JPH053932B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current controlled oscillator, and particularly to a current controlled oscillator suitable for improving the temperature characteristics of oscillation frequency.

[Conventional technology]

Generally, the oscillation frequency _p of an emitter-coupled multivibrator type current controlled oscillator is expressed by the following equation.

_p = I _p /4CV _d ...(1) where I _p is the current, C is the timing capacitance, and V _d is the forward voltage drop of the clamp diode.

When equation (1) is partially differentiated with respect to temperature T, the temperature coefficient of _p becomes ∂ _p /∂T=1/V _d ∂V _d /∂T (2), and depends on the temperature coefficient of V _d . In order to remove this effect, I _p in equation (1) is linked to V _d and the resistance
A method such as setting with R _p is being considered. According to this, equation (1) can be transformed as follows.

_p = V _d /R _p /4CV _d = 1/4CR _p (3) Therefore, since V _d is eliminated, the temperature coefficient of the oscillation frequency can be made zero.

Related oscillators of this type include, for example, A.B. Greben, "Bipolar and Moth Analog Integrated Circuit Design" (1984), pp. 575-581;
John Willy & Sons (AB)
GREBENE, BIPOLAR AND MOS
ANALOG INTEGRATED CIRCUIT
DESIGN, (1984), p575-581, John Wiley
& Sons Inc.).

[Problem that the invention seeks to solve]

In the conventional example described above, a diode with the same current density as the clamp diode is connected below the multivibrator, and although consideration has been given to the temperature characteristics with respect to the oscillation frequency, a difference appears in the temperature coefficient. The cause of this is the current amplification factor of the switching element of the emitter-coupled multivibrator.
It is thought that the transconductance g _n due to the finite value of h _FE has an influence. The influence of this g _n generates a thermal voltage inside the switching element, resulting in a loss of forward voltage drop of the clamp diode. That is, equation (3) is expressed as follows.

_p = V _dL / 4CR _p (V _du − Ic / g _n ) …(4) However, V _dL = V _du , V _dL ; Forward drop voltage of the lower diode of the multivibrator, V _du , of the clamp diode Forward drop voltage.

For this reason, the amplitude appearing at both ends of the timing capacitor usually has a value smaller than ±V _d and has a positive temperature coefficient, so there has been a problem that a current-controlled oscillator with sufficiently high temperature stability cannot yet be obtained.

An object of the present invention is to provide a current controlled oscillator that can eliminate the influence of g _n and obtain a highly stable oscillation frequency that is not subject to temperature fluctuations, and to provide a current controlled oscillator that can be used over a wide range by changing the value of the reference resistor R _p . An object of the present invention is to provide a current controlled oscillator whose set frequency can be changed.

[Means for solving problems]

The above purpose is to convert the switching element g _n (=Ic/
Considering that the internal voltage of the switching element is generated by the product of the proportionality constant _m and the thermal voltage _V By dividing the voltage subtracted from the forward drop voltage V _d of the diode by the reference resistance R _p to set I _p for frequency setting, and by changing the value of the reference resistance R _p , the frequency can be set. This is achieved by varying the current _Ip .

[Effect]

V _T of the mV _T generation circuit is generated by a differential pair, and m is set by the ratio of the load resistance of the differential pair, that is, the current ratio. By subtracting the mV _T value obtained in this way from the forward drop voltage of the lower diode of the multivibrator using a differential amplifier, the temperature coefficients of the clamp diode and the diode can be canceled, resulting in high temperature stability. The oscillation frequency can be obtained, and the set value of the oscillation frequency can be easily changed by simply changing the reference resistance value.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, Q1 and Q2 are transistors, which are a pair of switching elements. A load consisting of a clamp diode D1 and a resistor R1, and an emitter follower consisting of a transistor Q3 and a constant current source CC1 are connected from the power supply terminal 5 to the collector of the transistor Q1. On the other hand, a clamp diode D is connected to the collector of transistor Q2.
2 and a load consisting of a resistor R2, and a transistor Q
An emitter follower 4 consisting of a constant current source CC2 is connected from a power supply terminal 5. In addition, constant current source CC
The same current value is supplied to CC1 and CC2.

The base of the transistor Q1 is the transistor Q
4 and the second output terminal 2.
On the other hand, the base of the transistor Q2 is connected to the emitter of the transistor Q3 and the first output terminal 1. Note that frequency output waveforms of opposite phases are obtained at the first and second output terminals 1 and 2.

The emitter of transistor Q1 is connected to one end of timing capacitor C and the collector of transistor Q5. On the other hand, the emitter of transistor Q5 is connected to the other end of timing capacitor C and transistor Q6.

Transistors Q5 and Q6 are transistor Q7
It constitutes a current mirror whose primary side is .
The above configuration represents an emitter-coupled multivibrator.

Next, the emitters of transistors Q5, Q6, and Q7 are connected to the anode of diode D3, and the cathode thereof is at ground potential.

Transistor Q8 is connected to input terminal 3 of mV _T generating circuit 10, and its output terminal 4 is connected to the positive phase input of operational amplifier 20. operational amplifier 20
The negative phase input of is connected to the transistor Q8 and one end of the resistor R _p , and its output is connected to the base of the transistor Q8. Furthermore, one end of the resistor R _p is at ground potential.

The collector of transistor Q8 is connected to the source of MOS transistor M1. MOS transistors M1 and M2 constitute a current mirror with M1 as the primary side. Furthermore, the source of MOS transistor M2 is connected to the collector of transistor Q7.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be explained. Now, in an emitter-coupled multivibrator, if we consider the state where transistor Q1 is off and transistor Q2 is on, transistor Q2
_The base _of
forward voltage drop of and transistors Q1, Q
2, Q3, Q4 base-emitter voltage)
Furthermore, the emitter becomes Vcc-2V _d . On the other hand, the base of the transistor Q1 is at Vcc- _2Vd . At this time, a sum of constant currents 2I _p (I _p is the collector current of transistors Q5 and Q6) flows through transistor Q2. This current flows into the transistor Q5 through the emitter current of the transistor Q2 and the I _p flowing into the transistor Q6, and the timing capacitor C.
Branched into I _p minutes. Therefore, the emitter of transistor Q1 falls with the slope of I _p /C (C is timing capacitance C), and when this emitter becomes less than Vcc-3V _d , the base is at Vcc-2V _d , so transistor Q1 is turned on. Then, transistor 12
Instead, a current of 2I _p begins to flow through transistor Q1, and the emitter of transistor Q1 becomes Vcc-
2V _d and turns off the transistor Q2. At this time, the emitter of transistor Q1 rose from Vcc-3V _d to Vcc-2V _d by V _d , so
This rise in V _d is also transmitted to transistor Q2 via timing capacitor C, causing its emitter to rise to Vcc.
-V _d . This operation constitutes a half cycle, and transistors Q1 and Q2 are turned on alternately to repeat oscillation.

The oscillation waveforms of each part of this operation are shown in FIG. In Figure 2, (a) is the waveform of the first output terminal 1, that is, the base of the transistor Q2, (b) is the waveform of the second output terminal 2, that is, the base of the transistor Q1, and (c) is the waveform of the base of the transistor Q1.
shows the waveform of the emitter of transistor Q2, (d) shows the waveform of the emitter of transistor Q1, and (e) shows the waveform of (c) to (d), that is, the waveforms at both ends of timing capacitor C.

Next, I _p for setting the oscillation frequency of the emitter-coupled multivibrator is generated by the mV _T generation circuit 10 from the forward drop voltage V _dL of the diode D3 connected to the bottom of this multivibrator.
Set the voltage by subtracting the voltage mV _T divided by the resistance R _p . This I _p is the MOS transistor M
1 and M2 into the transistor Q7. In this way, I _p can be set after adding the amount mV _T , so
Equation (4) is expressed as follows.

_p = 1/4CR _p (V _dL - mV _T )/(V _dU - mV _T ) = 1/4C
R _p ...(5) However, V _dU = V _dL , and the temperature coefficient of _p is ∂ _p /∂T=0...(6).

Therefore, it is possible to generate the amount mV _T and cancel the influence due to the g _n of the transistor Q1 or Q2, including the temperature coefficient. In addition, mV _T
The amount of cancellation can be obtained by varying m. Therefore, as shown in FIG. 3, the oscillation frequency becomes as shown in (b) with respect to temperature changes, and a current-controlled oscillator with high temperature stability can be realized. Note that (a) is the conventional temperature characteristic.

Further, a desired oscillation frequency can be obtained by changing the resistance R _p . This can also be seen from equation (5).

Also, instead of MOS transistors M1 and M2
PNP bipolar transistors can also be used.

Furthermore, by setting the current ratio of the current mirror made up of MOS transistors M1 and M2 and the current mirror made up of transistors Q7, Q5, and Q6 to 1:n, the current set by resistor R _p can be made smaller, resulting in lower power consumption. .

Furthermore, by connecting a resistor to the emitter of each of the transistors Q7, Q5, and Q6, variations in the current ratio of the current mirror can be reduced.

Next, a specific embodiment of the mV _T generating circuit 10 shown in FIG. 1 is shown in FIG. 4. In FIG. 4, 3 and 4 are denoted by the same reference numerals as in FIG. 1, and are the input and output terminals of the mV _T generating circuit 10, and 5 is a power supply terminal as in FIG. Input terminal 3 is connected to the base of transistor Q11. Transistor Q1
The collector of MOS transistor M12 is connected to the gate of MOS transistor M12 and one end of resistor R11. The emitter of transistor Q11 is connected to the emitter of transistor Q12 and one end of resistor RE. The collector of transistor Q12 is connected to the gate of MOS transistor M11 and one end of resistor R12. The base of transistor Q12 is connected to the emitter of transistor Q14, one end of resistor R15, and output terminal 4. The base of transistor Q14 is connected to the collector of transistor Q13 and resistor R.
It is connected to one end of 14. The base of transistor Q13 is connected to the cathode of diode D11 and the anode of diode D12. Diode D
Anode No. 11 is connected to one end of resistor R13. The other end of the resistor R13 is connected to the source of the MOS transistor M12. Resistor R14
The other end of is connected to the source of MOS transistor M11. The power supply terminal 5 is connected to the other end of the resistor R11, the other end of the resistor R12, the collector of the transistor Q14, the drain of the MOS transistor M11, and the MOS transistor M1.
Connected to the drain of 2. Further, the other end of the resistor RE, the other end of the resistor R15, the emitter of the transistor Q13, and the cathode of the diode D12 are at ground potential.

The operation of the embodiment shown in FIG. 4 is as follows:
MOS transistors M11 and M12, resistor R13, and diode D1 are connected so that this voltage difference becomes zero.
1, D12, transistors Q13, Q14, and a resistor 15. A differential amplifier that converts a differential signal into a single-ended signal forms a loop to control the base voltage of the transistor Q12. Now, assuming that the base-emitter voltages of transistors Q11 and Q12 are V _BE1 and V _BE2 , respectively, and the currents flowing through resistors R11 and R12 are I ₁ and I ₂ , respectively, the bases of transistors Q11 and Q12, that is, the input and output terminals 3, A differential voltage V _BE1 - V _BE2 is generated between the two. This differential voltage is expressed as follows.

V _BE1 −V _BE2 =V _T l _o I ₁ /A _E I _SO −V _T l _o I ₂ /A _E I _SO =V _T l _o
I ₁ /I ₂ = V _T・m...(7) However, A _E : Emitter area of the transistor I _SO : Collector reverse saturation current per unit area Therefore, V _T is obtained as the difference voltage between the two transistors. , m can be obtained as the natural logarithm of the current ratio I ₁ /I ₂ . In addition, the current
Regarding the setting of I ₁ /I ₂ , if the resistors R11 and R12 are R ₁ and R ₂ respectively, there is a relationship of I ₁ R ₁ = I ₂ R ₂ (condition for the collector voltages of transistors Q11 and Q12 to be equal). , set by resistance ratio. That is, I ₁ /I ₂ =R ₂ /R ₁ (8).

In this way, the voltage mV _T can be generated with any resistance ratio.

Further, the differential amplifier is not limited to the one shown in FIG. 4, and may be a commonly used differential amplifier.

Furthermore, PNP transistors can also be used in place of the MOS transistors M11 and M12.

〔Effect of the invention〕

According to the present invention, the temperature influence due to g _n of the switching element of an emitter-coupled multivibrator can be reduced.
By generating and canceling the voltage mV _T , a highly stable oscillation frequency can be obtained.

Further, in the current controlled oscillator, the oscillation frequency is obtained by setting the current value using a resistor, so by setting the resistance value to an arbitrary value, a wide range of oscillation frequencies can be stably obtained.

Furthermore, the current controlled oscillator configuration can operate with a low voltage power supply because the number of series stages is small.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the current controlled oscillator of the present invention, Fig. 2 is a diagram showing operating waveforms of the emitter-coupled multivibrator of Fig. 1, and Fig. 3 is a diagram showing the relationship between temperature and oscillation frequency. , Figure 4 is the same as Figure 1.
FIG. 2 is a diagram showing a specific example of an mV _T generation circuit. 1, 2...first and second oscillation frequency output terminals,
3, 4...mV _T generation circuit input and output terminals, 5...
...Power supply voltage terminal, C...Timing capacity, Q1~
8...Transistor, D1-3...Diode,
R1, 2, R _p ...Resistance, cc1,2 ... Constant current source,
M1, 2,...MOS transistor, 10...
mV _T generation circuit, 20...differential amplifier.

Claims (1)

[Claims] 1. An emitter-coupled multivibrator whose oscillation frequency can be set by a current, and a current density equal to that of a clamp diode of the multivibrator provided below the multivibrator for setting the oscillation frequency of the multivibrator. A current controlled oscillator comprising a diode and a frequency setting circuit that sets a current using a resistor based on the forward voltage of the diode, a generation circuit that generates a reference voltage consisting of a product of a proportionality constant and a thermal voltage is provided, A current controlled oscillator characterized in that the current is set based on a voltage obtained by subtracting the forward voltage of the output from the reference voltage generating circuit. 2. In claim 1, the reference voltage generation circuit uses a differential pair having a pair of load resistances to generate the reference voltage, and the differential output is transmitted to the differential pair via a differential amplifier. A current controlled oscillator characterized by having a configuration in which one input has negative feedback. 3. In claim 2, as a differential amplifier of the reference voltage generation circuit,
A current controlled oscillator characterized by having a circuit configuration capable of converting a differential signal into a single-ended signal. 4. In claim 2, the proportionality constant in the reference voltage generation circuit is:
A current controlled oscillator characterized in that the ratio of the load resistances of the differential pair, that is, the current ratio, is determined as a natural logarithm value.