JPH0222903A - Vco - Google Patents

Abstract

PURPOSE:To obtain an oscillation signal having stable level and frequency throughout a wide frequency range by connecting a phase advancing circuit, an amplifying transistor TR, and a by-pass capacitor to a resonance circuit. CONSTITUTION:A phase advancing circuit 3, an amplifying TR Q4, and a by-pass capacitor C3 are connected to a resonance circuit 2 of an oscillating circuit in prescribed relations. Consequently, since the oscillation current whose phase is advanced in comparison with the oscillation voltage flows at the time of viewing the phase advancing circuit 3 and the TR Q4 from the resonance circuit 2, the phase advancing circuit 3 and the TR Q4 acts as a capacity equivalently when viewed from the resonance circuit 2. That is, circuits added to the resonance circuit 2 act as a variable equivalent capacity. Thus, the oscillation frequency is stably changed throughout a wide frequency range up to a high frequency when the capacitor C3 is set to a prescribed small capacity.

Description

[Detailed description of the invention] [Industrial application field] This invention relates to a VCO.

[Summary of the invention]

The present invention provides a vCO in which an oscillation signal with stable level and frequency can be obtained over a wide frequency range by connecting a phase advancing circuit, an amplifying transistor, and a bypass capacitor to the resonant circuit.

[Conventional technology]

Vctb is required when performing AFC in an FM receiver or in a synthesizer type receiver.

When configuring such a CO, there are methods such as using a variable capacitance diode in the resonant circuit, or using a variable gain amplifier having a Miller effect.

[Problem to be Solved by the Invention] However, when using a variable capacitance diode, when trying to widen the variation range of the capacitance of the variable capacitance diode in order to widen the variation range of the oscillation frequency, the variation range of the control voltage It is necessary to widen the

However, in order to widen the variation range of the control voltage, the power supply voltage needs to be high, and it cannot be passed through a receiver that operates on a low voltage, for example, a single 1.5-inch AA battery.

Furthermore, when a variable capacitance diode is used, the linearity of frequency change with respect to the control voltage as vCO is not very good.

On this point, when using a variable gain amplifier with a Miller effect, it can be integrated into an IC and the required frequency variable range can be obtained with a low voltage, and the linearity of frequency change with respect to the control voltage as a VCO can be achieved. is better than that of a variable capacitance diode.

However, in order to widen the range of change in equivalent capacitance due to this Miller effect, it is necessary to increase the maximum gain of the variable gain amplifier to widen the range of gain change. In order to increase the maximum gain, the mutual conductance of the variable gain amplifier or the transistors that make up this amplifier must be increased, and to do so, the operating current must be increased, so the current consumption must be increased. It will increase.

This invention attempts to eliminate the above-mentioned problems.

[Means to solve the problem]

Therefore, in the present invention, a phase advance circuit, an amplification transistor, and a bypass capacitor are connected to the resonant circuit of the oscillation circuit in a predetermined relationship.

[Effect]

A circuit added to the resonant circuit acts as a variable equivalent capacitance.

〔Example〕

In FIG. 1, the emitters of transistors Q1*Q2 are commonly connected, and between this emitter and ground, the collector and emitter of transistor Q3 for a constant current source is connected to form a differential amplifier (1). Ru. Further, the collector of the transistor Q1 and the base of the transistor Q2 are connected to the power supply terminal TL, the base of the transistor QL is connected to the collector of the transistor Q2, and a capacitor C1 and a coil L1 are connected between this connection point and the terminal T. A parallel resonant circuit (2) having a parallel resonant circuit (2) is connected.

Further, a capacitor c2 is connected between the collector of the transistor Q2 and the base of the transistor Q4, and a resistor mRt is connected between the base and the terminal T1 to form a phase advancing circuit (3). Further, the transistor Q4 constitutes a variable reactance circuit (4) together with the phase advancing circuit (3), and its collector is connected to the collector of the transistor Q2, and a constant current is connected between the emitter of the transistor Q4 and the ground. Transistor QS for source
The collector-emitter of the resistor R5 is connected in series with the resistor R5.

Further, a phase compensation capacitor C3 is connected between the emitter of the transistor Q4 and the terminal TL.

Further, the base of the transistor Qε is connected to the control terminal T2 to be supplied with the control voltage Ec of the oscillation frequency, its emitter is grounded, its collector is connected to the terminal T1 through the resistor R3, and the base of the transistor Qs connected to.

Further, an oscillation output is taken out from the collector of transistor Q2, for example. Further, in the case of the VHF band, the capacitor C3 is about 20 pF.

According to such a configuration, when an AC signal component is obtained at the collector of the transistor Q2, this signal component is transmitted from the collector of the transistor Q2 to the base of the transistor Q1 to its emitter to the transistor Q2'? The D emitter receives positive feedback through its collector loop. At this time, if the resonant impedance of the resonant circuit (2) is sufficiently large, the loop gain of the positive feedback loop becomes sufficiently large at that resonant frequency, and oscillation occurs at that resonant frequency.

Furthermore, in this case, the oscillation voltage obtained on the hot side (collector of transistor Q2) of the resonant circuit (2) is phase-advanced by the phase-advancing circuit (3) and then supplied to the base of the transistor Q4. The voltage is converted to current and the current is amplified to form a resonant circuit (2)
Flows on the hot side of the.

