JPH0363246B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to improvements in operational amplifier circuits equipped with current mirror circuits suitable for semiconductor integrated circuits.

[Technical background of the invention]

Conventionally, current mirror circuits constructed as shown in FIGS. 1a, b, and c are known as current mirror circuits used in various semiconductor integrated circuits.

That is, a has first and second PNP transistors Q ₁ and Q ₂ whose bases are directly connected to each other, and Q ₁
This is the most basic current mirror circuit with diode connections on both sides and is widely used.

In addition, b is the PNP transistor Q ₁ in a,
To reduce the diode current error of _Q2 ,
A third PNP transistor _Q3 is added in place of the diode connection of _Q1 .

In order to equalize the collector-emitter voltages of the PNP transistors Q ₁ and Q ₂ in a and b and reduce errors due to the Early effect, c is a third transistor connected in series with Q ₂ , which is the diode-connected side in this case. It has an additional PNP transistor _Q3 .

In other words, when using each of these current mirror circuits, it can be said that c is the most desirable in terms of performance.

[Problems with background technology]

However, in the current mirror circuit using c described above, the collector-emitter voltage of the PNP transistor _Q1 is higher than the base-emitter voltage.
When setting V _BE , approximately 2V _BE ÷ 1.4V is required, so
This poses a problem in that low voltage operation is hindered accordingly.

Furthermore, when the current mirror circuit of c is applied to an operational amplifier circuit as shown in FIG. 2, the constant current source I ₀ of the common emitter circuit of the pair of transistors Q ₄ and Q ₅ for the differential circuit is set small. In this case, the error due to the base current of the output transistor _Q6 cannot be ignored, causing the differential circuit to become unbalanced and causing an offset voltage.

[Purpose of the invention]

Therefore, the present invention was made in view of the above points, and it is possible to operate at as low a voltage as possible, and also to minimize the effects of base current error and early voltage effect caused by subsequent transistors. To provide an extremely good operational amplifier circuit that eliminates unbalance in a differential circuit section and prevents generation of offset voltage by canceling errors caused by base current of output stage transistors using a current mirror circuit improved in the above. It is an object.

[Summary of the invention]

That is, in the operational amplifier circuit according to the present invention, the first transistor is connected to the output side of the differential circuit section, the base of the diode-connected second transistor is coupled to the base of the first transistor, and the first transistor is connected to the output side of the differential circuit section. The emitter of a third transistor is connected to the collector of the second transistor, and the emitter is connected to the base of the third transistor, and the fourth transistor is of a conductivity type different from the first to third transistors. The base of the above first
A current source is connected to the emitter of the fourth transistor, and a fifth transistor, which has the same conductivity type as the fourth transistor and is used for output, is connected to the collector of the third transistor. The bases of the transistors are connected to each other, and the current value of the current source is made approximately equal to the operating current of the fifth transistor for output.

[Embodiments of the invention]

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

That is, in FIG. 3, the input terminal IN connected to the signal source S ₉ is connected to the base of the NPN transistor Q ₁₁ via the capacitor C ₁₁ , and to the other end of the resistor R ₁₁ whose one end is grounded. has been done.

Here, the NPN transistor Q ₁₁ and the NPN transistor Q ₁₂ form a differential pair configuration as a differential circuit section DA, and its collector is directly connected to the power supply V _CC and the common emitter with the transistor Q ₁₂ is connected to the power supply V CC. is connected to the power supply (or ground may also be used) V _EE through a constant current source I ₀ .

Further, the base of the NPN transistor _Q12 is grounded via a resistor _R12 , and connected to the output terminal OUT via a resistor _R13 , and its collector is connected to the collector of the PNP transistor _Q13 .

Here, the PNP transistor Q ₁₃ constitutes a current mirror circuit CM together with transistors Q ₁₄ , Q ₁₅ , Q ₁₆ and a constant current source I ₁ to be described later, and its emitter is directly connected to the power supply V _CC and Its base is connected to the base of PNP transistor _Q14 . Furthermore, the PNP transistor _Q14 is diode-connected, and its emitter is directly connected to the power supply V _CC and its collector is
Connected to the emitter of PNP transistor _Q15 . The PNP transistor Q ₁₅ has its base connected to the emitter of the transistor Q ₁₆ and to the power supply V _EE via the constant current source I ₁ , and its collector connected to the base of the output stage NPN transistor Q ₁₇ . Powered through constant current source I ₂ along with
Connected to V _EE .

