JPH118514A - Balanced oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a balanced oscillator, with which the number of parts is reduced, while maintaining a function for correcting an oscillation frequency based on an external voltage through an automatic fine tuning(AFT) voltage, for controlling that oscillation frequency. SOLUTION: This balanced oscillator has a signal amplifying means Tr1, a 1st resonance circuit, a signal amplifying means Tr2 and a 2nd resonance circuit. In order to vary the oscillation frequency through an external voltage VT and to correct this oscillation frequency through an AFT voltage, the balance oscillator provides this 1st resonance circuit with a variable capacitance diode Cv for impressing the external voltage VT and this 2nd resonance circuit with a variable capacitance diode Ca for impressing the AFT voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a balance oscillator used in a technology for receiving TV broadcasts and the like.

[0002]

2. Description of the Related Art In a communication field such as TV broadcasting, a high frequency signal called a carrier is modulated and transmitted in order to secure a large number of communication lines. Then, the receiving side performs selective reception from high-frequency signals of various frequencies, and reproduces the signals by demodulation.

For example, in TV broadcasting in Japan,
The video signal is modulated by AM (Amplitude Modulation)
The audio signal is modulated by FM (Frequency Modulation).
From 91.25 MHz assigned to each broadcasting station to 76
The signal is converted to a high-frequency signal up to 5.25 MHz and transmitted.

On the receiving side, as shown in FIG. 2, a signal received by an antenna 10 is selectively received by a band-pass filter 11 and amplified by an amplifier 12. And the mixer 13
And the local oscillation circuit 14 is used to temporarily convert the video signal to 58.7.
The audio signal is converted to 5 MHz and the audio signal is converted to 54.25 MHz.
The signal after this conversion is called an intermediate frequency signal. The local oscillation circuit 14 oscillates at a frequency 58.75 MHz higher than the frequency of the signal selected and received by the bandpass filter 11.

[0005] Thereafter, the intermediate frequency signal is amplified by the amplifier 15, and then the band pass filters 17 and 19 are distributed by the distributor 16.
To each other. The band-pass filter 17 passes the signal at a center frequency of 58.75 MHz, and the video demodulation circuit 18 reproduces the video signal. The band pass filter 19 allows the signal to pass at a center frequency of 54.25 MHz, and the sound demodulation circuit 20 reproduces the sound signal.

Various specifications are required for such a receiver to perform such reception. One of them is that the local oscillation circuit 14 obtains an accurate oscillation at a required frequency.

As shown in FIG. 3, in general, the oscillation circuit oscillates by taking out the required frequency component from the output of the amplifier 22 by the resonance circuit 23 and feeding it back positively. For example, a clap-type oscillation circuit often used in a high-frequency oscillation circuit is, as shown in FIG.
The capacitor Cce is inserted between the collector and the emitter of r3, the capacitor Cbe is inserted between the emitter and the base, and the capacitor Ccb and the coil L are inserted between the collector and the base in series.

As a result, the clap type oscillation circuit oscillates by amplifying the noise component generated in the power supply circuit and the like by the transistor Tr3 and positively feeding back the noise component in the resonance circuit formed by the capacitors Cbe, Cce, Ccb and the coil L.

The oscillation frequency f at this time is f = 1 / (2
× π × √ (L × C)). Where C is Cbe, C
It is a series combined capacitance of ce and Ccb. Further, the inductance L needs to be set to an appropriate value in a frequency range to be used.

In a local oscillator 14 (see FIG. 2) such as a TV receiver, a required oscillation frequency is obtained by changing a resonance frequency of the resonance circuit by an external voltage.
An oscillation circuit having such a function is connected to a voltage-controlled oscillator (V
CO). VCO (Voltage Controlled Oscillato)
In r), a varicap diode whose capacitance changes according to the value of the reverse voltage is used as the capacitance component of the resonance circuit, and the oscillation frequency is changed by changing the resonance frequency by the external voltage VT.

FIG. 5 shows the relationship between the external voltage VT and the oscillation frequency in such a VCO. As the magnitude of the reverse voltage increases, the capacitance value of the varicap diode decreases, and the oscillation frequency f tends to increase.

If the oscillation frequency deviates from the frequency required for generating the intermediate frequency signal, the intermediate frequency also naturally deviates in frequency, which greatly affects the reproduced video signal and audio signal. . Therefore, how to oscillate the oscillation frequency accurately is an important issue. Further, in general, the characteristics of the signal amplifying means such as the transistor Tr3 change depending on the external environment such as the temperature. As a result, there is a problem that the oscillation frequency changes.

Therefore, there is a case where an oscillation circuit is constituted by using a differential amplifier circuit which is strong against temperature change and also strong against in-phase noise. The oscillation circuit thus configured is called a balance oscillator. FIG. 6 shows an example of a conventional clap-type balance oscillator.

This balance oscillator is a VCO and has a configuration in which a clap type oscillation circuit shown in FIG. Capacitor Cc
e plays the role of both the capacitance Cce1 of the transistor Tr1 and the capacitance Cce2 of the transistor Tr2.
The coil L is also an inductor L1 on the transistor Tr1 side.
And the inductor L2 on the transistor Tr2 side.

Input terminal 2 for inputting external voltage VT
And is connected to the middle point of the coil L via the resistor Rv. The connection point between the capacitors Ccb1 and Cv1 is grounded via a resistor R1, and the connection point between the capacitors Ccb2 and Cv2 is grounded via a resistor R2. Varicap diodes Cv1 and Cv
Oscillation frequency changes because the capacitance value of No. 2 changes.

On the transistor Tr1 side, the oscillation frequency is determined by Cce1, Cbe1, Ccb1, Cv1 and inductance L1 forming a resonance circuit, and on the transistor Tr2 side, Cc1 forming another resonance circuit.
e2, Cbe2, Ccb2, Cv2 and inductance L
2 determines the oscillation frequency. Note that this circuit will be described again in the embodiment of the present invention.

In a TV receiver or the like, an AFT (Automatic Fi
Ne Tuning) circuit (not shown) may be used. The AFT circuit detects a frequency error when demodulating a video signal or an audio signal from the intermediate frequency signal, and uses the error as an AFT voltage as the local oscillation circuit 1.
4 (see FIG. 2) to correct the oscillation frequency.

As shown in FIG. 7, an input terminal 3 for inputting an AFT voltage to the balance oscillator is provided, and a varicap diode Ca is further added to the resonance circuit in the same manner as in the case where the oscillation frequency is varied by the external voltage VT. In addition, correction is performed by applying an AFT voltage to the varicap diode Ca. Note that this circuit will be described again in the embodiment of the present invention.

[0019]

By the way, in the above-mentioned conventional balance oscillator (FIG. 7), in addition to a function of varying the oscillation frequency by the external voltage VT, a function of correcting the oscillation frequency by the AFT voltage is added. There has been a problem that the number of parts is greatly increased.

The present invention solves the above-mentioned problems and provides an external voltage VT
It is an object of the present invention to provide a balance oscillator in which the number of components is reduced while maintaining the function of controlling the oscillation frequency by the AFT voltage and correcting the oscillation frequency by the AFT voltage.

[0021]

According to the present invention, a first signal amplifying means, a first resonance circuit, a second signal amplifying means, and a second resonance circuit are provided. Have
In a balance oscillator that varies an oscillation frequency with a first external voltage and corrects the oscillation frequency with a second external voltage, a first resonance circuit to which the first external voltage is applied is applied to the first resonance circuit. The varicap diode and the second resonance circuit include a second varicap diode to which the second external voltage is applied.

In such a configuration, since the capacitance value of the first varicap diode changes according to the first external voltage, the oscillation frequency of the entire balance oscillator can be varied. For example, when this balance oscillator is used for a local oscillation circuit of a TV receiver, A
By inputting the FT voltage as the second external voltage to the balance oscillator, the oscillation frequency can be corrected on the side of the second resonance circuit having the second varicap diode.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. As described above, FIG. 6 shows an example of the clap-type balance oscillator. In this circuit, the oscillation frequency can be varied by the external voltage VT, but the oscillation frequency cannot be corrected by the AFT circuit. Think again about making corrections possible.

The balance oscillator is configured to be axisymmetric like a differential amplifier circuit, and can be considered to be virtually grounded at a point on the axis of symmetry. Therefore, in the case of the circuit shown in FIG. 6, since it can be considered that each of the middle points of Cce and L is grounded, the capacitor Cce is connected to Cce1 and Cce2, and the coil L is connected to L1 and L2.
Are treated as if they were divided. That is, 1 /
Cce = 1 / Cce1 + 1 / Cce2, L = L1 + L2
It is.

The resistance components R1, R2, and Rv in the figure have an increased resistance value, and are therefore treated as open. Accordingly, it can be considered that the oscillation circuit is basically a combination of the two transistors Tr1 and Tr2 so that the oscillation circuits shown in FIG.

Based on the above premise, a comparison between the oscillation circuit shown in FIG. 6 and the oscillation circuit composed of one transistor Tr3 shown in FIG. 4 shows that the oscillation circuit shown in FIG. It can be seen that the capacitor is replaced with a combined capacitance of the capacitor Ccb1 and the varicap diode Cv1.

Therefore, on the transistor Tr1 side,
The oscillation frequency is L1, Cv1, Ccb1, Cbe1, Cbe1,
It is determined by ce1 and a parasitic capacitance component and an inductance component. The same can be said for the transistor Tr2. In the oscillation circuit shown in FIG. 4, the emitter is grounded, but in the oscillation circuit shown in FIG.
1, the collector of Tr2 is grounded, and the constant current source circuit 1 is connected to the emitter.

In order to further correct the oscillation frequency by the AFT circuit from the circuit shown in FIG. 6, capacitors Cbe1 and Cc
It is necessary to replace either b1 or Cce1 with a varicap diode. However, when replacing Cbe1 or Ccb1 with a varicap diode,
2 and Ccb2 also need to be replaced at the same time.

When Cce1 is replaced with a varicap diode, only Cce needs to be replaced.
Compared with the case where be1 or Ccb1 is replaced, only half the number of additional parts is required. Therefore, the one commonly used by both resonance circuits, such as Cce, is replaced.

FIG. 7 shows an example of a clap type balance oscillator in which Cce is replaced with a varicap diode. Here, the capacitor Cce in FIG. 6 is replaced with a combined capacitance of the capacitor Cce and the varicap diode Ca for correction. The input terminal 3 is connected to a connection point between Cce and Ca via a resistor Ra.
The input terminal 3 receives an AFT voltage from an AFT circuit (not shown). As a result, the capacitance of the varicap diode Ca changes according to the AFT voltage, so that the oscillation frequency can be corrected.

The conventional balance oscillator has been described above. Next, the balance oscillator according to the present embodiment will be described. FIG. 1 is a circuit diagram of the balance oscillator according to the present embodiment. NPN transistors Tr1 and Tr
The two collectors are both grounded. Transistor Tr1
A capacitor Cce is inserted between the emitter of the transistor Tr2 and the emitter of the transistor Tr2. Transistors Tr1, T
Capacitors Cbe1 and Cbe2 are connected between the base and the emitter for each of r2. Transistor T
r1 and Tr2 are signal amplification means.

The emitters of the transistors Tr1 and Tr2 are both connected to the constant current source circuit 1. Transistor Tr
The varicap diode Cv, the capacitor Ccb1, the coil L, the capacitor Ccb2, and the varicap diode Ca are connected so that the varicap diode Cv, the capacitor Ccb1, the coil L, the capacitor Ccb2, and the varicap diode Ca are sequentially connected in series from the base of the first transistor T1 to the base of the transistor Tr2.

The input terminal 2 is connected via a resistor Rv to a connection point between the varicap diode Cv and the capacitor Ccb1. An external voltage VT for changing the oscillation frequency is input to the terminal 2. The input terminal 3 is connected via a resistor Ra to a connection point between the varicap diode Ca and the capacitor Ccb2. An AFT voltage for correcting the oscillation frequency is input to the terminal 3.

The transistor Tr1 side of the varicap diode Cv is grounded via a resistor R1. The transistor Tr2 side of the varicap diode Ca is grounded via a resistor R2. As a result, the external voltages VT and AFT voltages are applied to the varicap diodes Cv and Ca, respectively. The resistance values of the resistors R1, R2, Rv and Ra are set high.

