JPH11340797A - Voltage-controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage-controlled oscillator whose temperature dependency of the oscillation frequency to an input voltage is relieved. SOLUTION: A voltage-current converter 1 converts the input voltage into a current. The current obtained by the voltage-current converter 1 is mirrored and supplied to a 1st and a 2nd current source. A voltage generator 2 has a band-gap circuit and generates a voltage given temperature dependency equal to that of the current after the voltage-current conversion by the voltage-current converter 1. An astable multivibrator 3 has its oscillation frequency determined according to the currents of the 1st and 2nd current sources, a capacitor C connected between the 1st and 2nd current sources and the operation amplitude across the capacitor C1 limited by the voltage generator 1. Consequently, the oscillation frequency to the input voltage does not have any temperature dependency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator oscillating at a wide frequency band in a semiconductor integrated circuit.

[0002]

2. Description of the Related Art An example of a conventional voltage controlled oscillator will be described with reference to FIG. This voltage controlled oscillator comprises a voltage-current converter 4 for converting an input Vin into a current corresponding to the voltage, a voltage generator 5, and a multivibrator 6. The voltage-current converter 4 includes an operational amplifier 4a, a transistor Q13, and a resistor R3 for converting a current into a voltage.
have. The converted current is applied to transistor Q11,
It is output as a converted current through the current mirror circuit composed of Q12. The voltage generator 5 has resistors R4 and R
5, a constant voltage is supplied to the multivibrator 6. The multivibrator 6 includes transistors Q1, Q2 for supplying a current equal to the current of the voltage-current converter 4 to the switching transistors Q2, Q8, respectively.
9 and Q10, and transistors Q1 and Q9 constitute first and second current sources. The multivibrator 6 has a transistor Q2
無 Q8 are symmetrically connected, and the emitter ends thereof are connected via a capacitor C1 to form an astable multivibrator.

The voltage Vin is input to the voltage-current converter 4 of the voltage controlled oscillator having the above configuration. The input voltage Vin is converted into a current by the voltage-current converter 4, mirrored by the current mirror, and supplied to the first and second current sources of the multivibrator 6. On the other hand, the voltage generator 5
, The transistor Q in the multivibrator 6
2, and a base voltage is supplied to the transistor Q8.
This voltage is an amplitude voltage for determining the operation amplitude of both ends of the capacitor C1 connected between the emitters of the transistor Q2 and the transistor Q8. In this oscillator, the voltage-
The current value of the first and second current sources supplied from the current converter 4, the capacitance of the capacitor C1 connected between the first and second current sources, and the amplitude voltage from the voltage generator 5 The oscillation frequency is determined.

Next, the operation of the voltage controlled oscillator will be described with reference to the operation waveform diagram of FIG. The initial values are such that the transistor Q3 is on and the transistor Q7 is off. As for the base voltage of the transistor Q8 and the transistor Q2, the H level is Vcc-2 * V _BE , and the L level is the voltage generator (R
5 / (R4 + R5)) * Vcc-2 * _VBE .
Therefore, the base amplitude of transistor Q2 and transistor Q8 is (R4 / (R4 + R5)) * Vcc, which is the voltage across resistor R4. Initial value is transistor Q
2 is at H level, and the base of transistor Q8 is at L level.
When the level is at the level, the transistor Q2 is on, the transistor Q8 is off, and the transistor Q8 side of the capacitor C1 is discharged by the current source supplied from the voltage-current converter 4, so that the emitter voltage of the transistor Q8 decreases. To go. When the emitter voltage of the transistor Q8 drops to a level at which the transistor Q8 can be turned on, that is, when the emitter voltage _drops to V _{BE with} respect to the base voltage of the transistor Q8, the transistor Q8 is turned on, and in order to draw current from the collector, The transistor Q7 is turned on, and the base of the transistor Q2 goes to L level. When the base of the transistor Q2 becomes L level, a reverse bias is applied between the emitter and the base of the transistor Q2, so that the transistor Q2 is turned off. No current flows to the collector of the transistor Q2, and the transistor Q3 is turned off.
Becomes H level. When the base voltage of the transistor Q8 goes high, the voltage at the emitter of the transistor Q8 also charges the capacitor and goes high, and at the same time the potential on the transistor Q2 side of the capacitor C1 is raised by the same amplitude. The reverse bias voltage between the base and the emitter of the transistor Q2 becomes twice the amplitude determined by the voltage generator, and discharge by the current source is started. When the emitter voltage of the transistor Q2 decreases to a level at which the transistor Q2 can be turned on,
The transistor Q2 turns on. This repetition is oscillation, and the oscillation frequency is determined by the cycle.

