JPH0119282B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the configuration of a voltage-controlled oscillator whose oscillation frequency can be controlled by an external voltage, and particularly to a detection circuit for an intermediate frequency video signal of a television receiver. The present invention provides an oscillator suitable for generating an oscillation signal synchronized with an input video carrier.

As means for detecting the intermediate frequency video signal of a television receiver, there is an envelope detection method using a diode, and a pseudo-synchronous detection method in which a video carrier is extracted by a tuned circuit and multiplied by the original signal.
Furthermore, there is a method such as a synchronous detection method that includes an oscillator that generates an oscillation signal that is synchronized with the video carrier and multiplies its output by the original input signal. Since the television signal is sent using the vestigial sideband communication method, the detection distortion that occurs is smaller in the latter case.
Although this produced good results in image and sound quality, it was not put into practical use because the circuit became complicated. However, recent integrated circuit devices have solved this problem and are about to be put into practical use.

FIG. 1 is a general block diagram of such a synchronous detection circuit. The input is passed through an intermediate frequency amplifier 1 to multipliers 2 and 3. Multiplier 3
is low-pass filter 4 and voltage-controlled oscillator (VCO)
Phase Locked Loop (RLL) with 5
An oscillation output synchronized with a phase orthogonal to the video carrier output from the intermediate frequency amplifier 1 can be obtained. By shifting the phase of this output by π/2 using the phase shifter 6 and applying it to the multiplier 2, a synchronously detected video signal can be obtained.

FIG. 2 shows a conventional example of a portion corresponding to the voltage-controlled oscillator 5 used in such a circuit, in which the current i of a constant current source is controlled as described in U.S. Pat. No. 4,071,832. By doing this, the magnitudes of components of different phases are changed, and the phase of the combined output is changed and applied to the oscillation amplifier circuit, thereby controlling the oscillation frequency. This has a simple configuration and can vary a considerable range centering on the resonant frequency between the coil and capacitor.

However, this method of controlling the current source current has drawbacks such as being vulnerable to power supply voltage fluctuations and increasing power consumption due to wide changes in current value, which is disadvantageous for integrated circuit devices. be.

Therefore, in the present invention, the synchronous detection circuit does not necessarily have π/2
Taking advantage of the presence of a phase shifter, we installed a π/2 phase shift circuit in the oscillator feedback circuit, and made the entire circuit configuration including the differential amplifier and phase shifter symmetrical. Therefore, the present invention aims to provide a device that is resistant to changes in temperature and power supply voltage by controlling the oscillation frequency, has less negative effects such as unnecessary radiation on other circuits, and consumes less power.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to drawings showing one embodiment thereof.

FIG. 3 shows a specific circuit diagram of an embodiment of the present invention, in which a differential amplifier is combined with a resonant circuit and a π/2 phase shifter to form an actual circuit. A resonant circuit consisting of a coil 9 and a capacitor 10 is connected between the collectors A and B of the first and second transistors 7 and 8 constituting the differential amplifier, which are connected with a common emitter, and the first get the output of

The collector of transistor 8 is connected to the base of transistor 7 via resistor 21, and capacitor 1 is connected to constitute a first π/2 phase shifter.
1 to the emitter of transistor 12. Since the base impedance of the transistor 12 is sufficiently low, the impedance of the emitter of the transistor 12 as seen from the capacitor 11 side is sufficiently low, so that the phase of the current supplied to the emitter of the transistor 12 through the capacitor 11 is that of the transistor 8. The collector current advances by π/2, and as a result, the output signal at terminal C advances by π/2. The same goes for the terminal D side, where the collector current of the transistor 7 similarly advances by π/2 due to the capacitor 13 and the transistor 14 that constitute the second π/2 phase shifter. After all, these capacitors 11,1
3 and transistors 12 and 14 constitute symmetrical first and second π/2 phase shifters, and a signal whose phase is advanced by π/2 from both ends of C and D than both ends of A and B is obtained. This is the second output.

The collector outputs, that is, the second outputs of the transistors 12 and 14 are connected to the common emitter and are applied to the bases of the third and fourth transistors 15 and 16, respectively, which constitute the differential amplifier.
Transistor 1 with common emitter connected
5th to 8th collectors connected to 5th and 16th collectors
In the transistors 17 to 20, the collectors of the fifth and seventh transistors 17 and 19 and the sixth and eighth transistors 18 and 20 are added and synthesized, and then the bases of the first and second transistors 7 and 8 are combined. is added to the signals at terminals A and B, and the signal is added and combined with the signals at terminals A and B, so that the total phase is changed. At this time, the transistors 15 to 20 constitute a double-balanced differential amplifier, and the ratio of the two signals to be synthesized at the collectors of the transistors 17 to 20 is determined from the terminals E and F to the transistors 17 and 2.
0 and the bases of the transistors 18 and 19 to control the phase of the combined output. As is clear from FIG. 3, this circuit is completely symmetrical.

