JPH0275209A - Driving circuit - Google Patents

Abstract

PURPOSE:To prevent the occurrence of the distortion due to delay by correcting a base current of a charge/discharge transistor(TR) by a current from a current mirror circuit, connecting a constant current source to the current mirror circuit so as to make the current mirror circuit always operative. CONSTITUTION:Trs 9, 10 are connected in series with the collector and emitter of the charge/discharge TRs 4, 5 and bases of the TRs 9, 10 are connected to bases of the TRs 4, 5 via current mirror circuits 11, 12 and constant current sources 13, 14 are connected to the current mirror circuits 11, 12. Thus, the case current of the charge/discharge TRs 4, 5 is corrected by a current from the current mirror circuits 11, 12 and the constant current source 13 is connected to the current mirror circuits 11, 12 to make the current mirror circuits 11, 12 always operative. Thus, the delay in the signal by the current mirror circuits 11, 12 is reduced and the production of distortion due to the delay is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit used, for example, when charging and discharging capacitance in an A/D conversion circuit.

[Summary of the invention]

The present invention relates to a drive circuit, and when correcting the base current of a charging/discharging transistor via a current mirror circuit, current is constantly passed through the current mirror circuit to prevent distortion due to delay in operation. It is something.

[Conventional technology]

For example, when performing A/D conversion in a digital VTR, a so-called flash type A/D conversion circuit is used. In this case, a capacitor is provided in A/D conversion to hold the input signal, but especially in the case of a flash type, the capacitance is relatively large, for example, about 100 pF (because this capacitance load is A drive circuit for discharging is required.

[Problem to be solved by the invention]

As a drive circuit to charge and discharge such capacitance charge,
Conventionally, for example, a circuit as shown in FIG. 2 has been known. In the figure, the input terminal (21) to which the signal Vin is supplied
is connected to the bases of a pnp transistor (24) and an npn transistor (25) having a 5EPP configuration through an npn transistor (22) and a pnp transistor (23).
) is connected to the load capacitor (26).

As a result, the signal Vin supplied to the input terminal (21)
When is positive, the npn) transistor (25) is made conductive and charge is supplied to the capacitor (26), and the signal V
When in becomes negative, the pnp I-transistor (24) becomes conductive and the capacitor (26) is discharged. In this way, the capacitor (26) is charged and discharged.

However, in this circuit, from Q=CAV=IΔT, when V=A sin ωt, when I is the current value of the current sources (27) (28) connected to the I transistors (22) (23), ■
〉CAω. Here, set C-100pF like two series, and further Vin = 2 VP-p, f = 10Mtlz
Then, T=6.28 mA, and a comparatively large current will be passed through the circuit. When such a current is applied, the distortion rate of the 1-transistor (22) (23) increases, and there is a possibility that a good drive cannot be performed.

By the way, in the above-mentioned circuit, the pnpl' transistor has 7. When , decreases, the base current particularly increases, which has a large effect on the distortion rate. Therefore, as shown in Figure 3, there is an idea to configure the output stage with an NPNL transistor, but although it reduces the distortion rate, it is not a fundamental solution, and this circuit does not have a charge/discharge condition. ) The unbalanced circuit also causes problems such as fluctuations in drive characteristics.

This application was filed in view of these points.

[Means to solve the problem]

The present invention provides a second transistor (9) (1) connected in series to the collector-emitter of the first transistor (4) (5) that charges and discharges a signal charge to a capacitive load (6).
A constant current source (13) is provided to supply the base current flowing through the second transistor to the base of the first transistor via the current mirror circuit (11) (12). This is a drive circuit in which (14) is connected so that current is constantly flowing.

[For production]

According to this, the base current of a charging/discharging transistor is corrected by a current from a current mirror circuit, and by connecting a constant current source to this current mirror circuit, this current I-mirror circuit is kept in a constantly operating state. Therefore, the signal delay caused by the current mirror circuit is extremely reduced, and the occurrence of distortion due to the delay can be prevented.

〔Example〕

In FIG. 1, an input terminal (1
) is connected to the bases of the pnp transistor (4) and the npnl transistor (5) configured in a 5EPP configuration through the npn transistor (2) and the pnl transistor (3), and the emitter connection of this transistor (41 (51) The point is connected to the load capacitor (6).

