JPH0476529B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a voltage controlled oscillator having an emitter-coupled unstable multivibrator configuration used in an integrated circuit FM modulator or the like.

[Technical background of the invention]

FM modulates video and audio signals
As a modulator, there is a voltage controlled oscillator as shown in FIG. The oscillation unit 100 is supplied with the modulated signal Vin via the signal supply circuit 200 and output to the output unit 10.
1, an FM modulated signal can be obtained. 3
00 is a bias circuit that supplies a bias voltage to the bias terminal 16 of the oscillation section 100.

The operation of the oscillation section 100 will be explained. The oscillation unit 100 is composed of transistors 1 to 7, 10, and 11, resistors 8 and 9, a capacitor 12, and current sources 13 and 14, with transistor 1 being turned on (hereinafter referred to as ON).
), and when transistor 2 is off (hereinafter referred to as OFF), the current I _O
flows, and in the opposite state, a current I _O flows as shown by the broken line in the figure.

Hereinafter, with reference to the signal waveforms shown in FIG. 4, temporal changes in the collector potentials V _C1 and V _C2 and the emitter potentials V _E1 and V _E2 of the transistors 1 and 2 will be explained.
In the oscillation operation, transistors 1 and 2 are turned on alternately,
This can be obtained by repeating the inversion of OFF, but first assume a state where transistor 1 is turned on and transistor 2 is turned off at time _t1 .

At this time, since the transistor 3 is also turned on, the collector potential V _C1 of the transistor 1 becomes a voltage lower than the potential of the bias voltage 16 by the base-emitter voltage V _BE3 of the transistor 3. Since the potential of the bias voltage 16 is V _CC −V _O , the collector potential of the transistor 1 at time t ₁ is V _C1
is V _C1 = V _CC −V _O −V _BE3 (t=t ₁ ). In addition, since transistor 2 is turned off, the collector potential V _C2 of transistor 2 is lower than the power supply voltage V _CC by the base-emitter voltage V _BE5 of transistor 5, and V _C2 = V _CC −V _BE5 (t=t ₁ ).

Next, consider the emitter potentials V _E1 and V _E2 of transistors 1 and 2 at time t ₁ . Here, the voltage between the base and emitter of transistor 7 is V _BE7 , and the voltage between the base and emitter of transistor 1 in the ON state is V BE7.
If V _BE1 , then V _E1 =V _CC -V _BE5 -V _BE7 -V _BE1 (t= _t1 ).

At this time, a current I _O flows through the capacitor 12 as shown by the solid arrow in FIG. As a result, the capacitor 12 is charged at a constant rate with the polarity in the direction of the solid arrow, and as a result, the emitter potential V _E2 of the transistor 2 is charged at a constant rate after time _t1 , as shown in FIG. 4D. and decreases. Then, the emitter potential V _E2 continues to decrease,
When the base-emitter voltage V _BE2 of transistor 2 reaches a certain value, the state of transistor 2 is OFF.
Switch from to ON. If the value of the emitter voltage V _BE2 that causes this inversion is V _BE2(ON) , and the time of inversion is t ₂ , then the emitter potential V _E2 of transistor 2 at time t ₂ is V _E2 = V _B2 − V _{BE2( ON)} (t=t ₁ ). Here, V _B2 is the base potential of transistor 2, and V _B2 is the collector potential of transistor 1.
Since the base-emitter voltage V _BE6 of transistor 6 is lower than V _C1 , it is expressed as V _B2 = V _C1 −V _BE6 = V _CC −V _O −V _BE3 −V _BE6 , and as a result, V _E2 = V _CC −V _O −V _BE3 −V _BE6 −V _BE2 (ON) (t=t ₂ ) is calculated.

When transistor 2 is reversed from OFF to ON,
Transistor 1 is inverted from ON to OFF. Therefore, this time the collector potential of transistor 1
V _C1 becomes V _C1 = V _CC −V _BE5 (t=t ₂ ), and the collector potential V _C2 of transistor 2 becomes V _C2 = V _CC −V _O −V _BE4 (t=t ₂ ). Then, the emitter potential V _E2 of transistor ₂ turned ON at time t 2 is similar to the emitter potential V _E1 of transistor 1 at time t ₁ , V _E2 = V _CC −V _BE5 −V _BE6 −V _BE2 (t = t ₂ ). Here, V _BE2 is the transistor 2 in the ON state.
represents the base-emitter voltage of

Now, at time _t2 , the emitter potential V _E2 of transistor 2 increases from V _CC −V _O −V _BE3 −V _BE6 −V _BE2 (ON) to V _CC −V _BE5 −V _BE6 −V _BE2 , minus V _O +V _BE3 −V _BE5 +V _BE2(ON) −V _BE2 is increasing. Here, when transistor 3 is in the ON state, resistor 8 is selected so that the current flowing through the collectors of transistor 3 and transistor 5 is equal, and the base-emitter voltage V _BE3 of transistor 3 and the base of transistor 5 are equal.・The emitter voltage V _BE5 is equal. Therefore,
The increase in the emitter voltage V _E2 of transistor ₂ at the previous time t 2 V _O +V _BE3 −V _BE5 +V _BE2(ON) −V _BE2 is, since V _BE3 = V _BE5 , V _O +V _BE2(ON) − V _BE2 . From this, the emitter voltage V _E1 of transistor 1 at time t ₂ becomes a potential higher than V _CC −V _BE5 −V _BE7 −V _BE1 at time t ₂ by the above increase, and V _E1 = V _CC −V _BE5. It can be seen that -V _BE7 -V _BE1 +V _O +V _BE2 (ON) - V _BE2 (t= _t2 ).

After time _t2 , when transistor 1 is OFF and transistor 2 is ON, current I _O flows in the direction of the dashed arrow in _FIG . As shown in C, it decreases at a constant speed. Then, transistor 1 turns from OFF to ON, so the necessary base
If the emitter-to-emitter voltage is V _{BE1 (ON)} , then at the time when V _E1 = V _CC −V _O −V _BE4 −V _BE7 −V _BE1 (ON) (time t ₃ ), transistor 1 is turned on again.
turns on and transistor 2 turns off.
Emitter voltage of transistor 1 in ON state
V _E1 returns to V _E1 = V _CC −V _BE5 −V _BE7 −V _BE1 (t=t ₃ ), and the increase in V _E1 at time t ₃ is V _O +V _BE4 −V _BE5 +V _BE1 (ON )−V _BE1 . As before, the value of resistor 9 is selected so that the base-emitter voltages V _BE4 and V _BE5 of transistors 4 and 5 are both equal, so in the end, the increase in V _E1 at time t ₃ becomes V _O +V _BE1(ON) −V _BE1 . From this, the emitter voltage V _E2 of transistor 2 at time t ₃ is higher than V _CC −V _BE5 −V _BE6 −V _BE2 before time t ₃ by the above increase, V _E2 = V _CC −V _BE5 −V _BE6 −V _BE2 +V _O +V _BE1 (ON) −V _BE1 (t=t ₃ ).

After that, transistors 1 and 2 are repeatedly turned ON and OFF, and the collector potential of transistor 1 increases.
V _C1 or collector potential of transistor 2 V _C2
As shown in FIGS. 4A and 4B, respectively, these are pulse waveforms that are repeated at a constant period of 2T, and an oscillation output is obtained from the output section 101. In this case, due to the change in collector potential V _C1 of transistor 1 during period T, the terminal voltage of capacitor 12 changes from V _CC −V _O −V _BE4 −V _BE7 −V _BE1(ON) to V _CC −V during period T. _BE5 −V _BE7 −V _BE1 +V _O +V _BE2 (ON) −V _BE2 , changing by 2V _O +V _BE1 (ON) −V _BE1 +V _BE2 (ON) +V _BE2 . By choosing transistors 1 and 2 symmetrically, V _BE1 = V _BE2 and V _BE1 (ON) = V _BE2 (ON), so the change in the voltage applied to capacitor 12 is 2 (V _O + V _BE1(ON ). ₎ +V _BE1 ). Therefore, the capacitance of the capacitor 12 is C
Then, C・2(V _O +V _BE1(ON) −V _BE1 )=I _O・T holds true, so the oscillation frequency f _O is f _O =1/2T=I _O /4CV _C …… (1) is obtained. Here, V _C is the voltage of transistors 1 and 2.
The terminal voltage of the capacitor 12 when ON and OFF are reversed, and is expressed as V _C =V _O +V _BE2(ON) −V _BE1 (2).

An input signal to the oscillation section 100 is supplied to the bases of transistors 10 and 11.

In the signal supply circuit 200, an input signal _Vio is supplied to the emitter of a transistor 23 via a resistor 21. Power supply voltage V _CC is supplied to the emitter of transistor 23 via resistor 22 . The collector of the transistor 23 is grounded via a diode-connected transistor 28, and the base of this transistor 28 is connected to the transistors 10 and 11.
connected to the base of. Further, a series circuit consisting of a resistor 26, diode-connected transistors 25 and 24, and a resistor 27 is connected between the power supply and the ground, and the base of the transistor 24 is connected to the transistor 2.
It is connected to the base of 3 and supplies bias.

Here, the emitter voltage V _E23 of the transistor 23
is, V _E23 = V _CC −V _E26 −V _BE25 /R ₂₆ +R ₂₇・R ₂₇ +V _BE23Here , V _E23 = V _BE26 = V _BE27 = V _J , R ₂₆ = R ₂₇ , then V _BE23 = V It becomes _CC /2. Therefore, the collector current I _C23 of the transistor 23 is I _C23 =V _io −V _BE23 /R ₂₁ +V _CC −V _BE23 /R ₂₂ =V _io −V _CC /2/R ₂₁ +V _CC /2/R ₂₂ , I _O = I _C10 = I _C11 = I _C28 = I _C23 due to the current mirror effect, I _O = V _io −V _CC /2/R ₂₁ +V _CC /2/R ₂₂ (3). Therefore, f _O = 1/4CV _C・(V _io −V _CC /2/R ₂₁ +V _CC /2/R ₂₂
) ...(4).

From equation (4), it can be seen that the oscillation frequency f _O changes by changing the input voltage, that is, V _io . Therefore, for example, in a video tape recorder, the input signal can be a video signal or an audio signal, and the above circuit can be used as an FM modulator.

[Problems with background technology]

The oscillation frequency f _O of the voltage controlled oscillator described above is dependent on the power supply, and there is a problem in that the center frequency varies due to fluctuations in the power supply voltage.

This point will be explained in detail below. A bias from a bias circuit 300 is applied to the bias terminal 16 of the oscillation section 100 . The bias circuit 300 has a configuration in which resistors 31 and 33 and a diode-connected transistor array 34 are connected in series between a power supply and ground, and a bias is taken out from the connection between the resistors 31 and 33.

The potential difference V _O between the output terminal voltage of the bias circuit 300 and the power supply voltage V _CC is expressed as V _O =V _CC -n·V _J /R ₃₁ +R ₃₃ ·R ₃₁ (5). From equations (2) and (5), V _C = V _CC −n・V _J /R ₃₁ +R ₃₃・R ₃₁ +V _BE2(ON) −V _BE1 ……(6). Here, the n diode-connected transistor array 34 is used to cancel the temperature drift of V _{BE2 (ON)} - V _BE1 .

In other words, in order to cancel the temperature drift, ∂/∂T(−n・V _J /R ₃₁ +R ₃₃ )+∂/∂T(V _BE2(ON) −
V _BE1 )=0 ...(7) where the temperature coefficient of V _J is negative and V _BE(ON)
Since the temperature coefficient of −V _BE1 is also negative, equation (7) can be satisfied by appropriately selecting n.

However, since these transistors are in the bias circuit, the oscillation frequency is dependent on the power supply.
In other words, from equations (1), (2), (3), and (5), the oscillation frequency f _O
is, F _O = 1/4C・V _io −V _CC /2/R ₂₁ +V _CC /2/R ₂₂ /V _CC −
nV _J /R ₃₁ +R ₃₃・R ₃₁ +V _BE2(ON) −V _BE1 . Here, let us find the value of the oscillation frequency _fO when there is no signal, that is, the value of the center frequency _fOO . The value of the modulated signal V _io when there is no signal is V _CC /2,
At this time, from equation (3) above, the current I _O is the power supply voltage V _CC
I _O = V _CC /2)/R ₂₂ , and V _BE2(ON) ,
V _BE1 can ignore the power supply voltage characteristics, and V _BE2(ON) V _BE1
Considering this, f _OO = 1/4C V _CC /2・1/R ₂₂ /V _CC・R ₃₁ /R ₃₁ +R ₃₃ −
nV _J /R ₃₁ +R ₃₃・R ₃₁ = 1/8C・1/R ₂₂ −1/R ₂₁ /R ₃₁ /R ₃₁ +R ₃₃ −nV _J /
V _CC・R ₃₁ /R ₃₁ +R ₃₃ ...(8) This leaves a term for V _CC , and therefore,
It can be seen that f _OO has power supply voltage dependence.

Therefore, when a conventional voltage controlled oscillator is used as an FM modulator for video and audio signals of a video tape recorder, the center frequency shifts due to variations in the power supply voltage, making it impossible to obtain the desired characteristics. .

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a voltage controlled oscillator whose oscillation frequency does not depend on the power supply voltage.

[Summary of the invention]

For example, as shown in _FIGS . 1 and 2, the present invention is capable of generating a voltage difference between the base potentials of the third and fourth transistors and the base potential of the fifth transistor of the oscillation section 100 by changing the power supply voltage V CC . so as to offset the amount by which the emitter voltage of the transistor changes due to the change in the current value of the voltage controlled current source controlled by the first voltage source 200 which changes in proportion to the power supply voltage, a second voltage source 300 that determines base potentials of the third and fourth transistors;
is configured so that it changes in proportion to the power supply voltage.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows one embodiment of the present invention, and the basic configuration is the same as that of the voltage controlled oscillator shown in FIG. However, in this invention, the oscillation section 10
Since the structure of the transistor 5 and the internal connection of the bias circuit 300 are different from each other, the structure of this part will mainly be explained.

In the bias circuit 300, resistors 31 and 33 are connected in series between a power supply and ground, and a connection portion between the resistors 31 and 33 is connected to the bias terminal 16. As a result, the bias voltage V _O between the bias terminals 16 becomes proportional to the power supply voltage V _CC . Further, in the oscillation section 100, when the transistor 1 is ON and the transistor 2 is OFF, a current I _O flows as shown by the solid line. That is, a current from the emitter of the transistor 3 and a current flowing from the emitter of the transistor 5 via the resistor 8 flow into the collector of the transistor 1 . Conversely, when transistor 1 is OFF and transistor 2 is ON,
Current I _O flows as shown by the broken line. At this time, a current from the emitter of the transistor 4 and a current flowing from the emitter of the transistor 5 via the resistor 9 flow into the collector of the transistor 2 .
Note that the above-mentioned current I _O is given by the above-mentioned equation (3). That is, it is proportional to the power supply voltage V _CC when there is no signal. Here, the emitter area of transistor 5 is configured to be m times the emitter area of transistors 3 and 4. Since the other parts are the same as those shown in FIG. 3, they are numbered the same as those shown in FIG. 3, and their explanation will be omitted.

Next, the operation of the above embodiment will be explained. Bias voltage between power supply voltage V _CC and bias terminal 16
V _O is expressed as V _O =R ₃₁ /R ₃₁ +R ₃₃ ×V _CC . Considering the point at which transistor 1 changes from ON to OFF, in the circuit of FIG. 3, V _BE3 = V _BE5 because the emitter areas and currents of transistors 3 and 5 are equal, but in the circuit of this example, , transistor 5 is provided, and its emitter area is m times the emitter area of transistor 3, so V _BE3 ≠ V _BE5 . Considering this, the terminal voltage V _C of capacitor 12 is V _C = V _O +V _BE3 −V _BE5 +V _BE2(ON) −V _BE1Here , V _E3 = V _E5 , V _E2 = I _2(ON) , V _E1 = I _O ,
(V _2(ON) ≪I _O ), then V _C =V _O +V+lnI _E3 /I _S −V _T lnI _E5 /mI _S +V _T lnI _2(ON)
/I _S −V _T lnI _O /I _S =V _O +V _T ln (m・I _O /I _2(ON) ) Where, I _S : Saturation current V _T : kT/q k: Boltzmann constant q: Unit Charge T: Absolute temperature. Here, the normal value of V _T ln (m・I _O /I _{2 (ON)} ) is small compared to V _O , so V _C is almost equal to V _O , and V _C V _O = R ₃₁ / R ₃₁ + R ₃₃・V _CC , which can compensate for the temperature drift of V _C , and also reduce V _C
will be proportional to V _CC . Therefore, when there is no signal
The oscillation frequency when V _io = V _CC /2 is f _OO = 1/4C・V _CC /2 1/R ₂₂ /R ₃₁ /R ₃₁ +R ₃₃・V _C
It can be expressed as _C = ¹ / ₁ /8C・_R31 + _R33 / _R31・1/ _R22 . As can be seen by comparing this equation with equation (8), f _OO is independent of V _CC ;
Independent of power supply voltage.

If high matching accuracy between V _C and V _O is required, the emitter area ratio m of transistors 3 and 5 should be selected as m=I ₂ (ON)/I _O , and this will reduce the center frequency f _OO . This is ensured by its independence from the power supply voltage V _CC .

FIG. 2 shows another embodiment of the invention. In the case of this embodiment, the configuration of the bias supply circuit 300,
The means for applying bias to the bases of transistors 3, 4, and 5 of the oscillation section 100 is different from the previous embodiment.

Bias circuit 300 has resistors 32, 31, and 33 connected in series between a power supply and ground. resistance 3
The connection portion between resistors 31 and 33 is connected to the base of transistor 51, and the connection portion between resistors 31 and 33 is connected to the base of transistor 52. transistor 5
The emitter area of transistor 2 is m times the emitter area of transistor 51. The elector of the transistor 51 is connected to a power supply, and the emitter is connected to a constant current source 53.
grounded through. Further, the collector of the transistor 52 is connected to a power supply, and the emitter is grounded via a constant current source 54. The emitter of transistor 52 is connected to the base of transistor 5, and the emitter of transistor 51 is connected to the bases of transistors 3 and 4.

Next, the operation of this embodiment will be explained. The voltage V _O between the bases of the transistors 51 and 52 is
Even in the case of the configuration shown in the figure, V _O =R ₃₁ /R ₃₁ +R ₃₂ +R ₃₃ ×V _CC is expressed and is proportional to the power supply voltage. In this embodiment, since V _BE51 and V _BE52 are added to the path from V _O to the terminal voltage V _C of the capacitor 12, V _C
is V _C =V _O +V _BE51 +V _BE52 +V _BE2(ON) −V _BE1 . Here, I _E51 = I ₅₃ , I _E52 = I ₅₄ , I _E2 = I _2(ON)
,
If I _E1 = I _O , (I _2(ON) ≪I _O ), then V _C = V _O +V _T lnI ₅₃ /I _S −V _T lnI ₅₄ /I _S +V _T lnI _2(ON) /I _S
−V _T lnI _O /I _S =V _O +V _T ln (m·I _O /I _{2 (ON)} ).

The following is the same as in the previous embodiment: V _C V _O =R ₃₁ /R ₃₁ +R ₃₂ +R ₃₃ ·V _CC , and the temperature drift of V _C is compensated and is proportional to V _CC .

Therefore, the oscillation frequency f _OO when V _io = V _CC /2
is, f _OO = 1/4C V _CC /2・1/R ₂₂ /R ₃₁ /R ₃₁ +R ₃₂ +R ₃₃・
It can be expressed as V _CC =1/8C·R ₃₁ +R ₃₂ +R ₃₃ /R ₃₁ ·1/R ₂₂ .

From the above, f _OO becomes independent of V _CC and can be made independent of the power supply voltage. Also m=
By setting I _2(ON) /I _O , the accuracy of matching between V _O and V _C is increased, and the independence of the center frequency f _OO from the power supply voltage V _CC becomes more reliable.

〔Effect of the invention〕

As explained above, according to this invention, V _O and I _O
By changing the value in proportion to the power supply voltage, it is possible to provide a voltage controlled oscillator whose center frequency does not depend on the power supply voltage while also compensating for temperature drift without complicating the circuit.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, Fig. 2 is a circuit diagram showing another embodiment of the invention, and Fig. 3 is a circuit diagram showing another embodiment of the invention.
This figure is a circuit diagram of a conventional voltage controlled oscillator, and FIG. 4 is a signal waveform diagram shown to explain the operation of the circuit of FIG. 3. 1 to 7, 10, 11, 51, 52...transistor, 8, 9, 31 to 33...resistance, 12...capacitor.

Claims (1)

[Scope of Claims] 1 The first and second transistors have first and second transistors each having a capacitor connected between their emitters, and third, fourth, and fifth transistors having collectors connected to a power supply. emitters of the two transistors are each connected to a voltage controlled current source, the collector of the first transistor is connected to the base of the second transistor, and the collector of the second transistor is connected to the base of the first transistor. Each is connected via a feedback loop, and
The collectors of the first and second transistors are connected to the emitters of the fifth transistor via resistors, respectively, and the collectors of the first and second transistors are connected to the emitters of the third and fourth transistors, respectively. , the bases of the third and fourth transistors are commonly connected, and a bias circuit is connected with a potential difference between the common base and the base of the fifth transistor, the voltage controlled oscillator comprising: Due to the change, the current value flowing through the voltage controlled current source changes, and as a result, the third,
between the base potential of the third and fourth transistors and the base potential of the fifth transistor such that the voltage between the emitter potential of the fourth transistor and the emitter potential of the fifth transistor changes at a rate equal to the rate of change; A voltage controlled oscillator characterized in that the voltage of the oscillator is set to vary in proportion to the power supply voltage.