JPH09121143A - Temperature compensated variable frequency oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently components the influence of temp. in the temp. coefficient of an oscillation frequency by setting the current density of a reference diode to be lower than the that of a clamp diode and generating the temp. coefficient of the reference diode more largely. SOLUTION: When slight current is permitted to flow between a control input terminal 1 and a ground with starting resistance, the current is supplied to the composite circuit of the input TRs Q7 and Q8 of an oscillator 10 with the transistors TRs Q14 and Q15 off a current mirror stage and the operation current of the oscillator is supplied to TRs Q5 and Q6 constituting a constant current circuit. The current is permitted to flow through reference diodes Q91-Q9n so as to generate a forward lowering voltage VD. A differential voltage AMP amplifies the difference voltage between the forward lowering voltage VD and the terminal voltage of resistance R3, thereby current is permitted to flow through resistance R3 is increased through TR Q12 and Q13 so that the difference voltage becomes zero. Thus, the current density of the reference diode is set to be lower than that of the clamp diode so that the temp. coefficient of the reference diode is generated more largely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature-compensated variable frequency oscillator using an emitter-coupled multivibrator, and more particularly to a temperature-compensated variable frequency oscillator suitable for improving temperature characteristics of oscillation frequency.

[0002]

2. Description of the Related Art Generally, the oscillation frequency fo of a variable frequency oscillator using an emitter-coupled multivibrator is given by
It is represented by

[0003]

(Equation 1)

However, I1 is the current, C is the timing capacitor, and Vd is the forward voltage drop of the clamp diode.

The temperature coefficient of fo is as follows.

[0006]

(Equation 2)

Therefore, it depends on the temperature coefficient of the forward drop voltage Vd of the clamp diode. In order to eliminate this temperature effect, I1 of equation 1 is generated by linking it with the forward voltage drop Vd of the clamp diode. Therefore, temperature compensation is performed by using a method in which a reference diode having the same current density as the clamp diode is provided and I1 is generated based on the forward drop voltage of the reference diode. An example of this type of temperature-compensated variable frequency oscillator is, for example, "Bipolar and Moss Analog Integrated Circuit Design" by AVI Greben, (1984),
Pages 575 to 581, John Willy and Sons (ABGREBENE, BIPOLAR AND MOSANALOG INTEGR
ATED CIRCUIT DESIGN, (1984), pp.575-581, John Wiley
& Sans Inc.) and JP-A-62-224110.

[0008]

In the above-mentioned conventional example, a reference diode having the same current density as the clamp diode is provided in series with the emitter-coupled multivibrator to improve the temperature characteristic of the oscillation frequency fo. Regardless, the temperature effect of the oscillation frequency fo is not sufficiently compensated.
It is considered that the reason for this is that when the diode is used for the switching operation, the effective temperature coefficient of the diode is larger than that when it is used for the DC operation. that is,
The switching operation causes an increase in the base resistance of the transistor used as a diode, which apparently reduces the forward voltage drop of the diode, and thus the temperature influence becomes large. Normally, the temperature coefficient of the clamp diode for switching operation is several hundred ppm in absolute value with respect to the temperature coefficient of the reference diode for DC operation.
The temperature compensation type variable frequency oscillator with sufficiently high temperature stability is used as a temperature compensation type variable frequency oscillator by the method of matching the current density of the reference diode and the clamp diode used in the conventional temperature compensation method. There was a problem that I could not get it.

An object of the present invention is to provide a temperature-compensated variable frequency oscillator that can obtain a highly stable oscillation frequency that is not affected by temperature.

[0010]

To achieve the above object, the present invention provides a bias current having a transistor pair of positive feedback connection, a clamp diode, a timing capacitor, an emitter-coupled multivibrator having a constant current circuit, and a reference diode. In a temperature-compensated variable frequency oscillator including a generation circuit, by setting the current density of the reference diode lower than the current density of the clamp diode, the forward drop voltage VD of the reference diode is smaller than the forward drop voltage Vd of the clamp diode. Generate
The current generated based on this is used as the operating current of the constant current circuit.