In this case, the transistor Q ₁₆ is of a conductivity type NPN different from the PNP transistors Q ₁₃ , Q ₁₄ , and Q ₁₅ .
It is assumed that this has been done.

Further, in the output stage, the NPN transistor _Q17 has its collector connected to the output terminal OUT, and its emitter connected to the power supply _VEE .

In addition, a constant current source _I3 is connected between the power supply V _CC and the output terminal OUT.
is connected.

Of the transistors Q ₁₃ to _{Q 16} that constitute the current mirror circuit CM, Q ₁₃ and Q ₁₄ are transistors that should form a pair, and Q ₁₆ is the transistor that is to be paired with the transistors Q 13 and Q ₁₆ .
It functions as a potential shifter so that both collector and emitter voltages of _Q14 are equalized. Further, in this case, it is assumed that the constant current sources I ₀ , I ₁ , I ₂ , and I ₃ are set in the relationship that I ₂ =I ₀ /2, and I ₁ =I ₃ .

In the above configuration, since the bases of the pair of transistors Q ₁₃ and Q ₁₄ constituting the current mirror circuit CM are directly connected, each base and
The emitter-to-emitter voltages V _BE are equal and the flowing currents are also equal. Furthermore, the currents flowing through transistors Q ₁₄ and Q ₁₅ are also equal.

Furthermore, due to the presence of transistor Q ₁₆ , the collector-emitter voltage V _CE(Q13) of transistor Q ₁₃ becomes V _CE(Q13) = V _BE(Q14) +V _BE(Q15) −V _BE(Q16) ÷V _{BE( Q14)} ÷
0.7 [V], which is equal to the collector-emitter voltage of transistor _Q14 .

In other words, since transistors Q ₁₃ and Q ₁₄ operate with the same collector-emitter voltage, errors caused by the Early (voltage) effect can be minimized.

Furthermore, since the collector-emitter voltage V _{CE (Q13)} of the transistor _Q13 is 0.7V, it is possible to operate the current mirror circuit CM at as low a voltage as possible.

By the way _, in this type _of operational amplifier circuit, the input voltage is Since the bias current is small, the operating current in the first stage is often set to a fairly small value.

On the other hand, the value of constant current source _I3 is usually set to a relatively large value so as to be able to sufficiently drive the load.

In such a setting state, the error due to the base current of the output stage transistor _Q17 cannot be ignored, and the differential circuit section becomes unbalanced, often resulting in an offset voltage.

However, the current mirror circuit as described above
For those equipped with CM, by setting the constant current sources I ₁ and I ₃ to the same value, the transistor
Since the base currents I _{B (Q16) and I B (Q17)} of Q 16 and Q ₁₇ are equal and cancel each other out on the input side and output side of the current mirror circuit CM, the base current of Q ₁₇ It becomes possible to prevent errors caused by I _{B (Q17)} .

In other words, looking at the operating state of the operational amplifier circuit in this case, the operating current of transistor _Q15 is
I _{(Q15) =} I ₂ + I _B(Q17) = I _(Q14) = I _(Q13) , and the operating current of transistor Q ₁₂ I _(Q12)
I _(Q12) (=I ₀ /2) = I _(Q13) −I _B(Q16) , and as mentioned above I _B(Q16) = I _B(Q17) , so I _(Q12) = I ₂ . Here, since I ₂ is set to I ₂ = I ₀ /2 as described above, the current of the constant current source I ₀ flows to 1/2 each of the transistors Q ₁₁ and Q ₁₂ , and the difference is The dynamic circuit section DA will operate in a balanced state, and no offset voltage will occur.

In other words, in the operational amplifier circuit of the present invention, the error caused by the base current of the transistor _Q17 can be canceled out by the base current of the transistor _Q16 in the circuit configuration shown in FIG.

