JPH04129306A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To eliminate a DC offset by using a 3rd transistor(TR) and a 2nd constant voltage source so as to make a collector voltage of a 1st TR equal to a collector voltage of a 2nd TR. CONSTITUTION:A differential current based on an input voltage Vin of an input signal is fed to each base of emitter common TR differential pair comprising 1st and 2nd TRs Q3, Q4 in this amplifier circuit, a collector of the 1st TR Q3 connects to an emitter of the 3rd TR Q5 whose collector connects to a current mirror circuit CM and whose base connects to a constant voltage source 22, and a collector of a 2nd TR Q4 is connected to the current mirror circuit CM so as to arrange collector-emitter voltages VCE of the 1st TR Q3 and the 2nd TR Q4 thereby preventing adverse effect due to the Earley's effect and eliminating the DC offset.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplifier circuit suitable for use in, for example, an integrated circuit (IC).

(Summary of the Invention) The present invention allows differential current based on an input signal to be
The collector of the first transistor is connected to a transistor whose collector is connected to a current mirror circuit and whose base is connected to a constant voltage source. The present invention provides an amplifier circuit that can suppress DC offset by connecting the collector of a transistor to a current mirror circuit and taking out a current output from the collector.

[Conventional technology]

For example, a circuit as shown in FIG. 2 is known as an operational amplifier circuit used as an internal circuit of an integrated circuit (IC).

In FIG. 2, a differential signal from an input stage 51 whose input signal supplied to an input terminal 50 is a differential current is transmitted through a pair of NPN transistors constituting a common emitter transistor differential pair.
type transistors 53 and 54. A current mirror circuit consisting of a diode 55 and a PNP transistor 56 is connected to the collector of each of these transistors 53 and 54.
The collector of transistor 3 is connected to the cathode of diode 55, and the collector of transistor 54 is connected to the collector of transistor 56. The anode of the diode 55 and the emitter of the transistor 56 are supplied with the vce power, and the common emitter of the transistor 5354 is supplied with the constant current source 5.
It is grounded via 7. The output from the collector of transistor 54 is taken out via output terminal 60.

[Problem to be solved by the invention]

By the way, in the operational amplifier circuit as shown in FIG. 2, when the differential signal component from the input stage 51 is 0,
Both transistors 53 of the common emitter transistor differential pair
．． The currents flowing through 54 should be equal to each other. However, if the collector voltages of the transistors 53 and 54 are different, and a difference occurs in the collector-emitter voltage vcI+, the currents flowing through the transistors 53 and 54 will be different due to the so-called Early effect. At this time, a so-called DC offset appears in the output, which causes deterioration of distortion rate characteristics, etc., which is undesirable.

The present invention has been proposed in view of the above-mentioned circumstances, and an object of the present invention is to provide an amplifier circuit capable of amplification with suppressed DC offset.

[Means to solve the problem]

The amplifier circuit of the present invention was proposed to achieve the above-mentioned object, and the input signal is supplied as a differential current, and each other end is commonly connected and connected to a first constant voltage source. a common-emitter transistor differential pair consisting of first and second diodes, first and second transistors whose bases are respectively supplied with differential currents from the first and second diodes; a third transistor connected to the collector of the first transistor and connected to the base or a second constant voltage source; and a current mirror connected to the collector of the third transistor and the collector of the second transistor. The current output is taken out from the collector of the second transistor.

[Effect]

According to the present invention, the third transistor and the second constant voltage source control the collector voltage of the first transistor and the second
The collector voltages of the first and second transistors are made equal to each other. By making the collector-emitter voltages of the second transistors equal to each other, the adverse effect of the Early effect is prevented and the DC offset is eliminated.

〔Example〕

Embodiments to which the present invention is applied will be described below with reference to the drawings.

In the amplifier circuit according to the embodiment of the present invention shown in FIG. 1, an input signal (input current Vlfi) via an input terminal 1 is supplied as a differential current, and each other terminal is commonly connected to a first constant voltage source. NPN transistors Ql, Q2 operating as first and second diodes connected to 21 and these transistors Ql.

A common emitter transistor differential pair consisting of first and second NPN transistors Q3 and Q4, each of which has a differential current from Q2 supplied to its base, and a base whose emitter is connected to the collector of the first transistor Q3. has a third NPN transistor Q5 connected to the second constant voltage source 22, and a current mirror circuit CM connected to the collector of the third transistor Q5 and the collector of the second transistor Q4. , the current output 10 is taken out from the collector of the second transistor Q4 via the output terminal 2.