Further, +71 (81 is the emitter current source of the transistor +21 (31).

Furthermore, a pnp transistor (9) and an npn transistor (10) are provided in series with the collector-emitter of the transistors (41+51), and these transistors (
9) The base of (10) is a current mirror circuit (11,)
(12) is connected to the base of the l transistor (41F5). And this current mirror circuit (11)
Constant current sources (13) and (14) are connected to (12).

In this circuit, the signal V supplied to the input terminal (1)
When in is positive, the npnl transistor (5) is conductive and charge is supplied to the capacitor (6), and at the same time,
At this time, transistor (10) is replaced by transistor (5).
A current equal to that flowing through the transistor (10
) is generated at the base of the base current 110. Here, this base current 110 is equal to the base current I5 of the transistor (5) if the characteristics of the transistor (51 (10)) are equal.
is equivalent to

This base current IIo is passed through the current mirror circuit (12), and the current 114 of the constant current fi (14) is also passed through the current mirror circuit (12), so that the output current ■+z of the current mirror circuit (12) is The value is the sum of these currents.

I 12 = I + o + I 14 This current r+z is supplied to the connection point between the emitter of transistor (3) and the base of transistor (5). In this case, the base current I5 is caused to flow through the transistor (5), and the base current I5 is 15-1+ as described above.

Therefore, the emitter of transistor (3) has 1
Only the constant current of 12 15=II4 and the current ■8 from the constant current source (8) are allowed to flow, and the emitter current Tll of the transistor (3) is TE3-
It becomes a constant current of Is + I +a.

On the other hand, when the transistor (5) is non-conducting, the base current Is, I+. both become O, and the current mirror circuit (
12), only the current 114 from the constant current source (14) is passed through the transistor (
3), the emitter current rE3 of the transistor (3) together with the current I8 from the constant current source (8) becomes IE3 = 18 + IIa, and the emitter current of the transistor (3) is always constant. .

Therefore, according to this circuit, the emitter current of the transistor (3) remains constant regardless of the base current of the transistor (5), thereby eliminating the possibility of distortion occurring.

Note that the transistors (2) and (4) perform exactly the same operation by providing the transistor (9) and the current mirror circuit (11).

Furthermore, in this circuit, a constant current source is connected to the current mirror circuit, so that the current mirror circuit is always in operation, so that the delay of the signal due to the current mirror circuit is extremely small, and the occurrence of distortion due to the delay is minimized. It can be prevented.

That is, in the above circuit, constant current sources (13) (14
), if there is no transistor (41 (51 is A
Since it operates as a class B amplifier, for example, a transistor (
5) enters the active region from non-conducting, the transistor (
Since the base current of lO) flows and that current flows as the collector current of the output transistor of the current mirror circuit (12), the higher the frequency, the more the delay time becomes a problem, and during that delay time, the transistor (2) This affects the emitter current and has the effect of distortion.

In this respect, according to the above-mentioned circuit, a current is passed through the current mirror circuit and the delay time is made as short as possible by keeping the current mirror circuit in a constantly operating state, so that this influence can be minimized.

〔Effect of the invention〕

According to this invention, the base current of the charging/discharging transistor is corrected by the current from the current mirror circuit, and
By connecting a constant current source to this current mirror circuit, the current mirror circuit is kept in constant operation, so the signal delay caused by the current mirror circuit is extremely small, and distortion due to delay can be prevented. Became.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of the present invention, and FIGS. 2 and 3 are diagrams for explaining the prior art. (11 is an input terminal, (2) to (51+91) (10) is a transistor, (6) is a capacitive load, fil f8) (
13) (14) is a constant current source, (11) and (12) are current mirror circuits.

Claims (1)

[Claims] A second transistor is provided that is connected in series to the collector-emitter of the first transistor that charges and discharges a signal charge to a capacitive load, and the base current flowing through the second transistor is current mirrored. A drive circuit that supplies current to the base of the first transistor via a circuit, and connects a constant current source to the current mirror circuit so that a current always flows.