[0005]

However, in the conventional configuration described above, if the current after conversion with respect to the external input voltage Vin is Io in the voltage-current converter 4 in FIG. 4, Io is expressed by the following equation. . Io = Vin / R3

[0006] Here, the resistor R3 is a resistor for converting a voltage into a current, and has a temperature dependency. As a result, the current Io after the voltage-current conversion has a temperature dependency. Assuming that the voltage at both ends of the resistor R4 in the voltage generator 5 is Va, Va is represented by the following equation: Va = Vcc * (R4 / (R4 + R5)), and Va has a temperature dependency because it is determined by a resistance ratio. Absent. The oscillation frequency of the multivibrator 6 is determined by Io from the voltage-current converter 4, the voltage Va across the resistor R4 in the voltage generator 5, and the capacitance C1 of the capacitor C1, and is represented by the following equation, where f is the oscillation frequency. be able to. f = Io / (4 * Va * C1) Here, since Io has temperature dependency, the oscillation frequency with respect to the input voltage has temperature dependency, and it becomes difficult to widen the oscillatable frequency range. Had the disadvantage that

An object of the present invention is to solve the above-mentioned conventional problems and to propose a voltage-controlled oscillator in which an oscillation frequency with respect to an input voltage does not have temperature dependency.

[0008]

In order to achieve this object, a voltage controlled oscillator according to the present invention comprises: a voltage-current converter for converting an input voltage into a current; A voltage generator having a bandgap circuit for generating a voltage in accordance with the temperature dependence of the current, and a current mirror circuit for supplying a mirrored current to the current after the voltage-current conversion. 1st, 2nd
Current source, the output of the voltage generator is connected to each control terminal, one end is connected to the first and second current sources, a pair of switching elements that are turned on alternately, and the switching element and the A multivibrator having a capacitor connected between the first and second current sources.

With such a configuration, the oscillation frequency with respect to the input voltage does not have a temperature dependency, so that it is easy to oscillate in a wide frequency range.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of the voltage controlled oscillator according to the present embodiment. In FIG. 1, 1 is a voltage-current converter, 2 is a voltage generator, and 3 is a multivibrator. The voltage-current converter 1 and the multivibrator 3 are the same as the voltage controller 4 and the multivibrator 6 according to the above-described conventional example, and a detailed description thereof will be omitted. In this embodiment, the voltage generator 2 is not a resistance voltage dividing circuit,
Assuming that the temperature variation coefficient of the current Io supplied to the first and second current sources of the multivibrator 3 is t, a voltage Vb having a temperature variation equal to t is generated.

The operation of the thus-configured voltage controlled oscillator according to the present embodiment will be described below. When the voltage Vin is input to the voltage-current converter 1, the voltage is converted into a current. When the converted current is Io, the current is expressed as Io = Vin / R3 (1). The current Io thus converted is mirrored by a current mirror and supplied to first and second current sources including transistors Q1 and Q9. On the other hand, the base voltage amplitude of the transistor Q2 and the transistor Q8 in the multivibrator 3 is controlled by the voltage generator 2, and the emitter of the transistor Q2 and the transistor Q8 are controlled.
An amplitude voltage Vb for determining the operation amplitude at both ends of the capacitor connected between the emitters is generated. Also in this oscillator, the current values of the first and second current sources supplied from the voltage-current converter 1, the capacitance of the capacitor C1 connected between the first and second current sources, and the voltage generator 2 The oscillation frequency is determined based on the amplitude voltage from the input. The oscillation frequency f is expressed by the following equation. f = Io / (4 * Vb * C1) (2)

Here, the voltage generator 2 will be described with reference to the drawings. FIG. 2 is a circuit diagram of the voltage generator 2 according to the embodiment of the present invention. The voltage generator is configured using a band gap circuit. Here, the transistor size ratio of transistor Q17 to transistor Q20 is N
And That is, it is assumed that the transistor Q17 is configured by using N transistors of the same size as the transistor Q20. The base-emitter voltage V _BE20 of the transistor Q20 is determined by the current flowing through the resistors R10 and R8.
It is shown by the following formula as 1 and I2.

