JPH0222703Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a voltage comparator that operates stably over a wide voltage range.

Generally, when performing a delayed sweep on an oscilloscope,
The start point of the horizontal sweep signal is delayed from the start point of the horizontal sweep signal when performing a normal sweep, and a voltage comparator is used to obtain a signal that determines the start point of the horizontal sweep signal for delayed sweep.

FIG. 1 is a circuit diagram showing an example of a conventionally used voltage comparator. In the figure, a diode 3 for protecting the first transistor 1 and a second transistor 2 is connected to the emitters of the transistors.
The anodes of the diode 3 and the diode 4 are connected to each other, and the cathodes of the diode 3 and the diode 4 are both connected to a negative power supply -V via a resistor 5 that functions as a constant current source. The base of the transistor 1 is connected to the input terminal 6, and the collector is connected to the cathode of the tunnel diode 7 and the output terminal 8. Further, the collector of the transistor 2 is connected to the anode of the tunnel diode 7 and the positive power supply +V, and the base is supplied with a reference voltage obtained by dividing the positive power supply by a variable resistor 9.

The operation of the conventional circuit configured as described above is as follows. When no signal is supplied to input terminal 1, transistor 2 is conductive because the reference voltage set by variable resistor 9 is supplied to its base, but transistor 1 is conductive when no input signal is supplied. Because there is no current, there is no conduction. Here, when a sawtooth signal is supplied to input terminal 1, the base voltage of transistor 1 increases with time,
When the base voltage of transistor 1 approaches the base voltage of transistor 2, current begins to flow through transistor 1. When the base voltage of transistor 1 further increases, the current in transistor 1 rapidly increases, and the emitter voltage increases, so that transistor 2 becomes non-conductive.

The current change of the transistor 1 is converted by the tunnel diode 7 into a square wave signal with a sharp rise, and is supplied to the output terminal 8.

However, the emitter voltage of transistor 1 at this time changes as shown in FIG. In the figure, Vin is the sawtooth signal supplied to the input terminal 6, V _R is the reference voltage set by the variable resistor 9, +V is the positive power supply voltage, and V _E in the bold line is the base-emitter voltage. This is the emitter voltage when transistor 1 is turned on when not in use.

Since the collector voltage of transistor 1 is approximately +V of the positive power supply, the difference between +V and V _E in FIG. 2 represents the emitter-collector voltage of transistor 1. Therefore, the area of the shaded part in Figure 2 represents the power consumption of transistor 1, that is, the amount of heat generated, and as is clear from Figure 2, the area of the hatched part
The lower the _VR , the more heat generated. Therefore,
Adjusting the comparison voltage to adjust the delay time causes a change in heat generation, which causes the voltage between the base and emitter of the transistor to fluctuate, and this voltage has the disadvantage that it does not stabilize until the temperature of the transistor reaches an equilibrium state. was.

Therefore, an object of the present invention is to provide a voltage comparator that operates stably against large changes in reference voltage.

In order to achieve such an object, the circuit according to the present invention has a field effect transistor inserted in series with the collector of each differentially connected transistor. The present invention will be explained in detail below using the drawings.

FIG. 3 is a circuit diagram showing an embodiment of the voltage comparator according to the present invention, and the same symbols are used for the same parts as in FIG. 1. In the figure, 10 and 11 are N-channel field effect transistors, and the drains of the field effect transistors 10 and 11 are connected between the collector of transistor 1 and the tunnel diode 7 and between the collector of transistor 2 and the power supply. and source connected.
The gate of field effect transistor 10 is connected to the base of transistor 1, and the gate of field effect transistor 11 is connected to the base of transistor 2. In addition, field effect transistor 1
0 and the zero bias drain current I _Dss of the field effect transistor 11 is selected to be larger than the collector current flowing through the transistor 1 and the transistor 2.

The operation of the voltage comparator according to the present invention configured as above is as follows. When a sawtooth signal is supplied to the input terminal 6, when the base voltage of the transistor 1 becomes greater than the base voltage of the transistor 2, the transistor 1 suddenly becomes conductive and generates an output signal at the output terminal 8. In this case, the zero bias drain current of the field effect transistor 10
Since I _Dss is selected to be larger than the collector current Ic flowing through the transistor 1, the characteristics of the field effect transistor 10 are as shown in FIG. In Figure 4, the vertical axis is the drain current Ib,
The horizontal axis is shown as the gate-source voltage V _Gs . Then, a current of the same magnitude as the collector current Ic flowing through the transistor 1 flows through the field effect transistor 10, and the voltage between the gate and source of the field effect transistor 10 to allow this current Ic to flow is V _Gs1 from Fig. 4. . This voltage V _Gs1 is generally 1
Since it is a low value of about ~2 volts, the emitter-collector voltage of transistor 1 when conductive is the sum of the above V _Gs1 of 1 to 2 volts and the base-emitter voltage of transistor 1 of about 0.7 volts. . Since the transistor 1 is connected to a constant current source, the collector current is constant and the emitter-collector voltage of the transistor 1 is also constant.

Therefore, the emitter voltage V _E of transistor 1
The collector voltage Vc changes as shown in FIG. 5, and the shaded area represents the amount of heat generated by the transistor 1. Therefore, compared to a conventional voltage comparator where the area surrounded by the power supply voltage +V and the emitter voltage _VE of transistor 1 is the amount of heat generated, as shown by the shaded area in FIG. , the voltage comparator according to the present invention generates extremely little heat. As a result, even if the set voltage of the variable resistor 9 is changed to adjust the delay time, the amount of heat generated changes only slightly, and the base-emitter voltage of the transistor 1 does not change. Therefore, it can operate stably over a wide voltage range.

Regarding the conductivity type of field effect transistors, when transistor 1 and transistor 2 are NPN type, N channel is used, but when they are PNP type, P channel is used.
You can use it as a channel.

As explained above, the voltage comparator according to the present invention has a field effect transistor connected in series to the collector circuit of the transistor constituting the differential amplifier, and the base of the transistor and the gate of the field effect transistor are connected in common. Because of this, the heat generated by the transistor is extremely small, and has the excellent effect of allowing stable voltage comparisons to be made over a wide voltage range.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventionally used voltage comparator, Fig. 2 is a graph showing changes in emitter voltage of transistor 1 in the circuit of Fig. 1, and Fig. 3 is a voltage according to the present invention. A circuit diagram showing one embodiment of the comparator, FIG. 4 is a graph showing characteristics of a field effect transistor, and FIG. 5 is a graph showing changes in emitter and collector voltages of transistor 1 in the circuit of FIG. 3. 1, 2...transistor, 6...input terminal, 8
...Output terminal, 9...Variable resistor, 10, 11...
field effect transistor.

Claims (1)

[Scope of utility model registration request] In a voltage comparator constituted by a differential amplifier consisting of a first transistor and a second transistor, a source and a drain are connected in series to the collector circuit of the first transistor, and a gate is connected to the base of the first transistor. and a second field effect transistor having a source and a drain connected in series to the collector circuit of the second transistor and a gate connected to the base of the second transistor. A voltage comparator characterized in that: