KR830000899B1 - Frequency tracking circuit - Google Patents

Abstract

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Description

Frequency tracking circuit

1 is a schematic diagram of a conventional circuit.

2 to 4 are diagrams for explaining the operation thereof.

5 is a schematic diagram of an example of the circuit of the present invention.

6 to 8 are diagrams for explaining the operation thereof.

9 is a schematic diagram of an example of a non-ingtex type color television receiver using the circuit of the present invention.

The present invention relates to a frequency tracking circuit capable of treating a signal having a variable frequency such as an FM modulated signal, a PM modulated signal, an AM modulated signal having an unstable carrier frequency, and the like as a state in which interference signal elimination characteristics and S / N are improved.

As the FM demodulation circuit of the FM receiver, the circuit shown in FIG. 1 has been proposed.

This means that the FM modulated signal to be demodulated from the input 11 is supplied to the phase comparator 14, on the one hand, via the tracking filter 12, through the limiter 13, and on the other hand, a 90 ° ideal phaser. The comparator 16 is supplied to the phase comparator 14 through the limiter 16, and the output voltage of the phase comparator 14 is supplied through the loop filter 17 to the tracking filter 12 through the loop amplifier 18. The output stage 19 is derived from the loop amplifier 18 by being supplied as a control voltage of the center frequency, and the tracking filter 12 has an input stage 21 as a resistor, for example, as shown in FIG. It is connected to one end of the coil 23 via 22, and the series circuit of the variable capacitance diodes 24 and 25 is connected in parallel with the coil 23, the intermediate point of the coil 23 is grounded, In response, the condenser 26 is connected in parallel with the coil 23 and the control voltage is applied to the connection point 27 of the variable capacitance diodes 24 and 25. Adjuster, may be from both ends of the coil so that the output signal can pull out.

The amplitude characteristic of the tracking filter 12 is as shown by the curve 31 in FIG. 3, and the phase characteristic when the center frequency fc is fixed is as shown by the curve 32 in this figure. In addition, the phase of the input signal is φ ₀ , the output signal of the tracking filter 12, that is, the phase of one input signal of the phase comparator 14 is φ ₁ , the output signal of the phase shifter 15, that is, the other side of the phase comparator 14. If the phase of the input signal of φ ₂ is φ ₁ -φ ₂ = (φ ₁ -φ ₀ )-(φ ₂ -φ ₀ ) = (φ ₁ -φ ₀ ) -90 °, the phase difference φ _1- The characteristic of phi ₂ becomes like the curve 33 of FIG. Thus, the characteristics of the output voltage with respect to the input / output characteristic phase difference φ ₁ -φ ₂ of the phase comparator 14 are as shown in the solid line of FIG. 4, and the loop amplifier 18 is an inverting amplifier, and therefore the phase difference φ _1- . The characteristic of the output voltage of the amplifier 18 with respect to phi ₂ becomes like the broken line of FIG.

When the input FM modulated signal is unmodulated, i.e., at a carrier frequency, the variable capacitance diode 24 of the filter 12 can be centered at the carrier frequency described above. And a bias is applied to the control voltage given to (25). First, when the FM modulated signal of the input is unmodulated, that is, at the carrier frequency, the phase difference φ ₁ -φ ₀ is 0 ° and the phase difference φ ₂ -φ ₀ is + 90 °, so the phase difference φ ₁ -φ ₂ is −. 90 °, therefore, at this time, the output voltage of the phase comparator 14 and the output voltage of the loop amplifier 18 become zero.

If the FM modulation signal of the input is modulated and its instantaneous frequency is higher than the carrier frequency, the phase difference φ ₁ -φ ₀ becomes-and the phase difference φ ₂ -φ ₀ is + 90 °, so the phase difference φ ₁ -φ ₂ is less than -90 degrees (to the-side), therefore, the output voltage of the phase comparator 14 becomes-, the output voltage of the loop amplifier 18 becomes +, and the variable capacitance diode of the tracking filter 12 The voltages given to (24) and (25) become larger than the bias voltage, so that the center frequency fc of the filter 12 moves upward. At this time, when the moving amount of the center frequency fc is too large, and the moved center frequency fc is higher than the instantaneous frequency, the phase difference φ ₁ -φ ₀ becomes + and the phase difference φ ₂ -φ ₀ is + 90 °, so that the phase difference φ ₁ -φ ₂ becomes larger than -90 ° (becomes the + side), therefore, the output voltage of the phase comparator 14 becomes +, the output voltage of the loop amplifier 18 becomes-, and the tracking filter 12 The voltages given to the variable capacitance diodes 24 and 25 are less than the bias voltage, so that the center frequency fc of the filter 12 moves to the lower side. Therefore, eventually, the center frequency fc settles when it becomes equal to the instantaneous frequency.

Conversely, when the instantaneous frequency is lower than the carrier frequency, the reverse operation is performed as described above, and the center frequency fc is stabilized at the same place as the instantaneous frequency.

In this manner, according to this circuit, the center frequency fc of the tracking filter 12 follows the instantaneous frequency of the input FM modulated signal.

Thus, since the control voltages of the variable capacitance diodes 24 and 25 of the filter 12 and the center frequency fc of the filter 12 are compared, the control voltages of the variable capacitance diodes 24 and 25, i.e., the output stages, are compared. The voltage obtained in (19) is the demodulation output of the input FM modulation signal.

However, in this circuit, a differential circuit is used as the ideal phase 15 of 90 degrees. As a result, any high-frequency disturbance signals, noise, etc. in the input signals are amplified as these outliers 15 and cause disturbance of the loop. An integrating circuit is used as the ideal phase 15 of 90 ° (expressed as -J), so that the operation of the above-described shape is performed even if the loop amplifier 18 is implemented in the same phase amplifier. However, in this case, if there is a low inverse disturbance signal and noise in the input signal, this is augmented as the outlier 15, which also causes disturbance of the loop.

In view of this, the present invention is intended to prevent disturbance of the rupee caused by the high frequency and low frequency disturbance signals and noise.

5 shows an example of the frequency tracking circuit of the present invention, in which a signal from the input terminal 41 is supplied to the tracking filter 43 through the adder 42, and the output signal of the filter 43 is supplied to the attenuator 44. Supplied to the attenuator, the attenuated signal is supplied to the adder 42 and added to the signal from the input terminal 41, i.e., the output of the tracking filter 43 is attenuated and fed back to the input, and thus the tracking filter The output signal of 43 is supplied to the phase comparator 47 through the ideal phase 45 of 90 degrees, and through the limiter 46, and the output signal of the adder 42, that is, the input of the tracking filter 43, is input. The signal is supplied to the phase comparator 47 through the limiter 48 so that the output voltage of the phase comparator 47 is centered on the tracking filter 43 through the loop amplifier 50 and through the loop amplifier 50. It is supplied as a control voltage of the frequency. Furthermore, in the case of the FM demodulation circuit, the output stage 51 is exposed from the loop amplifier 50.

The tracking filter 43 is configured as shown in, for example, FIG. 2, so that the amplitude characteristics of the filter 43 itself and the phase characteristics when the center frequency fc is fixed are different from the curves 31 and 32 of FIG. Become together. Therefore, if the attenuation rate in the attenuator is A (output is A when input is 1, but 0 <A <1), that is, the amplitude characteristic and the phase characteristic of the output signal of the adder 42, that is, the output signal of the tracking filter 43 Is shown as curves 34 and 35 in FIG. 6, so that the amplitude characteristics and satellite characteristics of the output signal of the tracking filter 43 are as shown in curves 36 and 37 in FIG. The phase of the input signal φ ₀ , the output signal of the adder 42, that is, the phase of one input signal of the phase comparator 47, the phase of the output signal of the φ ₂ tracking filter 43, and the φ _{3 or more} phaser 45. Φ ₁ -φ ₀ = (φ ₃ -φ ₀ ) + (φ ₁ -φ ₃ ) = (φ ₃ -φ ₀ ) according to the phase of the output signal of the phase comparator 47, that is, the input signal of the other side of the phase comparator 47 Since it becomes + 90 °, the characteristics of the phase difference φ ₁ -φ ₂ become like the curve 38 in FIG. 8, and are φ ₁ -φ ₂ = (φ ₁ -φ ₀ )-(φ ₂ -φ ₀ ). , The characteristics of the phase paper φ ₁ -φ _{2 become like} the curve 39 of FIG. 8. In addition, the input / output characteristics of the phase comparator 47, that is, the characteristics of the output voltage with respect to the phase difference φ ₁ -φ ₂ become like the solid line of FIG. 4, so that the two amplifiers 50 become the same phase amplifiers, and therefore the phase difference φ ₁ -φ characteristic of an output voltage of the amplifier (50) treating _{the second} is also, as a fourth-degree solid.

According to this circuit, by the operation corresponding to the circuit operation of FIG. 1, the center frequency fc of the tracking filter 43 follows the instantaneous frequency of the input signal, and the output stage 51 obtains the FM demodulation output of the input signal. .

As the abnormal phase 45 of 90 degrees, a differential circuit is used in this case. However, the operation of the same form is carried out even if the ideal phase 45 is provided with an ideal phase (represented by -j) of 90 degrees from the integrating circuit on the input side of the limiter 48.

Therefore, according to this circuit, even if there are high to low frequency disturbance signals and noise in the input signal, the two signals supplied to the phase comparator 47 are all through the band pass filter configured as the tracking filter 43 together. Since disturbance signals and noises of high and low frequencies are eliminated, disturbance of the loop due to the disturbance signals and noise does not occur.