Therefore, when looking at the phase advance circuit (3) and transistor Q4 from the resonant circuit (2), an oscillation current whose phase is advanced with respect to the oscillation voltage flows. ) and transistor Q4 equivalently act as a capacitor. In other words, the phase advancing circuit (3
) and transistor Q4 are capacitive reactance circuits (
This means that it is acting as 4. Therefore, the oscillation frequency of this circuit is determined by the element Ct@L1 and the equivalent capacitance C4 of the reactance circuit (4).

Then, when the control voltage Ec changes, for example, becomes lower, the collector current 1 of the transistor Q5 corresponds to the change.
5 increases, and the gain of transistor Q4 becomes thicker (although,
If the gain of the transistor Q4 increases, the oscillation current flowing through the resonant circuit (2) due to the transistor Q4 will increase, that is, the oscillation current will increase in the reactance circuit (4) even if the oscillation voltage is constant.
This is equivalent to an increase in the equivalent capacitance C4 of the actance circuit (4).

Therefore, the reactance circuit (4) operates as a variable reactance circuit whose equivalent capacitance C4 changes according to the control voltage Ec, and the oscillation frequency of this oscillation circuit changes according to the control voltage Ec. That is,
This oscillation circuit is a VCO whose oscillation frequency changes depending on the control voltage Ec.

〔Effect of the invention〕

Thus, according to the invention, a VCO can be obtained, but in this case, in particular, according to the invention, the power supply terminal T1
Since there is one collector-emitter and one base-emitter of the transistor stacked between the 3 batteries are part 6
It operates almost normally even when the voltage drops to 0%, and can operate even at extremely low voltages. Moreover, it is easy to implement it into an IC.

Furthermore, since the equivalent capacitance C4 of the variable reactance circuit (4) with respect to the collector current 15 of the transistor Qs is approximately linear as shown in FIG. 2, the linearity of the frequency change with respect to the control voltage Ec is Better than the case.

Additionally, in general, as the operating frequency of a transistor increases, a phase lag occurs, and therefore this VC
Also in O, when the oscillation frequency increases, a phase lag occurs in the transistor Q4, and this phase lag cancels out a part of the phase advance amount by the phase advance circuit (3). However, when the oscillation frequency is high, Then, the amount of negative feedback of the current applied to the transistor Q4 by the transistor Q5 is reduced by the capacitor C3, so that the gain of the transistor Q4 increases and the oscillation current flowing through the transistor Q4 increases.

If this oscillation current increases, the equivalent capacitance of the reactance circuit (4) increases (and the amount of phase advance increases, thereby canceling the phase lag of the transistor Q4. Therefore, the capacitor C3 is If the capacitance is small, the oscillation frequency can be varied over a wide frequency range up to high frequencies.At this time, as in the case of a variable gain amplifier with a Miller effect, the operating current (collector current Ig of transistor Q5) There is no need to increase the current consumption, and the current consumption can be reduced.

Furthermore, when the collector current I6 of the transistor Qs increases, the equivalent capacitance C4 increases and the oscillation frequency decreases, but at the same time, the reactance circuit (equivalent resistance R4 of
becomes small, and as a result, the above-mentioned loop gain in the differential amplifier (1) becomes small, and the oscillation level becomes weak. However, by setting the capacitor C3 to 1/(2πfc3)'qre (sin), the equivalent i-low resistance 4 can be increased to increase the equivalent Q, as shown by the broken line in Figure 2, and as a result, the oscillation You can increase the level.

Furthermore, as shown in FIG. 1, in an oscillation circuit in which a differential amplifier (1) is provided with a positive feedback loop and a resonant circuit (2), generally when the current voltage +Vcc becomes high, for example, the collectors of transistors Qz and Q2 The stray capacitance of vCO becomes smaller and the oscillation frequency becomes higher, but in this vCO,
When the current voltage +Vcc increases, the base potential of the transistor Qs rises and its collector current increases, and as a result, the equivalent capacitance c4 increases, making it possible to cancel the increase in the oscillation frequency due to the decrease in stray capacitance.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram of an example of the present invention, and FIG. 2 is a diagram for explaining the same. (1) is a differential amplifier, (2) is a parallel resonant circuit, (3) is a phase advancing circuit, and (4 is a variable reactance circuit).

Claims (1)

[Claims] 1. The emitters of the first and second transistors are connected to a constant current source to configure a differential amplifier, and the base of the first transistor is connected to the collector of the second transistor. At the same time, a parallel resonant circuit is connected between the collector of the second transistor and the power supply terminal to form an oscillation circuit, and the oscillation voltage obtained in the parallel resonant circuit is applied to the third transistor through the phase advance circuit. The collector output of this third transistor is supplied to the parallel resonant circuit, and a phase compensation capacitor is connected to the emitter of the third transistor to control the emitter current of the third transistor. A VCO that controls the oscillation frequency of the oscillation circuit. 2. The emitters of the first and second transistors are connected to a constant current source to configure a differential amplifier, the base of the first transistor is connected to the collector of the second transistor, and the second A parallel resonant circuit is connected between the collector of the transistor and the power supply terminal to form an oscillation circuit, and the oscillation voltage obtained from the parallel resonant circuit is supplied to the base of the third transistor through the phase advance circuit. The collector output of the third transistor is supplied to the parallel resonant circuit, a phase compensation capacitor is connected to the emitter of the third transistor, and the fourth transistor is base biased by the power supply voltage of the power supply terminal. , a control signal passes through the fourth transistor to the third transistor.
A VCO that is supplied to the emitter of the transistor to control the oscillation frequency of the oscillation circuit.