To explain this in a different way, if I ₃ and I ₁ are made approximately equal in Figure 3, the transistor
I _B of Q ₁₇ and I _B of transistor Q ₁₆ are also equal.

I _C(Q15) = I ₂ + I _B(Q17) ...(1) I _C(Q13) = I _C(Q15) . …(2) I _C(Q13) = I _C(Q12) + I _B(Q16) . …(3) Here, I _B(Q17) = I _B(Q16) , and according to equations (1) to (3), I ₂
= I _C(Q12) , and since I ₀ = 2×I ₂ ,
I _{C (Q12)} = I _{C (Q11)} , the differential circuit section DA is balanced, and the offset voltage is minimized.

In this way, the operational amplifier circuit of the present invention uses
It is possible to compensate for not only the variation in current amplification factor (β) of PNP transistors but also the variation in β of NPN transistors.

It goes without saying that the present invention is not limited to the embodiments described above and illustrated, and that various modifications and adaptations can be made without departing from the gist of the invention.

For example, the current mirror circuit CM in the above
In order to prevent oscillation, a capacitor _C12 may be inserted between the collector of the transistor _Q15 and the base of the transistor _Q16 , as shown by the broken line in FIG.

Further, in order to correct errors caused by the current amplification factors β of the transistors Q ₁₃ and Q ₁₄ , a series resistor (not shown) may be inserted in one or both of these bases.

Figure 4 shows the polarity of each transistor in Figure 3.
Another example of mutual conversion such as PNPNPN is shown. In this case, by inserting a resistor R ₁₄ into the emitter circuit of the PNP transistor Q ₁₆ , the DC potential is further shifted, and the collector-emitter voltage of the transistor Q ₁₃ ' is operated in an even smaller state.

FIG. 5 also shows the transistors Q ₁₃ and Q ₁₄ of FIG. 3.
This figure shows another embodiment in which the areas of the emitters are made different. In this case, the transistor
When the emitter area ratio of Q ₁₃ and Q ₁₄ is 1:n, by setting I ₂ n・I ₀ /2, I ₁ = I ₃ /n, the output stage transistor
The influence of the base current of Q ₁₇ can now be canceled out in the same way as in the case of Figure 3.

〔Effect of the invention〕

Therefore, as detailed above, according to the present invention, it is possible to operate at as low a voltage as possible, and
By using a current mirror circuit that can minimize the effects of base current errors and early voltage effects caused by subsequent transistors, the error caused by the base current of the output stage transistor is canceled out, thereby eliminating the unbalance in the differential circuit and generating an offset voltage. It becomes possible to provide an extremely good operational amplifier circuit that does not require any interference.

[Brief explanation of drawings]

FIGS. 1a to 1c are block diagrams showing conventional current mirror circuits, FIG. 2 is a block diagram showing an operational amplifier circuit to which the current mirror circuit of FIG. 1c is applied, and FIG.
The figure is a block diagram showing one embodiment of the operational amplifier circuit according to the present invention, and FIGS. 4 and 5 are block diagrams showing other embodiments. _S9 ...Signal source, IN...Input terminal, _R11 to _R13 ...
Resistor, C ₁₁ , C ₁₂ ... Capacitor, Q ₁₁ - Q ₁₇ ... Transistor, OUT ... Output terminal, CM ... Current mirror circuit, I ₀ - _{I 3} ... Constant current source, DA ... Differential circuit Department.

Claims (1)

[Claims] 1 a differential circuit section, a first transistor connected to the output side of the differential circuit section, a second transistor whose base is coupled to the base of the first transistor and is diode-connected; a third transistor whose emitter is connected to the collector of the second transistor; and a third transistor whose emitter is connected to the base of the third transistor and whose base is connected to the collector of the first transistor; A fourth transistor having a conductivity type different from that of the first to third transistors, a current source connected to the emitter of the fourth transistor, and a base connected to the collector of the third transistor. and a fifth transistor for output having the same conductivity type as the fourth transistor, and the current value of the current source is approximately equal to the operating current of the fifth transistor for output. An operational amplifier circuit characterized by equalization.