In addition, since the output can be derived from the limiter 46 or 48, in this case, the input signal can be pulled out in a state in which the disturbance signal removing characteristic and the S / N are improved.

In the frequency tracking circuit of the present invention, the beam index type color television receiver has a single electron beam as an image tube, and red, green, and blue phosphor stripes have a fluorescent surface in which the horizontal direction is arranged, and the index on the inner surface of the fluorescent surface. Phosphor stripes are arranged in a horizontal direction, and color conversion is also performed based on the index signal obtained by scanning the electron beam by the index phosphor stripes, and when the electron beam scans the red phosphor stripes, the red primary color signal is used. As a result, density modulation is performed as a primary color signal when scanning green phosphor stripes, and as a primary color signal when scanning blue phosphor stripes.

In this case, conventionally, the output signal of the photodetector is supplied to a band pass filter having a fixed center frequency, and an index signal having a frequency determined as the pitch of the index phosphor stripes and the scanning speed of the electron beam is extracted, and this index signal is a PLL. The frequency is multiplied by the circuit, and the output signal of this PLL circuit is divided by a ring counter to obtain three phase gate arms out of phase by 120 ° so that the primary color signals are gated. Each primary color signal is sequentially gated so that the converted primary color signal is given to the receiving tube.

However, in general, since the linearity in the horizontal direction deteriorates and the scanning speed of the electron beam changes, the frequency of the index signal fluctuates. For this reason, as the band pass filter for capturing the above-described index signal, a relatively wide band having a low Q is used.

However, the output signal of the photodetector is intermodulated by the luminance signal, the color signal, the gate arms described above, and has a high and low disturbance signal other than the index signal, and includes noise generated by the photodetector. Doing. For this reason, as described above, when the bandwidth of the filter is wide, the disturbance signal removal characteristic and the S / N become worse, and the image quality deteriorates.

However, if the frequency tracking circuit of the present invention is used in place of the band pass filter described above, the bandwidth of the band pass filter configured as the tracking filter 43 can be narrowed, and the frequency of the index signal of the input can be followed. Since the center frequency fc of the band pass filter fluctuates, the index signal can be represented as a state in which the disturbance signal removing characteristic and the S / N are improved, and the image quality is improved. In this case, the ideal phase of 90 ° can also serve as the above-described PLL circuit.

9 is an example of a beam index type color television receiver using the frequency tracking circuit of the present invention, and 60 is a beam index type color receiver, and a photodetector 70 is provided on the outer axis of the panel portion. The output signal of the detector 70 is supplied to the above-described frequency tracking circuit, and the index signal is taken out from the tracking filter 43, which is supplied to the PLL circuit 80 through the limiter 46.

에 분극되어, 그 분주팔즈가 위상비교기(81)에 공급되어, 위상비교기(81)의 출력전압이 로우패스필타(84)를 통해서 발진기(82)에 공급되어, 발진기(82)로부터, 인덱스신호의 N배인 주파수, 즉 색형광체 스트라이브의 1조의 핏치와 전자빔의 주사속도로서 정하는 여러 가지 트리프레트주파수의 3배의 주파수의 팔즈가 얻어진다.In the PLL circuit 80, the index signal is supplied to the phase comparator 81 through the limiter 46, and the output arms of the voltage controlled oscillator 82 are supplied to the divider 83.

Polarization is applied to the phase comparator 81, the output voltage of the phase comparator 81 is supplied to the oscillator 82 through the low pass filter 84, and the index signal from the oscillator 82 is supplied. A frequency of N times, i.e., a pair of pitches of the color phosphor stripes and a frequency of three times the frequency of the various triplet frequencies determined as the scanning speed of the electron beam are obtained.

Here, the output arms of the divider 83 of the PLL circuit 80 have the same frequency as the index signal through the limiter 46 and the phases are slipped by 90 °. Is supplied to the phase comparator 47 described above.

Therefore, the phase shifter 45 of 90 degrees is not necessary on the input side of the limiter 46. Thus, the output arms of the frequency divider 83 of the PLL circuit 80 are supplied to the gate arms at the time of occurrence of the ring arms 90, and are regulated by the mode set arms PMS to gate the red, green, and blue primary colors signals. The three-phase gate arms to be obtained are supplied to the gate circuits 100R, 100G and 100B so that the red, green and blue primary color signals E _R , E _G and E _B are sequentially gated and converted therefrom. The primary color signal is supplied to, for example, the first grit 61 of the water pipe 60 through the video amplifier.

Claims (1)

An input signal of varying frequency is supplied to the tracking filter, the output of the tracking filter is attenuated and fed back to the input, and the input signal and the output signal of the tracking filter are compared in phase, and the comparison output voltage is supplied through the loop filter. And a frequency tracking circuit supplied to the tracking filter at a control voltage of the center frequency so that the center frequency of the tracking filter follows the frequency of the input signal.

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