As described above, in this embodiment, the two varicap diodes C used in the circuit shown in FIG.
v1 or Cv2 is changed to Cv for changing the oscillation frequency.
The other is used for Ca for frequency correction. Therefore, there is no need to add a varicap diode.

In order for the VCO to exhibit the same function as the oscillation circuit shown in FIG.
It is necessary that the reactance component between the connection of the transistor and Tr2 be equal, so that the varicap diode C
v, Ca and Ccb1, L and Ccb2 are adjusted.

The oscillation frequency of the balance oscillator is Cc
e, Cbe1, Cbe2, Cv, Ccb1, L, Ccb
2. Determined by Ca. Thereby, the oscillation frequency is varied by the external voltage VT, and the oscillation frequency can be corrected by the AFT voltage from the AFT circuit.

According to the circuit of this embodiment, although the balance circuit is not completely symmetrical, the AF circuit
Even if the function of correcting the frequency from the T circuit is added, the number of components hardly increases, and there is a merit in cost as compared with the conventional balance oscillator (FIG. 7). Further, since the physical length of the resonance circuit can be made equal to the case where there is no correction by the AFT voltage, the AFT
There is an advantage that adverse effects such as deterioration of high-frequency characteristics due to an increase in parasitic elements, which usually become a problem when a circuit is connected, can be avoided.

Not only the clap-type balance oscillator but also a general balance oscillator using a differential amplifier circuit, one of the two resonance circuits varies the oscillation frequency by the external voltage VT, and the other resonates the AFT voltage. Thus, the oscillation frequency can be corrected, and the number of partial points can be reduced as described above. Although the case of the TV receiver has been described as an example, the balance oscillator of the present embodiment can be used where a VCO having an oscillation frequency correction function is used.

[0040]

As described above, according to the present invention,
While maintaining the functions of the balance oscillator and the AFT circuit, the number of components can be significantly reduced as compared with the conventional circuit (FIG. 7). In addition, the physical distance of the resonance circuit can be shortened, so that space can be reduced and high-frequency characteristics can be prevented from deteriorating.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a balance oscillator according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a demodulation mechanism of the TV broadcast receiver.

FIG. 3 is a block diagram illustrating the concept of an oscillation circuit.

FIG. 4 is a circuit diagram of a basic clap type oscillation circuit.

FIG. 5 is a characteristic diagram showing a relationship between an external voltage VT and an oscillation frequency f.

FIG. 6 is a circuit diagram of an example of a clap-type balance oscillator.

FIG. 7 is a circuit diagram of a conventional clap type balance oscillator with a correction function using an AFT voltage.

[Explanation of symbols]

1 constant current source circuit 2, 3 input terminal Tr1, Tr2 transistor Cv, Ca varicap diode R1, R2, Ra, Rv resistance Cce1, Cbe1, Cbe2, Ccb1, Ccb2
Capacitor

Claims (2)

[Claims] A first signal amplification unit, a first resonance circuit, a second signal amplification unit, and a second resonance circuit;
In a balance oscillator that varies an oscillation frequency with a first external voltage and corrects the oscillation frequency with a second external voltage, a first variator in which the first external voltage is applied to the first resonance circuit. A balance oscillator comprising: a cap diode; and a second varicap diode to which the second external voltage is applied to the second resonance circuit. 2. A first and second transistor having their collectors connected to each other; a constant current source circuit connected to both emitters of the first and second transistors; and an emitter of the first transistor. A first capacitor having both ends connected between an emitter of the second transistor, and a second and third capacitor connected between a base and an emitter of each of the first and second transistors; A first varicap diode, a fourth capacitor, a coil, a fifth capacitor, and a second varicap diode connected in series between the bases of both the first and second transistors; A first input terminal for introducing a first external voltage for varying an oscillation frequency between the first varicap diode and a fourth capacitor; A balance oscillator, comprising: a second input terminal for introducing a second external voltage for correcting the oscillation frequency, between the second varicap diode and a fifth capacitor.