According to this method, since the current density of the reference diode is set lower than the current density of the clamp diode, the forward drop voltage VD of the reference diode becomes small. The temperature coefficient generated in the reference diode is 1 / VD.
Since (dVD / dT), the temperature change of VD (dVD / d
Assuming that T) is almost constant, the temperature coefficient of the reference diode increases as VD decreases. As a result, the temperature coefficient of the clamp diode, which is large in the switching operation, is the same in absolute value as the temperature coefficient of the oscillation frequency.
Can be sufficiently compensated with the temperature coefficient of the reference diode that is set to a lower value than the clamp diode (the temperature coefficient of both is matched), so an oscillation frequency with good temperature stability as a temperature-compensated variable oscillator Can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, 10 is an oscillator, 20 is a bias current generating circuit for setting the frequency of the oscillator, 30 is a clamp diode section, and 40 is a reference diode section. The oscillator 10 includes a pair of switching transistors Q1 and Q2 connected alternately, pull-up resistors R1 and R2 connected to the collectors thereof, clamp diodes D1 and D2, transistors Q5 and Q6 forming a constant current circuit.
Timing capacitor C for integration, output terminals 2 and 3, and transistors Q3 and Q that operate as emitter followers for driving the bases of switching transistors Q1 and Q2.
4 and a transistor Q1 for controlling the bias current thereof
It consists of 0 and Q11. The oscillator 10 is known as an emitter-coupled multivibrator. The oscillation frequency of the oscillator 10 is controlled by a composite circuit of the transistors Q7 and Q8 connected to operate as the primary side of the constant current circuit composed of the transistors Q5 and Q6. The emitter currents of the transistors Q1 and Q2 and the timing capacitor C Depends on the value of. The frequency is basically represented by the above-mentioned mathematical expression 1.

The bias current generating circuit 20 includes an oscillator 10
A plurality of reference diodes Q91 to Q9n (transistors are used in diode connection) connected in parallel for detecting the clamp voltage of the oscillator equivalently, and a resistor R3 for setting the oscillation frequency. A differential amplifier AMP that amplifies the difference voltage between the reference diodes Q91 to Q9n and the resistor R3, a composite circuit of transistors Q12 and Q13 for supplying a current to the resistor R3, and a transistor Q14 that receives the current flowing through the setting resistor R3 as an input.
And a current mirror stage of base current compensation consisting of Q15 and Q16. The output of this current mirror stage is connected to the composite circuit of the input transistors Q7 and Q8 of the current mirror circuit of the oscillator 10. The terminal 1 of the bias current generating circuit 20 is a control input terminal for adjusting the control current with respect to the set value.

The operation of the circuit of FIG. 1 constructed as above is as follows. When a very small current (1 μA or less is allowed) is flown between the control input terminal 1 and the ground through a starting resistor (not shown), this current is applied to the transistor Q1 of the current mirror stage.
4, an input transistor Q7 of the oscillator 10 via Q15
And Q8, and supplies the operating current of the oscillator to the transistors Q5 and Q6 which form a constant current circuit.
The operating current of this oscillator is the reference diodes Q91 to Q9n.
To generate a forward drop voltage VD. Differential amplifier A
MP is the forward drop voltage VD of the reference diode and the resistor R3.
Amplifies the difference voltage between the terminal voltages of, and increases the current flowing through the resistor R3 through the transistors Q12 and Q13 so that the difference becomes zero. This current is fed back to the reference diodes Q91 to Q9n via the current mirror stage of the bias current generating circuit 20 and the current mirror stage of the oscillator 10, and finally reaches equilibrium.

This control loop is a positive feedback loop,
Since the saturation nonlinearity of the voltage with respect to the currents of the diodes Q91 to Q9n is large, the positive feedback ratio is small, and there is no fear of becoming unstable as a control loop.

In the steady state of the circuit of FIG. 1, the forward drop voltage of the clamp diodes D1 and D2 of the oscillator 10 is Vd,
Assuming that the currents of the transistors Q5 and Q6 are I1 and the value of the timing capacitor C is C, the oscillation frequency fo is 1
Will be indicated by.

On the other hand, the current I2 generated by the bias current generating circuit 20 is the forward voltage drop of the reference diode, which is V
If D and the resistance value of the resistor R3 are R, then I2 = VD / R. If the proportional coefficient in the control loop that makes I2 equal to the constant current value I1 of the oscillator 10 is K,

[0019]

(Equation 3)

## EQU1 ## Therefore, from equations 1 and 2, the oscillation frequency fo is

[0021]

(Equation 4)

## EQU1 ## Even if the current density of the clamp diode of the oscillator 10 and the current density of the reference diode of the bias current generation circuit 20 are made equal, Vd ≠ VD, and the temperature coefficient of the diode is several hundred ppm in absolute value in the switching operation rather than the DC operation. It was found that a large amount occurred at about / ° C.

