KR200235005Y1 - Loop Filter of FM Detection Circuit - Google Patents

Abstract

The present invention can supply a high quality output screen by driving the transistor according to the supply voltage of the power stage by adjusting the variable resistor, controlling the noise component of the filter unit, and increasing the threshold level by increasing the bandwidth of the capture range. A loop filter of an FM detection circuit, comprising: a first resistor connected between an output terminal of a phase comparator and an input terminal of an oscillator, a second resistor and a first capacitor connected in parallel with each other in parallel with the first resistor; A second capacitor for coupling connected between the comparator and the second resistor to block direct current components, a third capacitor and a third resistor sequentially connected between the oscillator and the first capacitor to suppress a noise signal; By adjusting the noise component of the filter unit, the power supply voltage of the power supply terminal may be changed to change the capture range. In the loop filter of the FM detection circuit comprising a voltage regulator for applying, wherein the voltage regulator, the emitter is grounded, the collector is connected to the third resistor, the base is connected to the second capacitor and the fourth resistor The transistor is connected in series to stably supply the voltage of the power supply stage to the filter unit, and is connected in series between the power supply terminal and the transistor to actively correspond to the output signals of the strong and weak electric fields of the phase comparator. Since it consists of a variable resistor for varying and applying a voltage and a grounded fourth capacitor connected in parallel between the variable resistor and the fourth resistor to bypass the high frequency components, the power supply voltage of the power supply terminal through the variable resistor of the voltage adjusting section. The weak electric field is adjusted so that it is properly applied to the base of the transistor through the fourth resistor. And a filter unit including the first, second, and third resistors and the first, second, and third capacitors, when outputting the strong electric field signal, so that the noise component output from the FM detection circuit can be properly adjusted, thereby capturing. There is an excellent effect that the critical level, which is related to the C / N ratio and the S / N ratio due to the range change, is further improved to obtain an optimum image quality.

Description

Loop Filter of FM Detection Circuit

The present invention relates to a loop filter of an FM detector circuit. In particular, when demodulating an FM modulated signal input to a tuner with an FM detector, the power supply voltage is varied so that the noise component is properly adjusted. The present invention relates to a loop filter of an FM detection circuit that further improves a threshold level having an N-to-S / N-ratio relationship to obtain an optimum picture quality when outputting a weak electric field signal.

In general, the FM detection circuit includes a phase comparator for comparing the frequency and phase of different signals input from the outside and generating an error voltage proportional to the result, and a loop filter for suppressing noise components included in the output signal of the phase comparator. And an oscillator for outputting an oscillation frequency in proportion to the control voltage output from the loop filter.

In this case, the FM detection circuit, when demodulating the video signal from the FM signal, if the C / N ratio is less than a certain value, the S / N ratio drops rapidly, where the C / N ratio of the point where the S / N ratio is 1 dB away Is called the threshold level, and as the threshold level increases, deterioration occurs and a clear screen cannot be obtained.

On the other hand, the C / N ratio represents the ratio of the FM signal and the noise signal at the input of the detection circuit, the S / N ratio represents the ratio of the video signal and noise signal at the output of the detection circuit.

The loop filter of the FM detection circuit according to the related art having the above configuration and function will be described with reference to FIG.

1 is a circuit diagram including a block diagram showing a loop filter of an FM detection circuit according to the prior art, where reference numeral 20 designates a loop filter and 40 designates a detection circuit.

As shown in FIG. 2, the loop filter 20 of the FM detection circuit 40 according to the related art compares the frequency and phase of different signals input from the outside to generate an error voltage proportional to the result. A filter unit 21 for filtering the output signal of the phase comparator 10 and a switching voltage of the power supply terminal B ⁺ so as to change the capture range by adjusting the noise component of the filter unit 21. It consists of a voltage regulator 22.

At this time, the filter unit 21 is connected in parallel with the first resistor R ₁₀ connected between the output terminal of the phase comparator 10 and the input terminal of the oscillator 30, and in parallel with the first resistor R ₁₀ . A second resistor R ₂₀ and a first capacitor C ₁₀ configured in series with each other and the phase comparator 10 and the second resistor R ₂₀ are connected to block a DC component of the voltage adjusting unit 22. It is sequentially connected between the coupled second capacitor (C ₂ o) and the oscillator 30 and the first capacitor (C ₁₀₎ for of a third capacitor for applying a switching voltage of the voltage control unit (22) (C ₃₀ ) And the third resistor R ₃₀ .

In addition, the voltage adjusting part 22 has a cathode connected to the third resistor R ₃₀ of the filter part 21 and an anode connected to the second capacitor C ₂₀ so that the switch of the power supply terminal B ⁺ is connected. A diode (D) for regulating the switching voltage applied by (S ₁ ), a grounded fourth resistor (R ₄₀ ) connected in parallel to the cathode of the diode (D), the switch (S ₁ ) and a diode ( D) connected between the fifth resistor R ₅₀ and the switch S ₁ and the fifth resistor R ₁₀ to apply the power supply voltage of the power supply terminal B ⁺ to the diode D. And a fourth capacitor C ₄₀ connected in parallel to bypass the high frequency component.

Referring to the operation of the loop filter 20 of the FM detection circuit 40 according to the prior art having the above configuration as follows.

First, when the power supply voltage of the power supply terminal B ⁺ is applied to the filter unit 21 through the fifth resistor R ₅₀ and the diode D by the on / off operation of the switch S ₁ , that is, voltage regulation. When the switching voltage by the operation of the unit 22 is applied to the third resistor R _{30 of the} filter unit 21, the first, second and third capacitors C ₁₀ and C of the filter unit 21 are used. ₂₀ ), (C ₃₀ ) and the first and second resistors R ₁₀ and R _{20 work} together to suppress the noise component included in the output signal of the phase comparator 10 to adjust the capture range. Make sure

However, the loop filter of the conventional FM detection circuit, in order to change the capture range of the FM detection circuit when the power supply voltage of the power supply terminal is applied, in the process of suppressing the noise component, the power supply voltage of the power supply terminal Since the switch is applied by the on / off operation, there is a big disadvantage in that the field intensity is supersaturated in different areas, especially in the weak electric field area, resulting in a change in image quality and inaccurate original screen.

Accordingly, the present invention has been made to solve the above-mentioned problems, the purpose of which is to control the noise component of the filter unit by driving the transistor in accordance with the supply of the power supply voltage of the power supply through the control of the variable resistor and At the same time, it expands the bandwidth of the capture range to raise the threshold level to provide a loop filter of the FM detector circuit that can supply a high quality output screen.

1 is a circuit diagram including a block diagram showing a loop filter of an FM detection circuit according to the prior art.

2 is a circuit diagram including a block diagram showing a loop filter of the FM detection circuit according to the present invention.

* Explanation of symbols for main parts of the drawings

10: phase comparator 20: loop filter

21 filter unit 23 voltage control unit

30: oscillator 40: detection circuit

B ⁺ : power stage C ₁ : first capacitor

C ₂ : Second Capacitor C ₃ : Third Capacitor

C ₄ : 4th capacitor R ₁ : 1st resistor

R ₂ : second resistor R ₃ : third resistor

R ₄ : fourth resistor S ₁ : switch

TR: Transistor VR: Variable resistor

The loop filter of the FM detection circuit according to the present invention for achieving the above object, the first resistor connected between the output terminal of the phase comparator and the input terminal of the oscillator, and the second resistor connected in parallel with the first resistor in series And a first capacitor, a coupling second capacitor connected between the phase comparator and the second resistor to block direct current components, and a third capacitor and a third resistor sequentially connected between the oscillator and the first capacitor. A loop filter of an FM detection circuit, comprising: a filter unit for suppressing a noise signal; and a voltage controller for applying a power supply voltage of a power supply terminal so that a capture range can be changed by adjusting a noise component of the filter unit. The control unit has an emitter grounded, a collector connected to the third resistor, and a base connected to the second capacitor. And a fourth resistor connected in series to stably supply the voltage of the power supply terminal to the filter unit, and connected in series between the power supply terminal and the transistor according to the output signals of the strong and weak electric fields of the phase comparator. And a variable resistor for actively applying a variable power supply voltage, and a grounded fourth capacitor connected in parallel between the variable resistor and the fourth resistor to bypass high frequency components.

Therefore, the loop filter of the FM detection circuit according to the present invention, the power supply voltage of the power supply terminal through the variable resistor of the voltage adjusting unit is properly adjusted to be applied to the base of the transistor through the fourth resistor, the weak field and the strong field signal output The filter unit composed of the first, second, and third resistors and the first, second, and third capacitors is interlocked to properly adjust the noise component output from the FM detection circuit. The threshold level, which is related to the / N ratio and the S / N ratio, is further improved to obtain an optimum image quality.

EXAMPLE

Hereinafter, a preferred embodiment of the loop filter 20 of the FM detection circuit 40 according to the present invention will be described with reference to FIG.

2 is a circuit diagram including a block diagram showing a loop filter of the FM detection circuit according to the present invention.

As shown in FIG. 2, the loop filter 20 of the FM detection circuit 40 according to the present invention compares the frequency and phase of different signals input from the outside to generate an error voltage proportional to the result. A filter unit 21 for filtering the output signal of the phase comparator 10 and a voltage controller 23 for applying a variable voltage so that the capture range can be changed by adjusting the noise component of the filter unit 21. Is done.

In this case, since the filter unit 21 is the same as the conventional configuration, it will be omitted for convenience, and the voltage adjusting unit 23, which is a key factor of the present invention, will be described as follows.

As shown in FIG. 2, the loop filter 20 of the FM detection circuit 40 according to the present invention which applies a variable voltage so that the capture range can be changed by adjusting the noise component of the filter unit 21 is changed. In the voltage adjusting unit 23, the emitter is grounded, the collector is connected to the third resistor R ₃ , and the base is connected to the second capacitor C ₂ , and at the same time, the fourth resistor R ₄ is connected. The transistor TR is connected in series to stably supply the voltage of the power supply terminal B ⁺ to the filter unit 21, and is connected in series between the power supply terminal B ⁺ and the transistor TR. A variable resistor (VR) for actively responding to the output signals of the strong and weak electric fields of the comparator 10 to vary the power supply voltage, and in parallel between the variable resistor (VR) and the fourth resistor (R ₄ ). A fourth grounded capacitor C ₄ connected to bypass high frequency components .

Referring to the operation and operation of the loop filter 20 of the FM detection circuit 40 according to the present invention by the above configuration as follows.

The first, second and third resistors R ₁ are applied to the power supply voltage (B ⁺ ) applied through the variable resistor VR to the base of the transistor TR through the fourth resistor R ₄ . Noise of the FM detection circuit 40 by the filter unit 21 composed of (R ₂ ), (R ₃ ) and the first and second and third capacitors (C ₁ ), (C ₂ ), and (C ₃ ). By properly adjusting the components, it is possible to further improve the threshold level, which is related to the C / N ratio and the S / N ratio due to the change of the capture range, to obtain the optimum image quality.

As described above, the loop filter of the FM detection circuit according to the present invention has a weak electric field and a strong electric field by allowing the power supply voltage of the power supply terminal through the variable resistor of the voltage adjusting unit to be properly adjusted and applied to the base of the transistor through the fourth resistor. When the signal is output, the filter unit composed of the first, second, and third resistors, and the first, second, and third capacitors are interlocked to properly adjust the noise component output from the FM detection circuit. By the C / N ratio and the S / N ratio of the critical level is further improved, there is an excellent effect that can obtain the optimum image quality.

Claims (1)

A direct current component connected between a first resistor connected between an output terminal of the phase comparator and an input terminal of the oscillator, a second resistor and a first capacitor connected in parallel with each other in parallel with the first resistor, and connected between the phase comparator and the second resistor; A second capacitor for coupling a circuit, a third capacitor and a third resistor sequentially connected between the oscillator and the first capacitor to suppress a noise signal, and to capture the filter through adjustment of a noise component of the filter unit. In the loop filter of the FM detection circuit including a voltage adjusting unit for applying a power supply voltage of the power supply terminal so that the range can be changed, the voltage adjusting unit, the emitter is grounded, the collector is connected to the third resistor, At the same time the second capacitor is connected and the fourth resistor is connected in series to filter the voltage of the power terminal A variable resistor that is stably supplied between the transistor and the power supply terminal and the transistor, the variable resistor being active in response to the output signals of the strong and weak electric fields of the phase comparator to vary and apply a power supply voltage; And a grounded fourth capacitor connected in parallel between the fourth resistor and bypassing the high frequency component.