(Equation 1) The emitter voltage V1 of the transistor Q19 is expressed by the following equation.

(Equation 2) When V _BE20 = V _BE16, the following equation from the formula described above (5),
(6) holds.

(Equation 3)

(Equation 4) Therefore, the emitter voltage V1 is expressed by the following equation.

(Equation 5)

The bases of transistors Q19 and Q14
Assuming that the emitter-to-emitter voltages are equal, the transistor Q14
Is also V1, and the current flowing through the resistor R7 is V1 / R7. The voltage Vb at both ends of the resistor R6 is represented by Vb = V1 * R6 / R7 (8), and the temperature dependency of Vb is determined by V1.
That is, by adjusting the ratio between the resistors R8 and R9, the ratio between the resistors R8 and R10, and the size ratio N between the transistors Q10 and Q17, Vb can be made temperature-dependent. By making the voltage Vb have the same temperature dependency as Io, the oscillation frequency f determined by the equation (2) becomes less likely to have the temperature dependency.

Next, the operation of this circuit will be described using the operation waveforms shown in FIG. The initial values are such that the transistor Q3 is on and the transistor Q7 is off. Transistor Q
8 and the base voltage of the transistor Q2 is H level at Vcc.
-2 * V _BE , L level is Vcc-2 * when voltage generator 2 operates
It is given by V _BE -Vb. Therefore, the base amplitude of the transistor Q2 and the transistor Q8 is Vb, which is the limiting voltage of the voltage generator 2. The initial value of the transistor Q2
Is high and the base of transistor Q8 is low, transistor Q2 is on, transistor Q8 is off, and transistor Q8 of capacitor C1 is on.
The 8 side is discharged by the current source supplied from the voltage-current converter 1, and the emitter voltage of the transistor Q8 decreases. When the emitter voltage of the transistor Q8 drops to a level at which the transistor Q8 can be turned on,
That is, when the emitter voltage drops to V _{BE with} respect to the base voltage of the transistor Q8, the transistor Q8 is turned on, and the transistor Q7 is pulled to draw current from the collector.
Is turned on, and the base of transistor Q2 goes to L level. When the base of the transistor Q2 becomes L level, a reverse bias is applied between the emitter and the base of the transistor Q2, so that the transistor Q2 is turned off. No current flows to the collector of the transistor Q2, and the transistor Q3 is turned off. The voltage goes to H level. When the base voltage of the transistor Q8 goes high, the voltage at the emitter of the transistor Q8 also charges the capacitor C1 and goes high, and at the same time, the potential on the transistor Q2 side of the capacitor C1 is raised by the same amplitude. The reverse bias voltage between the base and the emitter of the transistor Q2 becomes twice the amplitude determined by the voltage generator 2, and the discharge by the current source is started. When the emitter voltage of the transistor Q2 decreases to a level at which the transistor Q2 can be turned on,
The transistor Q2 turns on. This repetition is oscillation, and the oscillation frequency is determined by the cycle.

As described above, according to the present embodiment, it is possible to make the oscillation frequency independent of the temperature with respect to the input voltage of the voltage-current converter.

[0016]

As described above, according to the present invention, the oscillation frequency with respect to the input voltage can be made independent of the temperature by providing the voltage source with a temperature fluctuation equal to the temperature fluctuation of the voltage-current converter. , It becomes easy to obtain a wide oscillation range.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a voltage controlled oscillator according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a voltage generator according to the present embodiment.

FIG. 3 is an operation waveform of the voltage controlled oscillator according to the present embodiment.

FIG. 4 is a configuration diagram of a conventional voltage controlled oscillator.

FIG. 5 is an operation waveform of a conventional voltage controlled oscillator.

[Explanation of symbols]

 1,4 voltage-current converter 2,5 voltage generator 3,6 multivibrator

Claims (1)

[Claims] 1. A voltage for converting an input voltage into a current.
The voltage-current converter, comprising: a current converter; a voltage generator including a band gap circuit that generates a voltage corresponding to the temperature dependence of the converted current in the voltage-current converter; and a current mirror circuit. The first, which supplies a mirrored current to the later current
A second current source, a pair of switching elements having outputs connected to respective control terminals, one end of which is connected to the first and second current sources, and which are alternately turned on; A multivibrator having a capacitor connected between the first and second current sources;
A voltage-controlled oscillator comprising: