JPH0480564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a voltage controlled multivibrator used in phased locked loops, FM modulators, and the like.

BACKGROUND ART Conventionally, multivibrator type oscillators have been often used as FM modulators in semiconductor integrated circuits.

FIG. 2 shows an example of a conventional voltage controlled multivibrator, and FIG. 3 shows the waveforms a to f in FIG. 2 (for example, Japanese Patent Publication No. 57-37248). Transistors 1, 2 and 8, 9 constitute a differential switching circuit, and switch the collector current I ₀ of transistor 41 and the current path of current source 10. Resistors 5 and 6 are connected to the collectors of transistors 1 and 2, respectively, and a capacitive element 7 is connected between the emitters of transistors 3 and 4. Transistors 11, 12, 13, and 14 constitute a comparison circuit, which compares the reference potential given by resistors 20, 21 and transistor 17, that is, the emitter potential of transistor 17 and the potential across capacitive element 7. There is. The current values of the current sources 15 and 16 are equal, and the current value of the current source 43 is also appropriate. 26
is a flip-flop circuit composed of transistors and the like. Terminals 22 and 23 are input terminals from the comparison circuit, and terminals 24 and 25 are output terminals having opposite phases.

The operation of the conventional example configured as above will be explained below.

The flip-flop circuit 26 includes a transistor 1
When the collector current of transistor 1 falls below a certain level, the output terminal 24 becomes a low level and the output terminal 25 becomes a high level, and the output state is maintained until the collector current of transistor 14 falls below a certain level. When the collector current of the transistor 14 falls below a certain level, the output terminal 24 becomes a high level and the output terminal 25 becomes a low level, and the output state is maintained until the collector current of the transistor 11 falls below a certain level.

At the output voltage of terminals 24 and 25, transistor 1
and 8 and transistors 2 and 9 perform a switching operation.

When the collector current of transistor 41 is _I0 , the voltage drop between the base and emitter of transistor 3 or 4 _{is VBE1} , and when the current of current source 43 is _I1 , the voltage drop between the base and emitter of transistor 17 is VBE1. _BE2 , assuming that the base potential of transistor 17 is V _B17 , when balanced with the reference voltage V _ref , V _E3
−ΔV=V _ref i.e. (+B) −V _BE1 −ΔV=V _B17 −
V _BE2 holds true and formula (1) is derived.

Here, V _E3 refers to the emitter potential of transistor 3 when it is conductive.

ΔV=+B−V _B17 −V _BE1 +V _BE2 (1) When V _BE1 =V _BE2 in equation (1), ΔV is equal to the voltage drop due to the resistor 20 and is a constant value. Since the amplitude of the waveform at both ends of the capacitance is 2ΔV as shown in Figure 3 c and d,
The oscillation frequency is expressed by equation (2).

=I ₀ /4C ₀ ΔV (2) Here, C ₀ is the capacitance value of the capacitive element 7.

Problems to be Solved by the Invention However, since the current value I ₁ of the current source 43 is fixed, if the collector current I ₀ of the transistor 41 changes, the value of V _BE1 changes (see Figure 4). In equation 1), the term -V _BE1 +V _BE2 is not constant, and the value of ΔV changes depending on the value of _I0 .
Also, transistor 3 (or 4) and transistor 1
If the emitter current of 7 is different, the temperature change rate of the base-emitter voltage drop V _BE will be different, so
The temperature characteristics of V _BE1 and V _BE2 do not match, and the temperature characteristics of ΔV in equation (1) differ depending on the value of I ₀ . That is, the circuit shown in FIG. 2 has the disadvantage that as I ₀ becomes larger, the difference in temperature change between V _BE1 and V _BE2 becomes larger, and the temperature dependence of the oscillation frequency becomes larger.

The present invention improves the drawbacks of conventional circuits and provides a voltage-controlled multivibrator that obtains an oscillation output with a stable frequency against temperature changes, regardless of the magnitude of the input.

Means for Solving the Problems To achieve this object, the voltage controlled multivibrator of the present invention provides a first transistor having one end connected to a common power supply to the collectors of the first and second transistors which are differentially coupled. and a second resistor, respectively, the base of the third transistor is connected to the collector of the first transistor, the base of the fourth transistor is connected to the collector of the second transistor, and the third and fourth transistors are connected to each other. a reference voltage generating circuit having a fifth transistor in its output stage whose base is supplied with a voltage and whose emitter outputs a reference voltage; a variable current source circuit that changes the current flowing from the conducting transistor through the capacitive element and the current flowing to the fifth transistor linearly with respect to the input voltage or input current; A comparator circuit that compares the emitter voltage of transistor No. 4 with a reference voltage, and an output state of the comparator circuit is inverted, and the first and second transistors are made conductive by the inverted signal.
It consists of a flip-flop circuit that reverses the non-conducting state.

Effect: With this configuration, the variable current source circuit causes the same current _I0 to flow through the fifth transistor of the output stage of the reference voltage generation circuit as the current flowing through the conductive one of the third and fourth transistors. By doing so, the value of V _BE and the temperature change with respect to the current _I0 can be made the same, the reference voltage can be changed in accordance with the change in V _BE , and the current that flows when the third and fourth transistors are conductive can be made the same. Fluctuations in the emitter potential due to the magnitude of VBE and changes in the emitter potential due to temperature fluctuations in _VBE can be canceled out, and an oscillation output with a stable frequency can be obtained.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the voltage controlled multivibrator of the present invention.

In FIG. 1, 1 and 2 are differentially coupled first
and the second transistors 5 and 6 are the first and second transistors.
This resistor constitutes a differential switching circuit together with transistors 8 and 9, and is a variable current source circuit 2.
₇ and the current path of the current source 10 are switched. 3 and 4 are third and fourth transistors whose emitters are coupled through a capacitor 7. Transistors 11, 12, 13, 14 and current sources 15, 16 are comparators, and the third,
The emitter potentials of the fourth transistors 3 and 4 are compared with the reference voltage, and the output is from the flip-flop circuit 2.
It is input to terminals 22 and 23 of 6.

The variable current source circuit 27 includes a voltage-current conversion circuit, transistors 28, 29, 30, and a resistor 3.
It is composed of a current mirror circuit of 1 and 32.

The reference voltage generation circuit includes transistors 17 and 18.
and resistors 19, 20, and 21, and the base of the transistor 18 is connected to the variable current source circuit 27.
is connected to the bases of transistors 28 and 29.

The operation of the voltage controlled multivibrator configured as above will be described below.

The description of the same operations as in the conventional example will be omitted, and the features of this embodiment will be described.

The voltage V ₀ applied to the input terminal 33 of the variable current source circuit 27 is first linearly converted into a current I ₀ by the voltage-current conversion circuit, and this current I ₀ flows through the transistor 28 . Transistors 28, 29, 30
The resistors 31 and 32 constitute a current mirror circuit, and the same current I ₀ as that of the transistor 28 flows through the transistor 29 . Therefore, current I ₀ is caused to flow through whichever of transistors 8 and 9 is conductive.

The reference voltage V _ref is the potential given by the resistors 20 and 21 and the transistor 17, that is, the potential given by the transistor 1
The emitter potential V _E17 of transistor 17 is V _ref = V _E17 = (+B) R ₂₁ / R ₂₀ + R ₂₁ − V _BE2 ...(3) (V _BE2 is the voltage drop between the base and emitter of transistor 17). It will be done.

Transistor 17 in the output stage of the reference voltage generation circuit
The current I ₁ flowing through is supplied from a current source composed of a transistor 18 and a resistor 19. By connecting the base of transistor 18 to the bases of transistors 28 and 29 of variable current source circuit 27, this current source is connected to transistors 28, 29,
30 and resistors 31 and 32 constitute a current mirror circuit.

Therefore, if the value of the resistor 19 is selected, the same current I ₀ as that of the transistor 29 flows through this current source, so that I ₁ =I ₀ . Therefore, the same current as that of transistor 3 or 4, whichever is conducting, can flow through transistor 17, and the voltage drops V _BE1 and V _BE2 between their respective bases and emitters are always the same. Can be a value.

In general, V _BE is expressed as: V _BE =kT/q)*ln(I _E /I _S ) K: Boltzmann's constant T: Absolute temperature I _S : Saturation current; V _BE has the same value if the emitter current I _E is the same, and the change in value due to temperature is also the same.

Emitter potential V _E3 when transistor 3 is conductive
is, V _E3 = (+B) - V _BE1 ...(4) (V _BE1 is the voltage drop between the base and emitter of transistor 3) When balancing with the reference voltage, V _E3 - ΔV =
V _ref, that is, from equations (3) and (4), (+B) − V _BE1 − ΔV = (+B) R ₂₁ /R ₂₀ +R ₂₁ − V _BE2 holds, and ΔV is ΔV=V _E3 −V _ref = (+B -V _BE1 ) -V _E17 = (+B - V _BE1 ) - (V _B17 - V _BE2 ) = (+B) R ₂₀ /R ₂₀ + R ₂₁ - (V _BE1 - V _BE2 )...(5). Here, since the same current I ₀ is passed through transistors 3 and 17 by the current mirror circuit of the variable current source circuit, the change in V _BE also changes in the same way, and V _BE1 = V _BE2 ...(6) This is always true, and formula (5) becomes ΔV=R ₂₀ /R ₂₀ +R ₂₁ ×(+B)...(7). ΔV is expressed as the voltage across R ₂₀ (the difference between the power supply voltage and the base voltage). In equation (7), the temperature characteristics of resistors R ₂₀ and R ₂₁ are relatively canceled, so there is no temperature dependence of ΔV.