In FIG. 1, an input signal (input voltage V, . . . ) supplied to an input terminal l is supplied to the base of a PNP transistor QIO. The base of this transistor QIO is connected to a constant voltage source (for example, cc/2 power source) via a resistor R5. In addition, PNP type transistor Ql
The base of l is connected to a constant voltage source (e.g. V) via a resistor R6.

c/2 power supply). Furthermore, the bases of these transistors Q10 and Qll are connected via the resistors R5 and R6. These transistors QlO,Q
11 collectors are supplied with Vcc power through resistors R1 and R2, and each transistor Q
The collector outputs of IO and Qll are connected to transistors Q12.
Sent to the base of Q13.

These transistors Q12. The emitters of Q13 are connected to each other via a resistor RE, and the emitters are supplied with, for example, a current I from a current source 10.11. That is, as shown in equation (1), the input voltage V4.
is converted into a current 11++ by the resistor RE.

i, =V+*/RE...""" (1) The collectors of these transistors Q12 and Q13 are connected to the collectors of the transistors Q1 and Q2, respectively.Therefore, the collectors of the transistors Ql and Q2 are connected to each other. The input voltage V1. of the input signal is supplied as a current (differential current).

The collector and base of the transistor Ql are connected,
Since the collector and base of transistor Q2 are also connected, these transistors Ql.

Q2 operates as a diode. Of course, this transistor Q1. Q2 may be a normal diode. Also, the transistor Q1. The emitters of Q2 are commonly connected and grounded via the first constant voltage source 21. This causes transistor Q1. The base potential (collector output) of Q2 is the voltage V1 of the first constant voltage source 21 and the base potential of each of the transistors Ql and Q2.
Emitter voltage V. Which sum (V 1 + V BE) will be the potential. These transistors Q1. The collector output (differential current) from Q2 is the first one. Second transistor Q3. Sent to each base in Q4. That is, the voltage v1 of the first constant voltage source 21 causes the transistor Q
l, Q2. Q3. The base potential of Q4 is determined.

The emitters of the transistors Q3 and Q4 are commonly connected and grounded via a current source 12 having a current value I2, for example.

Further, the current mirror circuit CM includes a PNP type transistor Q6. Q7. Q8. This is a so-called Wilson type current mirror circuit consisting of Q9. That is, this Wilson type current mirror circuit CM has a transistor Q
6 and Q8 are commonly connected, and the common connection point is connected to the collector of transistor Q8, and the collector of transistor Q6 and the emitter of transistor Q7, and the collector of transistor Q8 and transistor Q
9 emitters are connected, and these transistors Q
The bases of transistor Q7 and Q9 are commonly connected, and the common connection point is also connected to the collector of transistor Q7. Transistor Q6 of this current mirror circuit CM. The Vcc power supply is supplied to the emitter of transistor Q8 through a resistor R3°R4, the collector output of transistor Q7 is connected to the collector of transistor Q3 through transistor Q5, which will be described later, and the collector output of transistor Q9 is connected to transistor Q4. sent to the collector. According to this Wilson type current mirror circuit CM, the transistor Q7
．． Almost uniform output currents can be obtained from Q9. An output current 10 is taken out from the collector of the transistor Q4 via an output terminal 2.

Output current 1 taken out from output terminal 2 of this example circuit
0 is usually further extracted as a voltage by, for example, an operational amplifier. In this case, for example, the output current 10
is supplied to the inverting input terminal of an operational amplifier 30 whose non-inverting input terminal is grounded via a constant voltage source 31 of voltage VE and which has a negative feedback loop resistance RL, so that the output of the operational amplifier 30 becomes the output voltage V It comes to be output from terminal 3 as D u I . That is, (2)
As shown in (2), = RL The voltage of the source 31 becomes VE.

Here, when the differential signal component of the input signal is 0, both transistors Q of the common emitter transistor differential pair are
3. The currents flowing through Q4 should be equal to each other.

However, these transistors Q3. The collector voltage of Q4 is different, and each collector-emitter voltage V. 8, the currents flowing through the transistors Q3 and Q4 will differ due to the so-called Early effect. At this time, a so-called DC offset appears in the output, which causes deterioration of distortion rate characteristics, etc., which is undesirable.