FIG. 4 is a vector diagram explaining this situation. Let the voltage at terminal B be _VB , and its vector is shown on the diagram. As stated earlier, the voltage at terminal C V _C
advances V _B by π/2. Since the circuit is symmetrical, the voltages at terminals A and D are the voltages at terminals B and C, V _B ,
It also appears symmetrically with V _C on the vector. When the voltage at terminal E is sufficiently higher than that at F, transistors 17 and 20 are on and transistors 18 and 19 are off, so the summation current _i1 is equal to the current of transistor 15, and transistors 15 and 16 are used as differential amplifiers. Since the second outputs V _C and V _D are added to both bases, they are in phase with V _D as shown in the vector diagram. Since this current causes a potential drop at the resistor 21, the base voltage V ₁ of the transistor 7 is equal to V _B and i ₁ ×
It becomes a composite vector of the resistor 21, and if the resistor 21 is set to an appropriate value, it becomes a vector that lags _VB by π/4 as shown in FIG. By similar construction, the base voltage V ₂ of transistor 8 is determined by resistor 22.
It becomes a vector opposite to V ₁ .

These V ₁ and V ₂ are the transistor 7 of the differential amplifier,
8, and the collector voltages thereof become V _B and V _A . In that case, V ₁ and V ₂ must be
Since V _B and V _A must match, coil 9
Due to the phase shift between the resonant circuit of the capacitor 10 and the capacitor 10,
The phase is corrected and matches the original V _A and V _B . In order to correct the phase, the frequency is changed as shown in the frequency vs. phase φ characteristic of the resonant circuit in FIG. Therefore, the potential difference between terminals E and F is ΔV
When you change i ₁ becomes i ₁ ′, i ₁ ″, then
V ₁ also becomes V ₁ ′, V ₁ ″, and the phase angle θ changes from positive to negative, and the oscillation frequency can be changed from ₁ to ₁ ′ to ₁ ″ each time.

As described above, the voltage controlled oscillator of the present invention provides the following effects.

1. The frequency can be changed by voltage control, but the total current does not change, so current consumption can be lower than with conventional systems.

2. Since the circuit can be made symmetrical, there is less frequency drift due to changes in transistor characteristics. Furthermore, even if there is a fluctuation in the power supply voltage, it is less affected.

3. Can be constructed with circuits suitable for integrated circuit elements.

4. Because the circuit is symmetrical, the alternating current component of the total current flowing through the power supply and ground is zero, and the oscillation component does not leak to other circuits and cause adverse effects.

[Brief explanation of drawings]

Figure 1 is a block diagram of a general synchronous detection circuit.
FIG. 2 is a circuit diagram of a conventional voltage controlled oscillator, FIG. 3 is a circuit diagram of a voltage controlled oscillator according to an embodiment of the present invention, and FIGS. 4 and 5 are vector diagrams showing its operation and characteristics. It is a diagram. 7, 8... Differential amplifier transistor, 9, 10
...Resonant circuit coil and capacitor, 11, 12,
13, 14...Capacitor and transistor of π/2 phase shifter, 15-21...Transistor and resistance of amplitude and polarity adjustment circuit.

Claims (1)

[Claims] 1 a differential amplifier composed of first and second transistors 7 and 8 connected to a common emitter; a resonant circuit 9 and 10 connected between the collectors of the first and second transistors 7 and 8; Resistors 22 and 21 input the output signals of the collectors of the first and second transistors 7 and 8 to the bases of the other transistors 8 and 7, respectively, and the collectors of the first and second transistors 7 and 8, respectively. first and second phase shifters 11, 12, 13, and 14 having the same circuit configuration, which are connected to the respective collectors and shift the output signals of the respective collectors by π/2 to the same polarity; The output signals of the phase shifters 11, 12, 13, and 14 are inputted to their respective bases, and the differential amplifier is composed of third and fourth transistors 15 and 16, each of which is connected to a common emitter. and a differential amplifier composed of fifth and sixth transistors 17 and 18 whose common emitters are connected to the collector of the third transistor 15, and whose common emitters are connected to the collector of the fourth transistor 16. The seventh,
A double-balanced differential amplifier consisting of a differential amplifier constituted by an eighth transistor 19, 20, and the output signals of the collectors of the fifth and seventh transistors 17, 19 are combined, and the output signals of the collectors of the fifth and seventh transistors 17, 19 are combined. The circuit input to the base of No. 7, and the circuit input to the base of No. 7,
A circuit that combines the output signals of the collectors of the eighth transistors 18 and 20 and inputs them to the base of the second transistor 8, and the fifth and eighth transistors 17 and 20 and the sixth and seventh transistors 1.
A voltage-controlled oscillator comprising means for applying a control voltage for controlling the oscillation frequency between the bases of the voltage-controlled oscillator and the base of the voltage-controlled oscillator.