JPS5910819Y2 - oscillation circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an oscillation circuit consisting of a differential amplifier, a time constant circuit, and a switching circuit, and is particularly designed to prevent problems caused by parasitic transistors when implemented as an IC.

FIG. 1 shows an example of an oscillation circuit to which the present invention can be applied.

In FIG. 1, 1a is a power supply terminal to which a first power supply voltage 1 is supplied, and 1b is a power supply terminal to which a second power supply voltage V2 is supplied.

Here, the power supply voltage V1 is higher than the power supply voltage V2 by at least the base-emitter voltage VBE of the transistor, and the power supply voltage V2 is formed from the power supply voltage V0 by a Zener diode or the like, and its value is stable. It is considered a thing.

Reference numeral 2 denotes a multi-collector type PNP transistor having collectors 3a and 3b, which, unlike other NPN transistors, is formed into an IC having a lateral structure on a P-type silicon substrate.

The emitter of this transistor 2 is connected to a power supply terminal 1a, and its collector 3a is connected to the base of a multi-emitter type transistor 4 having emitters 5a and 5b.

The collector of this transistor 4 is connected to the power supply terminal 1b, and its emitter 5a is led out as an output terminal 6 and is grounded via a series circuit of resistors 7 and 8.

A resistor 9 is inserted between the connection point of the resistors 7 and 8 and the power supply terminal 1b, and the base of one transistor 12 of the differential amplifier 10 is connected to this connection point.

A constant current source consisting of a transistor 13 is connected to the common emitter connection point of the transistors 11 and 12 of the differential amplifier 10, and a constant current source consisting of a transistor 14 having a common base with the transistor 13 is connected to the collector 3a of the transistor 2. and is connected to the connection point of the base of transistor 4.

A time constant circuit 17 in which a resistor 15 and a capacitor 16 shown surrounded by broken lines are connected in parallel is connected to the base of the transistor 11.

The time constant circuit 17 is externally attached to the IC.

This time constant circuit is connected to the emitter 5b of the transistor 4 via a resistor 18.

Furthermore, the collector of transistor 11 is connected to power supply terminal 1b, and the collector of transistor 12 is connected to power supply terminal 1a through a diode junction formed by commonly connecting the base and collector 3b of transistor 2.

The oscillation circuit of the above structure performs an oscillation operation by changing the base potential of the transistor 11 connected to the time constant circuit 17 as shown in FIG.

First, let us start with a period T2 in which the charge in the capacitor 16 is discharged through the resistor 15. During this period T2, the transistor 11 of the differential amplifier 10 is on, the transistor 12 is off, and the transistors 2 and 4 are also off. ing.

When the capacitor 16 is discharged and the base voltage of the transistor 11 becomes lower than the reference voltage obtained by dividing the power supply voltage 2 by the resistors 8 and 9, the transistor 11 of the differential amplifier 10 is turned off and the other transistor 12 is turned off. Turn on.

This turns on transistor 2, and transistor 2
The collector 3a of , that is, the base of the transistor 4 is (VBE
+V2), and therefore transistor 4
is turned on, and the voltage generated at its emitters 5a and 5b becomes approximately equal to (2).

The capacitor 16 of the time constant circuit 17 is therefore charged through the transistor 4 and the relatively small resistor 18.

Since the transistor 4 is on, the reference voltage applied to the base of the transistor 12 during this period T1 is
2, and as the base potential of the transistor 11 becomes higher than this raised reference voltage, the transistor 11 is turned on again, and a period T2 occurs in which the transistor 12 is turned off.

The relaxation oscillation operation is repeated as described above.

The reason why the power supply voltages V1 and 2 are used in such an oscillation circuit is that the transistor 4 is sufficiently turned on by the transistor 2 to make the emitter potential of the transistor 4 equal to V2, thereby reducing the voltage drop between the base and emitter of the transistor 4, VBH. This is to remove any fluctuations such as temperature fluctuations from the circuit.

However, when the transistor 4 is made into an IC, as shown by the broken line in FIG. A forward bias is applied to the emitter junction, and current flows into the silicon substrate through this parasitic transistor 4.

For this reason, the silicon substrate, which is generally at ground potential, comes to have a certain potential, and there are adverse effects such as leakage of oscillation output to other circuits formed on the same substrate.

The present invention is designed to avoid the adverse effects caused by such parasitic transistors.

Hereinafter, one embodiment of the present invention will be described with reference to FIG.

