JPH01147908A - Differential amplifier - Google Patents

Abstract

PURPOSE:To prevent a transistor(TR) of a differential circuit from being saturated even when an input voltage is equal to a negative power supply by inserting a Shottky diode in a feedback loop of a current mirror circuit receiving a differential circuit. CONSTITUTION:When a signal at an input terminal 11a is higher than a signal at a terminal 11b (at H level), a TR 1a is turned off, a TR 1b is turned on, a TR 3b is turned off and TRs 5b, 7 are turned on and the signal at an output terminal 12 goes to L. Conversely, when the signal at the input terminal 11a is at L, the signal at the output terminal 12 goes to H. When the signal at the input terminal 11a is equal to the voltage of a negative power supply 14, the emitter voltage of the TR 1a is Vbe. The collector voltage of the TR 2a is expressed as 2Vbe(TRs 2a, 5a)-VF4a(Schottky diode 4a)-Vbe(TR3a)=VbeVF4a. Then the emitter-collector voltage Vce of the TR 1a is expressed as Vce= Vbe-(Vbe-VF4a)=VF4a, and since it is not zero, the TR 1a is not saturated and no malfunction takes place.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a differential amplifier, and particularly relates to an improvement in input dynamic range. [Prior Art] Fig. 2 shows a conventional differential amplifier. It is a circuit diagram.

In the figure, 1allb is a PNP transistor constituting a differential circuit whose emitters are commonly connected; its emitter is connected to the constant current source 8, and its base is the differential input terminal 1)! ,
1) bK connected. Further, the collector is connected to a current mirror constituted by NPN transistors 2a and 2b, the collector of PNP transistor 13 is connected to the collector and base of NPN transistor 23, and the collector of PNP transistor 1b is connected to the collector of NPN transistor 2b. As well as NPN
Connected to the base of transistor 3.

Further, the collector of the transistor 3 is connected to the constant current source 9 and to the base of the NPN transistor 5. The NPN transistor 5 is.

Its collector is connected to the positive power supply 13, and its emitter is NP
N Connected to the base of the transistor 7 and also connected to the league cut resistor 10. Above NPN
The transistor 7 is an output transistor, and the collector of the transistor 7 is connected to the load resistor 15 and the output terminal 12, and the emitter is connected to the negative power supply 14.

Further, the curved end of the resistor 15 is connected to the positive fl source 13.

Next, the operation when this differential amplifier is used as a comparator will be explained.

Now, let us consider a case where a reference voltage is applied to the input terminal 1) and a signal at the input terminal 1) bK'H' (a signal with a higher potential than the reference voltage) is applied thereto.

At this time, the PNP transistor 1λ in the differential circuit is on and the transistor elb is off, and the current supplied by the constant current source 8 flows from the emitter of the PNP transistor 1a to the collector, forming a current mirror. It becomes an electric current. Therefore, NPN) transistor 2b tries to flow a current equal to this current, but
Since the NPN transistor 1b is off, the NPN transistor 2b is saturated. That is, the transistor 2
No current flows through the collector of b. Further, the Ni'N transistor 3 is turned off because the base current is not supplied, and the current supplied by the constant current source 9 becomes the base current of the NPN transistor 5. Therefore, NPN transistors 5 and 7 are turned on, and output terminal 12 outputs 1L'.

Similarly, if input terminal 1) bKゝL' signal (a signal with a lower potential than the reference voltage) is input manually, PNP transistor 1 turns off & 1b turns on, and NPN transistor 2a turns off.
is off, and 2b is on. Therefore, the NPN transistor 3 is turned on because it is supplied with the base current from the PNP transistor 1b, and draws in all the current supplied by the constant current source 9.

Therefore, NPN transistors 5 and 7 are turned off.

The output terminal outputs 1H'.

[Problem that the invention seeks to solve]

Since the conventional differential amplifier is configured as follows,
When an input voltage close to the negative power supply is applied to the input terminal, the PNP transistor forming the differential circuit becomes saturated.

That is, input terminal 1). With a as the reference voltage, input terminal 1
) 1% when the same voltage as the negative power supply 14 is applied to b
'If the voltage between the base and emitter of the transistor is Vbe, then PNi') The emitter and peak voltages of transistor 1b are:
[Negative power supply voltage (0) + 1'' Vb6 (transistor 1b)], and the collector voltage becomes (negative power supply voltage (o) + 1·Vbe (transistor 3)),
Emitter-collector voltage VC of PNP transistor lb
e becomes approximately 0, and the PNP transistor lb is saturated (I current does not flow). Therefore, it becomes impossible to supply base current to the NPN transistor 3, and when the input signal is %L (negative power supply voltage) #2, the output should be 'H', but %1. I have had the problem of becoming I.

This invention was made to solve the above-mentioned problems, and aims to provide a differential amplifier that does not malfunction even when the input signal is at a negative power supply voltage and has a small offset voltage. shall be.

[Means for solving problems]

In the differential amplifier according to the present invention, a current mirror receiving a differential circuit is constructed of a PNP transistor, an NPN transistor, and a Schottky diode.

[For production]

In this invention, in a current mirror.

A Schottky diode is inserted into the feedback loop composed of a PNP transistor and an NPN transistor, and this makes it possible to raise the collector potential of the NPN transistor, which serves as a reference, from the base potential by F, and also increases the voltage between collector and base. The voltage VCE can be kept constant. Therefore, even if the two-power signal drops to the negative power supply voltage, the PNP transistor forming the differential circuit does not saturate, and the output circuit outputs the signal.

[Embodiments of the invention]

Hereinafter, embodiments of the invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a circuit array in which a differential amplifier according to an embodiment of the present invention is applied to a comparator.

In the figure, 3a and 3b are PNP transistors.

5 ” * 5 b * 7 is NPN) transistor @ 4
a + 4b is a Schottky diode 1) 01) 1
0b is a resistor, ga, gb are constant current sources, and the second
Portions equivalent to those of the conventional example shown above are indicated by the same reference numerals.

Input terminals 1)1.1)b are connected to the bases of PNP transistors 1a+1b, respectively.

A differential circuit is constituted by the transistors 1 a and 1 bK. In addition, the collectors of the PNP transistors 1a and 1b are NPN transistors constituting a current mirror, respectively.
A PNP transistor 3a is connected to the collector of the transistor 2a12b and serves as an emitter follower.
*3 It is vc after common to the base of b. The cathodes of Schottky diodes 4a14b are connected to the emitters of the transistors 3a@3b, respectively.

Further, constant current sources 9a and 91Ji are connected to the anode sides of the Schottky diodes 4a*4b, respectively, and one Schottky diode 41 is connected to an NPN transistor 2a constituting the current mirror.
The base of an NPN transistor f15a for supplying a base current of t2b is connected, and the base of an NPN transistor 5b constituting the output circuit is connected to the anode side of the second Schottky diode 4b.

The collector of the NPN transistor 5a is connected to the positive power supply 13, and the emitter of the NPN transistor 5a is connected to the NPN transistors 2a and 2b forming a current mirror.
are commonly connected to the bases of the current mirrors, and also connected to a resistor tOa for preventing oscillation in the feedback system of the current mirror t. Further, the bent end of the resistor 10a is connected to the negative power source 14. The collector of the NPN transistor 5b constituting the output circuit is connected to the positive power supply 13', and the emitter of the NPN transistor 5b forms an emitter follower and is connected to the base of the output transistor 7, as well as to the leakage cut resistor 10b. Ru.

In addition, a load resistor 15 is connected to the collector of the output Nl'N transistor, and this point is connected to the output terminal 12 &
I: Connect.

Next, the operation will be explained.

Consider a case where a reference voltage is applied to input terminal 1)b, an input signal is input to input terminal 1)a, and this differential amplifier circuit is used as a comparator.

Now, if the input signal is 1H' (reference voltage edge height m),
PNP transistor 1a forming a differential circuit is off, 1b
is turned on. Therefore, N constitutes a current mirror.
The collector current of PN transistor 2a is %PNP)
Basel flow of transistor 3a, that is, constant current source 9a
This means that the current is 1/hfe. Here, the currents flowing from the constant current sources 819a and 19b are respectively 18, 19a, and 1.
9b, 1 t81 ) I (9a) = 1(sb
) holds true, the collector current of the NPN transistor 2a, which is the output of the current mirror, is 19a/
It becomes hfe.

Therefore, the PNP) transistor 3b is no longer able to pass the base current and is turned off, and the current 19b supplied from the constant current source 9b becomes the base current of the NPN transistor 5b, and the NPN) transistor 5b is turned on.
As a result, the output transistor 7 is also turned on, and the output terminal 12
outputs a 'L' signal.

Consider the case where the input signal of input terminal 1)a is %LM (lower than the reference voltage). PNP forming a differential circuit
Transistor 1a is on and transistor 1b is off.

The bias current I8 supplied by the constant rti current source 8 is P
N constitutes a current mirror from the NP transistor 1a.
l'N) Collector of transistor 2a becomes [fi.

Current mirror output side N P N transistor 2b
Since the collector of tries to flow a current equal to the bias current 18, the l'NP transistor 3b turns on,
All of the current a I 9 b supplied from the constant current source 9b becomes a current at the emitter 4 of the PNP transistor 3b.

Therefore, the NPN transistor 5b constituting the output circuit
, 7 are turned off, and the output terminal 12 outputs a 1HI signal.

Now, for the case where a voltage equal to the negative power supply 14 is applied to the input terminal 1) a, the PNP that forms a differential (b) path
Emitter-collector voltage VCela of transistor 1a
think of.

The emitter voltage of PNP transistor 1a is 1・Vbe
(Negative power supply voltage (0) + base-emitter voltage of transistor 1a (・Vbe)) Also, the collector voltage is NP
Since it is equal to the collector voltage vc2a of the N transistor 2a, this voltage is determined.

vc2a = Vbe2a” Vbe5a −Vbe3
a -VF4aHowever, -Vbe' Base-emitter voltage of each transistor VF4a'' Forward voltage of Schottky diode 4a Therefore, Vce1a=Vbe-(2Vbe-Vbe VF4a
)=VF4a Tonal. Also, the collector-emitter voltage VC of the NPN transistor 2a! 21 becomes vCe2a = Vbe - VF4a. Here, the forward voltage of the Schottky diode is generally about 0.25 (V) when the forward current is 10 (μA).
). Therefore, the collector-emitter voltage of each transistor is a fixed value, so even if a human input signal equal to the negative power supply voltage is input to the input terminal, the comparator will not malfunction.

It is possible to obtain a signal at the output terminal, and the input dynamic range is wider than that of conventional circuits.

Further, in this embodiment, since the two-circuit type is configured symmetrically around the differential circuit, it is possible to reduce the offset voltage.

In addition, in the above embodiment, the case where the differential amplifier of the present invention is used as a comparator has been explained.
By providing a phase compensation capacitor between 2 and the collector of the PNP transistor 1b forming a differential circuit, and applying feedback between the output terminal 12 and the input terminal 1)a, it may be used as an operational amplifier. It has a similar effect.

In addition, in the above embodiment, the reference voltage is applied to llb and the input terminal is set to lla, or the reference voltage is applied to input terminal 1)H and the signal input terminal is set to iib.
However, the same effect as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the collector voltage of the NPN transistor constituting the current mirror is made lower than the base voltage, and when a voltage equal to the negative power supply is applied to the input terminal, a differential circuit is formed. Since the PNP transistor is prevented from saturating, it has the effect of providing a wide input dynamic range and a small offset voltage.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a differential amplifier according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional differential amplifier. 1a+1b+3a*3b is PNP transistor, 2
a+ 2 b* 5 a + 5 b 17 is an NPN transistor @ 4 ” + 4 b is a Schottky diode, 8°9a, 9b are constant current sources, 10a, 10b,
15 is a resistor, 1)1.1)b is an input terminal, 12 is an output terminal, 13 is a positive power supply, and 14 is a negative power supply. Note that the intermediate symbol A indicates the same or equivalent part. Agent Masu Oiwa Usui Figure 1 10k, 10bJ5: Kame f9 Figure 2

Claims (1)

[Claims] (1) In a differential amplifier composed of a differential input circuit and an output circuit that are directly connected to input terminals, the differential input terminal of the differential input circuit is connected to the bases of the first and second differential transistors. and the first and second differential transistors are
The emitters of the third and fourth transistors are commonly connected, and the collectors of the third and fourth transistors are connected to a first constant current source that sets a bias current, and the collectors of the third and fourth transistors form a current mirror, and the fifth and fourth transistors form emitter followers. The collectors of the fifth and sixth transistors are connected to the negative power supply, and the emitters of the fifth and sixth transistors are connected to the cathodes of the first and second Schottky diodes, respectively. The anode side of the first Schottky diode is connected to a second constant current source and to the base of a seventh transistor for supplying base current to the third and fourth transistors. The transistor 7 has its collector connected to the positive power supply, its emitter connected to the third and fourth bases, the anode side of the second Schottky diode connected to the third constant current source, and the emitter follower connected to the third constant current source. The collector of the eighth transistor is connected to the positive power supply, the emitter of the eighth transistor is connected to the base of the ninth output transistor, and the collector of the ninth output transistor is connected to the load. A differential amplifier characterized in that it is connected to a positive power supply via a resistor and is also connected to an output terminal.