In order to suppress such DC offset, the transistor Q5 and the constant voltage source 22 are provided. This transistor Q5 has an emitter connected to the collector of the transistor Q3, a base connected to the second constant voltage source 22, and a collector connected to the collector of the transistor Q7 of the current mirror circuit CM.

That is, the base of the third transistor Q5 is grounded by the base of the first transistor Q5. It functions to equalize the collector-emitter voltages VcK of the second transistors Q3 and Q4, and suppresses DC offset due to the Early effect. however,
The voltage v2 of the second constant voltage source 22 is set to a value higher than the output potential (ie, VE) by the base-emitter voltage VB of the transistor Q5.

As described above, in the amplifier circuit of this embodiment, the differential current based on the input voltage V 1 a of the input signal is controlled by the first . Second transistor Q3. A third transistor Q5 and a collector of the first transistor Q3 are supplied to each base of a common emitter transistor differential pair consisting of Q4, and have a collector connected to the current mirror circuit CM and a base connected to the constant voltage source 22. By connecting the collector of the second transistor Q4 to the current mirror circuit CM, the collector-emitter voltages Vcg of the first transistor Q3 and the second transistor Q4 become the same, thereby eliminating the adverse effects caused by the Early effect. is prevented, and DC offset is removed.

By the way, in the amplifier circuit like this embodiment, the current It of the current sources 10 and 11, the current 1 of the current source 12, etc. By controlling from the outside, the gain of the amplifier circuit itself can be changed. In other words, the circuit of this embodiment can be used as a gain control amplifier.

That is, in the circuit of this embodiment, the transistor Q
l, Q2. Q3. The current between the base and emitter of Q4 is 11-11m+) for the transistor Q1, 1+ +1+- for the transistor Q2, and It/2 for the transistor Q4.
+io/2, transistor Q3 becomes It/2-1o
/2. Therefore, these transistors Ql, Q
2. Q4. The relationship between the base-emitter Mt pressure Vll of Q3 is as follows. In other words, as shown in equation (3), 0...
(3) However, in equation (3), q is the Boltzmann constant, q is the electron charge, T is the absolute temperature, and Is is the saturation current. From this equation (3), the output current! . ■.

I0= ・! 1.・・・・・・・・・
...(4)■1.

Further, as described above, when the circuit of this embodiment is used as a gain control amplifier, the current 1 of the current source 10.11 or the current I of the current source 12 can be varied. In other words, equation (4) and the above (1), (2)
, From equation (3), the current value is 1. , I2 can now be used to determine the gain.

Furthermore, when the current of each current source is varied in this way, the transistor Q4. The current flowing through Q3 will change. At this time, the collector voltage of the transistor Q4 is, for example, the voltage VE. On the other hand, the collector voltage of the transistor Q3 becomes unstable, and these transistors Q3. Each collector-emitter voltage of Q4■. . A difference occurs, and a DC offset appears.

However, according to the circuit of this embodiment, as described above, since the DC offset is removed, the accuracy of the output can be maintained even if the gain is changed. In addition, in this embodiment, the input signal is converted into a current and outputted as a current ratio to the operational amplifier 30 etc. in the latter stage of the circuit, so that the transistor Q1. Q2. Q
3. No amplitude appears at the base of Q4, so a wide dynamic range can be achieved.

〔Effect of the invention〕

In the amplifier circuit of the present invention, the first
and the differential current from the second diode. A third transistor whose collector is connected to a current mirror circuit and whose base is connected to a constant voltage source is connected to the collector of the first transistor. And the second
By connecting the collector of the transistor to a current mirror circuit and taking out the current output from this collector, it is possible to suppress the DC offset.

[Brief explanation of drawings]

FIG. 1 is a schematic circuit diagram of an amplifier circuit according to an embodiment of the present invention, and FIG. 2 is a schematic circuit diagram of a conventional amplifier circuit. Ql, Q2. Q3. Q4. Q5...Transistor CM...Current mirror circuit 21゜22...Constant voltage source

Claims (1)

[Scope of Claims] First and second electrodes each having an input signal supplied as a differential current and having their other ends connected in common and connected to a first constant voltage source.
a common-emitter transistor differential pair consisting of a first transistor and a second transistor whose bases are supplied with differential currents from the first and second diodes, respectively; and a current mirror circuit connected to the collector of the third transistor and the collector of the second transistor, An amplifier circuit characterized in that a current output is taken out from the collector of the second transistor.