Similar to the oscillation circuit shown in FIG. 1 described above, the first power supply voltage ■,
the first power supply terminal 1a to which is supplied the power supply voltage v1;
A second power supply terminal 1b supplied with a lower second power supply voltage 2, a differential amplifier 10, and transistors 13 and 1
A constant current source consisting of 4 and a time constant circuit 17 are provided.

Also provided is a transistor 19 for adjusting voltage and temperature compensation, the base of which is connected to the power supply terminal 1b, and the collector of which is connected to the power supply terminal 1a.
A first resistor 20, a second resistor 21, and a third resistor 22 are inserted in series between the emitter and ground.

The connection point between the resistors 20 and 21 is connected to the emitter 5a of the multimeter transistor 4, and is also led out as an output terminal 6, the collector of which is connected to the power supply terminal 1a.

The base of this transistor 4 and the collector 3a of the multi-collector type transistor 2 are connected.

The emitter of this transistor 2 is connected to the power supply terminal 1b.

In addition, the transistor 4 can be considered as a first transistor having an emitter 5a and a fifth transistor having a common base and collector with the first transistor, including when it is not a multi-chip transistor, and similarly, the transistor 2 can be considered as a fifth transistor having a common base and collector. can be considered as a diode junction formed by commonly connecting the base and collector of a second transistor having a collector 3a and a third transistor whose base and emitter are common to the second transistor, even when it is not a multi-collector type. can.

That is, as shown in FIG. 5, the first transistor 4 and the fifth transistor 4' are configured as separate elements,
The second transistor 2 and the diode-connected transistor 2' may be constructed as separate elements.

According to the present invention, when the transistor 11 of the differential amplifier 10 is on and the transistor 12 is off (that is, during period T2), the reference voltage applied to the base of the transistor 12 varies from the power supply voltage 2 to the voltage of the transistor 19. Voltage drop between base and emitter ■The voltage after subtracting BE from the resistor 20
, 21 and 22.

Further, during the period T1 in which the on/off states of the transistors 11 and 12 are reversed, the transistors 2 and 4 are turned on.

At this time, the potential of the emitter 5a of the transistor 4 becomes a voltage obtained by subtracting the base-emitter voltage drop (BE) from the power supply voltage (2), and the reference voltage supplied to the base of the transistor 12 substantially increases.

Therefore, it performs the same oscillation operation as the oscillation circuit shown in FIG.

And the voltage drop between the base and emitter of transistor 4■
Variations in BE, such as temperature variations, are compensated by similar variations in the base-emitter voltage drop vBE of transistor 19.

As described above, according to the present invention, when transistor 4 is driven by transistor 2, it is possible to prevent forward bias from being applied to the base-emitter junction of parasitic transistor 4' by transistor 4, so that this parasitic transistor It is possible to avoid problems such as current flowing into the silicon substrate through 4, causing the substrate to be at a certain potential, or causing leakage of oscillation signals.

Therefore, there is no need to take parasitic transistors into consideration when implementing an IC, and there is an advantage that IC implementation becomes easy.

[Brief explanation of the drawing]

Figure 1 is a connection diagram of an example of the oscillation circuit proposed earlier.
Fig. 2 is a waveform diagram used to explain it, Fig. 3 is a diagram used to explain the parasitic transistor, Fig. 4 is a connection diagram of one embodiment of the present invention, and Fig. 5 is a connection diagram of another embodiment of the invention. It is a diagram. 1a is a first power supply terminal, 1b is a second power supply terminal, 10 is a differential amplifier, 17 is a time constant circuit, 20, 21. 22
are the first, second, and third resistances.

Claims (1)

[Scope of utility model registration request] A first power supply terminal to which a first power supply voltage is supplied, a second power supply terminal to which a second power supply voltage lower than the first power supply voltage is supplied, and a series connection between the second power supply terminal and a reference potential point. a first transistor, the emitter of which is connected to the connection point of the first and second resistors, and the collector of which is connected to the first power supply terminal; and a second transistor whose base and collector of the first transistor are connected and whose emitter is connected to a second power supply terminal, and a connection point between the base of the first transistor and the collector of the second transistor. It includes a constant current source connected to it, a differential amplifier made up of third and fourth transistors, and a time constant circuit connected to the base of the third transistor, and the collector of the third transistor is connected to the second transistor.
At the same time, its base is connected to the emitter of a fifth transistor whose base and collector are common to the first transistor through a resistor, and the base of the fourth transistor is connected to the emitter of the fifth transistor whose base and collector are common to the first transistor. An oscillation circuit in which the collector of the fourth transistor is connected to the connection point of the resistor and the base and emitter of the fourth transistor are connected to the second power supply terminal via a common diode junction.