JPH0969729A - Fm modulator with pll circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact FM modulator which excels in the stability of frequency and can secure a fast phase clock at the application time of a power supply without adding any circuit of an LPF, a switch, etc. SOLUTION: An FM modulator has a coupled circuit 3 between an active loop filter 2 constructing a PLL circuit and a VCO(voltage control oscillator) 4. The circuit 3 consists of a capacitor C1 , and resistors R1 and R2 . The control signals that undergone the voltage division through both resistors R1 and R1 , the DC bias power output and the video signal passed through the C1 are mixed together and applied to the VCO 4. Then the circuit 3 functions as an LPF that cuts off the comparison angular frequency ωref for the control signal of the PLL circuit and also functions as a DC cutter which eliminates the DC level variance for the video signal respectively. Furthermore, the DC bias power voltage is divided by a resistor and applied to the VCO 4, so that the initial value of voltage applied to the VCO 4 is equal to the value close to the voltage level that is set in a phase lock mode. At the same time, both control and video signals are mixed together at a high impedance and applied to the VCO 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM modulator to which a PLL (Phase Locked Loop) circuit for frequency stabilization is added, and particularly in a microwave / millimeter, which is strongly required to be small and lightweight, such as a wireless camera. The present invention relates to an FM modulator suitable for a waveband video transmission device.

[0002]

2. Description of the Related Art Conventionally, as an FM modulator having a PLL circuit for frequency stabilization, an FM modulator that is FM-modulated by a video signal in an intermediate frequency (IF) band (70 MHz, 130 MHz and the like is often used) is transmitted outdoors. It is used in devices.

Referring to FIG. 3 showing such a conventional FM modulator, the FM modulator includes a phase comparator 11, an active loop filter 12, a switch circuit 13, and
It includes a low pass filter 14, a coupling circuit 15, a voltage controlled oscillator (VCO) 16 and a frequency divider 17.
Natural angular frequency ω of the active loop filter 12
_n is set to be sufficiently small in order to avoid phase lock loss due to video signal level fluctuations, power supply fluctuations, and the like. On the other hand, such a setting lengthens the rise time required for the phase lock, so the switch circuit 13
By switching the natural angular frequency ω _n of the loop filter 12 at power-on and normal time, the rise time required for phase lock is shortened. Also, due to the leakage of the signal of the comparative angular frequency ω _ref component of the reference signal of the PLL circuit,
In order to avoid deterioration of the FM-modulated signal when viewed on the monitor screen, the low-pass filter 14 is used as necessary.
Is added.

[0004]

As described above, in the conventional technique as described above, in order to avoid the deterioration of the image due to the loss of the phase lock and to shorten the phase lock time at the time of turning on the power, the low frequency range is reduced. Since it is necessary to add circuits such as a pass filter and a switch, there is a problem to be solved that it is not suitable for miniaturization.

The present invention has been made in order to solve the above problems, and its purpose is to provide a compact and excellent frequency stability without adding a circuit such as a low-pass filter or a switch. P for fast phase lock at power on
It is to provide an FM modulator to which an LL circuit is added.

[0006]

In order to achieve the above object, the present invention provides an FM modulator for frequency-modulating a video signal, which includes a phase comparator, an active loop filter, a voltage controlled oscillator, and a frequency divider. A PLL circuit for frequency stabilization, comprising: a coupling circuit for mixing a control signal of the PLL circuit and a video signal between the active loop filter and the voltage controlled oscillator and adding the mixed signal to the voltage controlled oscillator; The coupling circuit has a DC bias power supply for applying a DC bias voltage to the voltage controlled oscillator so that the initial value of the voltage applied to the voltage controlled oscillator becomes a value near the voltage when the phase is locked, and the coupling circuit controls the control. As a low-pass filter that cuts off the comparative angular frequency for signals, a DC blocking circuit that eliminates DC level fluctuations for the video signals. As also for the DC bias voltage is acting as an output divider DC bias power source, characterized by mixing the DC bias power supply output said control signal and said video signal and.

In one form of the FM modulator of the present invention, the coupling circuit includes a capacitor C ₁ and first and second resistors R ₁ and R ₂ which are star-connected to each other. The input end of the resistor R ₁ is connected to the active loop filter, and the input ends of the capacitor C ₁ and the second resistor R ₂ are connected to the signal source of the video signal and the DC bias power source, respectively. , The capacitor C ₁ and the resistor R
The neutral point of the star connection of ₁ , R ₂ is connected to the input end of the voltage controlled oscillator, whereby the control signal divided by the resistors R ₁ , R ₂ and the output of the DC bias power supply and the It may be characterized in that the video signal having passed through the capacitor C ₁ is mixed and added to the voltage controlled oscillator.

Another form of the FM modulator of the present invention is as follows.
The natural angular frequency of the active loop filter is set to a value sufficiently smaller than the field angular frequency of the video signal, and the cutoff angular frequency of the coupling circuit is sufficiently smaller than the field angular frequency of the video signal. It may be set as a value sufficiently larger than the natural angular frequency.

In yet another form of the FM modulator of the present invention, the voltage controlled oscillator may be a microwave / millimeter wave band voltage controlled oscillator.

In the present invention, as described above, the FM modulator is constructed by adding the PLL circuit using the coupling circuit composed of, for example, the capacitor and the pair of resistors. This coupling circuit is PL
The control signal of the L circuit operates as a low-pass filter that blocks the comparative angular frequency ω _ref , and the video signal operates as a DC cutter (DC blocking circuit) that eliminates fluctuations in the DC level. In addition, the DC bias power supply voltage is divided by a resistor so that the initial value of the control signal becomes a value close to the voltage to be applied to the VCO when the desired oscillation frequency is generated.
By applying it to O, the time required for phase locking is shortened. Since this coupling circuit is used to mix the control signal and video signal with high impedance and add them to the VCO, it is compact and stable in frequency without adding a circuit such as a low-pass filter or switch to the active loop filter. It is possible to realize an FM modulator which is excellent in the degree and has a high-speed phase lock when the power is turned on.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a configuration example of an embodiment of an FM modulator to which the present invention is applied. This FM modulator includes a phase comparator 1, an active loop filter 2, and a coupling circuit 3.
And a voltage controlled oscillator (VCO) 4, a frequency divider 5 and a DC bias power supply 6. Describing according to the signal flow, a part of the FM modulation signal of the angular frequency ω _FM which is the output of the VCO 4 is divided by the frequency divider 5 by N (N is an integer),
It is converted into an FM modulated signal having an angular frequency of ω _FM / N. The phase comparator 1 compares the FM modulation signal of this angular frequency ω _FM / N with a reference signal of an angular frequency ω _ref (hereinafter referred to as a comparison angular frequency) supplied from a reference oscillator (not shown) such as a crystal oscillator. Then, a signal corresponding to the error in the frequency and the phase is output to the active loop filter 2. The active loop filter 2 removes high-frequency components such as abrupt changes in video level such as screen scene changes and circuit noise from the input signal, and the removed signal is used as an output voltage V _{lo op} in a coupling circuit. Add to 3.

The coupling circuit 3 comprises a capacitor C ₁ and first and second resistors R ₁ and R ₂ which are star-connected to each other.
The input end of the first resistor R ₁ is connected to the active loop filter 2, and the input ends of the capacitor C ₁ and the second resistor R ₂ are connected to the video signal source and the DC bias power source 6, respectively. . The neutral point of the star connection of the capacitor C ₁ and the resistors R ₁ and R ₂ is connected to the input terminal of the voltage controlled oscillator 4. As a result, the control signal divided by the _two resistors R ₁ and R ₂ of the coupling circuit 3, the output of the DC bias power source 6 and the video signal that has passed through the capacitor C ₁ are mixed and the voltage V _{v is obtained.} Is added to VCO4.

The active loop filter 2 described above is
It has a normal configuration including an operational amplifier (op amp), a resistor and a capacitor, and its output voltage V _loop becomes zero voltage when the power is turned on. Natural angular frequency ω _n of the active loop filter 2 (This is the vibration angular frequency when it is assumed that the PLL circuit vibrates by the loop filter and the loop gain, and is the most important parameter when designing the loop filter. 1)), so that the control of the PLL circuit follows a rapid level change of the video signal and the like, so that the video signal does not deteriorate when the FM modulation signal is viewed on the monitor screen. Is set to a value sufficiently smaller than the field angular frequency ω _F (= 60 Hz × 2 × π).

The coupling circuit 3 serves as a high-pass filter that cuts off the DC component from the video signal by the capacitor C ₁ and removes the influence of the fluctuation of the DC level, and the resistor R
₁ and R ₂ and the capacitor C _{1 function} as a low-pass filter that sufficiently blocks the comparative angular frequency ω _ref component with respect to the control signal input from the active loop filter 2.

Cutoff angular frequency ω _c (=
C ₁ × R ₁ × R ₂ / (R ₁ + R ₂ )) is sufficiently smaller than the field angular frequency ω _F of the video signal, but is sufficiently larger than the natural angular frequency ω _n (ω _n <<<< ω _c <
<Ω _F ) is set so that the circuit does not affect the loop filter. In addition, since the natural angular frequency ω _{n is set} to a very small value, it usually takes a considerable time to lock the phase when the power is turned on. However, due to the resistors R ₁ and R ₂ of the coupling circuit 3, the DC voltage is increased. The bias power supply voltage V ₁ is divided, and the initial value V _vo of the voltage V _v applied to the VCO 4 (this is the voltage when the PLL circuit has not started after the power is turned on, and is the voltage of the active loop filter 2 when the power is turned on. Since the output voltage V _loop is a zero voltage, V _vo = R ₁ × V ₁ / (R ₁ + R ₂ )) is selected so as to be a value near the voltage when the phase is locked. The phase lock time at the time of is shortened.

Next, the operation of the FM modulator of FIG. 1 according to the present invention will be described in more detail using the equivalent circuit shown in FIG.

As for the DC signal, as shown in FIG. 2A, the control signal of the PLL circuit and the DC bias power supply voltage V ₁ are divided by resistors R ₁ and R ₂ to be added to VCO 4. By selecting the resistance values of the resistors R ₁ and R _{2 and} the voltage value of the DC bias power supply voltage V ₁ so that the voltage of the control signal is phase locked at almost zero voltage, the phase lock time at power-on can be shortened. There is.

As for the AC signal, as shown in FIG. 2B, the video signal is passed through the internal impedance Z _g to VC.
It becomes a circuit added to O4.

Therefore, with the above-mentioned configuration, the FM modulator is small in size, has excellent frequency stability, and has a high-speed phase lock when the power is turned on, without adding a circuit such as a low-pass filter or a switch. Can be realized.

[0021]

[Embodiment] The FM modulation system which directly modulates in the microwave / millimeter wave band is a signal in which a signal modulated in the IF band is converted into a desired microwave / millimeter wave band.
Compared to the FM modulation method for converting to a frequency in the millimeter wave band, a mixer for frequency conversion, an oscillator or a multiplier, a filter, etc. are not necessary, and parts are reduced due to higher frequencies, It has the feature of being extremely compact. Therefore, by constructing an FM modulator that directly modulates in the microwave / millimeter wave band by combining the microwave / millimeter wave band VCO and the above-described coupling circuit according to the present invention, a small size and higher performance can be realized. .
For example, in an experiment with an FM modulator using a 14 GHz band VCO, the resistors R ₁ and R ₂ are about 50 kΩ, the capacitor C ₁ is about 3.3 μF, and the DC bias power supply voltage V ₁ is about -8 V. The results were obtained.

(Modification) The above-described coupling circuit according to the present invention is configured in an analog form using the capacitor C ₁ and the resistors R ₁ and R ₂ , but the present invention is not necessarily limited to this, and the above-mentioned Other circuit configurations that achieve similar functions are also included. For example, the target FM modulator can be constructed by applying the present invention to a digital PLL circuit.

[0023]

As described above, according to the present invention,
For example, a coupling circuit composed of one capacitor and two resistors is used, and this coupling circuit is used as a low-pass filter that cuts off the comparative angular frequency ω _ref for the control signal of the PLL circuit.
The video signal is operated as a DC cutter that eliminates the fluctuation of the DC level, and the control signal and the video signal are mixed with high impedance and added to the VCO.
The DC bias power supply voltage is divided by the above two resistors and applied to the VCO so that the initial value of the voltage applied to VCO becomes a value near the voltage when the phase is locked. Since it has been shortened, it is possible to realize an FM modulator that is small in size, has excellent frequency stability, and has high-speed phase lock at power-on, without adding a circuit such as a low-pass filter or a switch to the active loop filter. The effect is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an embodiment of an FM modulator to which the present invention is applied.

FIG. 2A is a circuit diagram showing an equivalent circuit for a DC signal of the FM modulator of the present invention, and FIG. 2B is an FM circuit of the present invention.
It is a circuit diagram which shows the equivalent circuit with respect to the alternating current signal of a modulator.

FIG. 3 is a block diagram showing a configuration example of a conventional FM modulator.

[Explanation of symbols]

 1 Phase Comparator 2 Active Loop Filter 3 Coupling Circuit 4 Voltage Controlled Oscillator (VCO) 5 Frequency Divider 6 DC Bias Power Supply 13 Switch Circuit 14 Low Pass Filter

Claims (4)

[Claims] 1. An FM modulator for frequency-modulating a video signal, comprising a phase comparator, an active loop filter, a voltage-controlled oscillator, and a frequency divider for P frequency stabilization.
An LL circuit, a coupling circuit for mixing a control signal of the PLL circuit and a video signal between the active loop filter and the voltage controlled oscillator and applying the mixed signal to the voltage controlled oscillator, and an initial voltage applied to the voltage controlled oscillator. A DC bias power supply for applying a DC bias voltage to the voltage controlled oscillator so that the value becomes a value near the voltage when the phase is locked, and the coupling circuit cuts off the comparative angular frequency for the control signal. It operates as a low-pass filter, as a DC blocking circuit for eliminating DC level fluctuations for the video signal, and as an output voltage dividing circuit of a DC bias power supply for the DC bias voltage, and outputs the control signal and the video signal. An FM modulator characterized by mixing the output of the DC bias power supply. 2. The coupling circuit includes a capacitor C ₁ and first and second resistors R ₁ and R ₂ connected in a star shape to each other, and an input terminal of the _first resistor R ₁ is the active terminal. Type loop filter, and the input ends of the capacitor C ₁ and the second resistor R ₂ are connected to the signal source of the video signal and the DC bias power source, respectively, and the capacitor C ₁ and the resistor R ₁ , The neutral point of the star connection of R ₂ is connected to the input of the voltage controlled oscillator, which causes the resistors R ₁ , R
_{2. The} voltage-controlled oscillator according to claim 1, wherein the control signal divided by ₂ and the output of the DC bias power supply and the video signal passing through the capacitor C ₁ are mixed and added to the voltage controlled oscillator. FM modulator. 3. A natural angular frequency of the active loop filter is set to a value sufficiently smaller than a field angular frequency of the video signal, and a cutoff angular frequency of the coupling circuit is set to be lower than a field angular frequency of the video signal. The FM modulator according to claim 1 or 2, wherein the FM modulator is set as a value sufficiently smaller than the natural angular frequency. 4. The voltage controlled oscillator is a microwave / millimeter wave band voltage controlled oscillator.
4. The FM modulator according to any one of 3 to 3.