Next, a method for compensating for the temperature coefficient of several hundred ppm / ° C. will be described with reference to FIG. Here, several hundred ppm / ° C. is treated as 500 ppm / ° C. for the sake of explanation. FIG. 2 is a graph showing the relationship between the current density and the temperature coefficient of a general diode. When the value of the constant current I1 is set to 45 μA in the oscillator, the current density of the clamp diode D1 (when the transistor Q1 is off and Q2 is on for a half cycle) is 9
The value is 0 μA / area (when the current flowing through the pull-up resistor R1 connected in parallel is regarded as almost 0). In the remaining half cycle, the current density of the clamp diode D2 is 90 μA.
/ Area. Considering the temperature coefficient of the oscillation frequency generated by the operating current of this current density as the temperature coefficient of the diode,
From Fig.2, it becomes -3000ppm / ° C, but this value is the value when the clamp diode is in DC operation, and in the switching operation, the temperature compensation component of -500ppm / ° C was added to -35ppm.
00ppm / ° C will be generated. On the other hand, the current density of the reference diodes Q91 to Q9n required to generate the temperature coefficient of -3500 ppm / ° C is 45 μA /
Area. The sum of the currents flowing into the reference diode is 3
・ I1 = 135μA, so reference diodes Q91-Q
The area (number) of 9n is 135 μA / 45 μA / area = 3
Becomes Therefore, by setting the area (number) of the clamp diodes to 1 and the area (number) of the reference diodes to 3, the temperature coefficient of the clamp diode and the temperature coefficient of the reference diode can be made equal, and Can be protected from temperature effects. The area ratio (number ratio) between the clamp diode and the reference diode
Is maintained at 1: n, the number of clamp diodes is not limited to one, for example. When the number of clamp diodes is one, the number of diodes can be minimized as a temperature compensation method including the reference diode.

FIG. 3 shows another embodiment of the present invention. The difference between the embodiment of FIG. 3 and the embodiment of FIG. 1 is that the bias current generating circuit 20 does not generate the current value to be given to the transistors Q5 and Q6 in the positive feedback loop configuration, but it is connected between the oscillator 10 and the power supply ground in series. A plurality of reference diodes Q91 to Q9n, which are connected in parallel, are provided by a circuit configuration of only connection.
A resistor R3 for setting a current proportional to the oscillation frequency based on the forward drop voltage of the reference diodes Q91 to Q9n,
Transistor Q for supplying this current to constant current circuits Q5 and Q6 of oscillator 10 and transistors Q17 and Q18
19 and the bias resistor R8. Further, in order to make the currents of the constant current circuits Q5 and Q6 of the oscillator 10 variable and to adjust the control current for setting the oscillation frequency,
Providing transistors Q17 and Q18 to provide transistor Q5
And Q6 to form a differential pair, and the control voltage Vc is applied to these base electrodes as the control input terminals 4 and 5.

The number n of reference diodes Q91 to Q9n required for temperature compensation in the circuit of FIG. 3 is obtained as follows. The control voltage Vc applied to the control input terminals 4 and 5 is 0
Considering the equilibrium state of, transistors Q5, Q6, Q1
Since a current I1 flows through each of 7 and Q18, the bias current generating circuit 20 generates a current four times as large as the operating current I1. Here, assuming that the operating current I1 is 45 μA and the current density of the clamp diode is 90 μA / area, the current density of the reference diodes Q91 to Q9n necessary for temperature compensation is 45 μA / area from FIG. Therefore, the reference diodes Q91 to Q9n have 4
Since it is necessary to generate a current of I1 = 180 μA, the number n required for the reference diodes Q91 to Q9n is 18
0 μA / 45 μA / area = 4. In this case, the current flowing through the reference diodes Q91 to Q9n is set by the resistor R8 and the power supply Vcc. As a result, it is possible to prevent the oscillation frequency from being affected by temperature, as in FIG.

Further, also in temperature compensation type variable frequency oscillators other than those shown in the figure, this temperature compensation method can be applied as long as the temperature coefficient of the clamp diode is compensated by using the temperature coefficient of the reference diode.

[0027]

According to the present invention, the temperature coefficient of the reference diode can be increased by setting the current density of the reference diode lower than the current density of the clamp diode. A sufficiently stable temperature-compensated variable oscillator can be realized with sufficient compensation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a current density of a diode and a temperature coefficient.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

[Explanation of symbols]

1, 4, 5 ... Control input terminal, 2, 3 ... Output terminal, Vcc
... power supply terminal, 10 ... oscillator, 20 ... bias current generating circuit, 30 ... clamp diode section, 40 ... reference diode section, R1 to R8 ... resistance, C ... timing capacitor,
Q1 to Q19 ... Transistors, Q91 to Q9n ... Reference diodes, D1, D2 ... Clamp diodes, CC1,
CC2 ... Constant current source, AMP ... Differential amplifier.

Claims (1)

[Claims] 1. A temperature-compensated variable frequency oscillator comprising a transistor pair of positive feedback connections, a clamp diode, a timing capacitor, an emitter-coupled multivibrator having a constant current circuit, and a bias current generation circuit having a reference diode. A temperature-compensated variable frequency oscillator, wherein the current density of the reference diode is set lower than the current density of the clamp diode.