Therefore, ΔV is the magnitude of input current I ₀ and V _BE1 ,
Since it can be expressed by an expression that does not depend on V _BE2 ,
If a capacitive element 7 is selected whose capacitance value changes little with temperature, as can be seen from equation (3), linearity with respect to the oscillation frequency input is good and fluctuations in the oscillation frequency due to temperature changes are small.

As described above, according to this embodiment, the same current is always passed through the transistors 3 or 4 and the transistor 17 to match the V _BE characteristics of each, and the reference voltage of the comparator circuit, that is, the emitter potential of the transistor 17, the emitter potential of the transistor 3 or 4, The structure is such that the emitter potential always changes in the same way when conducting. That is, in a current source composed of a transistor 18 and a resistor 19, the base of the transistor 18 is connected to the bases of transistors 28 and 29 of the variable current source circuit 27, and the transistors 28, 29, 30 and the resistor 3 are connected to each other.
By forming a current mirror circuit with 1 and 32, the voltage input to the variable current source circuit
The same current value I ₀ as the current I ₀ converted from V ₀ is passed through the transistor 17 of the output stage of the reference generation circuit, and V _BE2 is always maintained.
V _BE1 is set to the same value.

As a result, V _BE2 changes according to the magnitude of I ₀ , and the reference voltage V _ref changes by the change in V _BE2 , so even if V _BE1 changes according to the magnitude of I ₀ or the temperature changes. Regardless of the magnitude of the input voltage, a constant ΔV is always obtained regardless of temperature changes, and an oscillation output with an extremely stable frequency against temperature fluctuations is obtained, and the linearity of input voltage vs. oscillation frequency is also improved. .

Effects of the Invention As described above, the present invention provides a reference voltage generation circuit that supplies the current flowing to the fifth transistor of the output stage from the variable current source circuit and changes the reference voltage of the comparator circuit. Since the reference voltage can be changed according to fluctuations in the emitter potential of the conductive transistor and the fourth transistor, a stable oscillation output that is independent of temperature fluctuations can be obtained. This makes it possible to realize an excellent voltage-controlled multivibrator with good linearity of input voltage versus oscillation frequency, regardless of its size.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a voltage controlled multivibrator according to an embodiment of the present invention, Fig. 2 is a circuit diagram of a conventional example, and Fig. 3 is a main part a to f of the circuit shown in Fig. 2.
FIG. 4 is a diagram showing the relationship between the collector current of the transistor, V _BE and temperature. 1, 2, 3, 4...transistor, 5, 6...
Resistor, 7... Capacitive element, 8, 9... Transistor, 10... Current source, 11, 12, 13, 14...
...Transistor, 15,16...Current source, 17,1
8...Transistor, 19,20,21...Resistor, 22,23...Flip-flop input terminal,
24, 25...Flip-flop output terminal, 26
...Flip-flop circuit, 27...Variable current source circuit, 28, 29, 30...Transistor, 3
1, 32...Resistor, 33...Input terminal.

Claims (1)

[Claims] 1. First and second resistors each having one end connected to a common power supply are connected to the collectors of the first and second transistors that are differentially coupled, and the base of the third transistor is connected to the collectors of the first and second transistors that are differentially coupled. connected to the collector of the first transistor, and the base of the fourth transistor connected to the collector of the second transistor;
a circuit comprising a capacitive element coupled between the emitters of the third and fourth transistors; and a reference voltage generating circuit having a fifth transistor in its output stage, the base of which is supplied with a voltage and the emitter of which outputs a reference voltage; A current flowing through the capacitive element from one of the third and fourth transistors that is conducting is varied linearly with respect to the input voltage or input current, and the current flowing through the capacitive element is changed linearly with respect to the input voltage or input current. a variable current source circuit that causes a current having the same value as the current flowing through the fifth transistor to flow through the fifth transistor; a comparison circuit that compares the emitter voltages of the third and fourth transistors with the emitter voltage of the fifth transistor; A voltage-controlled multivibrator comprising: a flip-flop circuit that inverts an output state based on an output signal of the comparison circuit, and inverts conduction and non-conduction states of the first and second transistors based on the inversion signal.