequency of the reference signal OL output from the multiplier 11 by 2n, and its output signal is applied to the other input terminal of the multiplier 11. Note that n is an integer. 1
3 is a low-pass filter connected to the output terminal of the multiplier 11, and an A/D converter 14 for converting the output signal into a digital signal is connected to this low-pass filter 13.

FIG. 2 is a waveform diagram for explaining the operation of the circuit configured as described above, in which (a) shows the reference signal CL, and (b)
) indicates the test wave input signal vi, and (C) indicates the reference signal OL.
shows the signal @CL' which is doubled, and (d) shows the signal Vi- which is obtained by multiplying the input signal V: to be tested.

Here, when the time difference between the reference signal OL and the wave input signal v1 is calculated, this time difference T is constant regardless of the multiplier of the reference signal OL and the wave input signal Vi. Therefore,
The phase difference when the reference signal @CL and the test wave input signal v1 are doubled is 2g3. That is, the reference signal CL
is sinωct, and the input signal Vi to be tested is sinωc.
If t+θ, the signal OL obtained by doubling the reference signal CL
= is sin 2ωat, and the test wave input signal Vi is 2
The multiplied signal vi' becomes sin 2ωci+2θ.

Thereby, the measurement results obtained from the A/D converter 14 have higher resolution than the measurement results from the A/D converter 7. In processing these measurement results, A/
An approximate value of the phase difference is obtained from the measurement results of the D converter 7, and the A/
D conversion! Detailed values are obtained from the measurement results of 114. Here, the multiplication number 2n is not limited to 2, and may be set to any value depending on the purpose.

According to such a configuration, a measurement result with high resolution can be obtained using an A/D converter with relatively low resolution. That is, if the resolution of the A/D converter 14 is m bits and the multiplication number is 2n, a measurement resolution of (m+n) pits can be obtained. Furthermore, since it is not necessary to increase the time constant of the low-pass filter, settling time can be shortened and high-speed measurement can be performed.

In the above embodiment, each multiplier 2, 11 is provided with a signal conversion system consisting of a low-pass filter and an A/D converter, but as shown in FIG. By switching the input signal of the multiplier 2 by .16, the number of signal conversion systems can be reduced to one.

In the above embodiment, an example has been described in which the detection circuit is used as a detection circuit for a color signal of a TV signal, but it is also effective for detection of various phase-modulated signals such as a modem signal.

Effect of E′R Light] As explained above, according to the present invention, relatively mttt
With this configuration, a phase detection circuit capable of high-resolution phase measurement can be realized, and the practical effect of E is great.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
3 is a circuit diagram showing another embodiment of the present invention, and FIG. 4 is a conventional circuit diagram. 1... Input terminal, 2.11... Multiplier, 4... Clock generator, 6.13... Low pass filter, 7.
14...-A/D converter, 10.12... Multiplier, 1
5゜Figure 3j Figure 4

Claims (1)

[Scope of Claims] A reference signal generator that outputs a reference signal having a frequency component equal to that of the input signal to be tested; a first multiplier that multiplies the frequency of the input signal to be tested by 2^n; and a frequency of the reference signal. a second multiplier that multiplies the input signal by 2^n, and a multiplier that multiplies the input signal to be detected by the reference signal and the input signal to be tested multiplied by 2^n by each multiplier, and the reference signal. A phase detection circuit comprising: an A/D converter that converts an output signal of a multiplier into a digital signal.