JPS6232847B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit that generates a voltage that changes with precisely equal width in both positive and negative directions around a certain reference value.

A drive circuit that generates a voltage that changes with equal width in both positive and negative directions around a certain reference value (including ground potential) is necessary in, for example, a Δ modulation circuit.

Conventionally, drive circuits used for this purpose change the voltage above and below the reference voltage by a width equal to the forward voltage drop V _BE of the diode, for example, by clamping the reference voltage using a diode. Many devices that generate voltage were used.

However, the forward voltage drop of the diode varies logarithmically depending on the value of the current flowing through the diode. Therefore, such conventional drive circuits have the disadvantage that if there is imbalance between the currents in both the positive and negative directions, it is not possible to generate voltages of exactly equal amplitude in the positive and negative directions.

The present invention is a novel invention that eliminates the drawbacks of the prior art, and its purpose is to always generate voltages with exactly the same positive and negative amplitudes. In order to achieve this objective, the drive circuit of the present invention is provided with a current source circuit so that the current value is always kept constant regardless of the direction of the current flowing through the clamp diode. It is characterized in that the voltage generated in the device always changes with exactly equal amplitude on both positive and negative sides.

Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the drive circuit of the present invention. In FIG. 1, transistors T _r1 , T _r2 , and T _r3 constitute a constant current source, and the respective currents i ₁ , i ₂ , and i ₃ are defined by a reference voltage V _ref1 and i ₁ = i ₂ = ki ₃ (1). This means that the ratio of the emitter areas of transistors T _r1 , T _r2 , and T _r3 is k:
This is easily achieved by choosing k:1.

Next, the diode-connected transistor T _r7
and transistor T _r6 form a current mirror,
Current _i4 of transistor T _r6 and transistor T _r7
The current i ₃ is configured such that i ₃ =li ₄ (2). This is easily achieved by choosing the emitter area ratio of transistors T _r6 and T _r7 to be 1:l.

Therefore, if the emitter area of each transistor is selected so that kl = 1/2 (3), the following relationship will always hold: i ₁ = i ₂ = 1/2i ₄ (4).

Further, it is assumed that the transistors T _r4 and T _r5 form a current switch, and the transistor T _r4 is turned on by the input Q, and the transistor T _r5 is turned on by the input.

Now, consider a case where the signal Q becomes higher level than the other signals. In this case, transistor T _r4 becomes conductive as described above, but transistor T _r5
is blocked. Therefore, in this case, the current of the transistor T _r6 serving as a current sink is supplied by the current i ₁ of the current source T _r1 and the current flowing from the reference voltage V _ref2 through the diode D ₂ . diode
The current flowing through D ₂ is equal to the current i ₁ from the relationship in equation (4). Further, the current i ₂ flowing into the reference power supply V _ref2 through the diode D ₄ is also equal to the current i ₁ from the relationship of equation (4). Therefore, the output V _put is _{the forward} voltage _drop (V _B
E ) becomes a higher voltage.

On the other hand, when the signal becomes higher level than the signal Q, the transistor T _r5 becomes conductive and the transistor T _r4 is cut off, and the current of the transistor T _r6 is divided by the current i ₂ of the current source T _r2 and the reference voltage V _ref2 and a current flowing through diode _D3 . The current flowing through the diode D ₃ is equal to the current i ₁ as described above, and the current flowing into the reference power supply V _ref2 through the diode D ₁ is i ₁ . Therefore, the output V _put in this case becomes a voltage lower than the reference voltage V _ref2 by the forward voltage drop (V _BE ) at the current i ₁ of the diode D ₃ .

Generally, the forward voltage drop V _BE of a diode has a relationship with the flowing current i as follows: V _BE = Klni (K: proportionality constant) (5) and changes depending on the value of the current flowing through the diode. However, in the drive circuit of the present invention, the relationship of equation (4) always holds true due to the current mirror, and the current flowing through diode D ₃ and the current flowing through diode D ₄ are always equal. Therefore, the output voltage V _put obtained as the forward voltage drop of the diodes D ₃ and D ₄ is always a voltage with an amplitude exactly equal to the positive and negative sides of the reference voltage V _ref2 .

FIG. 2 is a diagram showing the configuration of another embodiment of the drive circuit of the present invention. In the embodiment shown in FIG. 2, compared to the embodiment shown in FIG. This is the same as in the embodiment shown in the figure.

As explained above, according to the drive circuit of the present invention, an output voltage that always changes in both positive and negative directions with exactly the same amplitude with respect to a reference power source can be obtained, and excellent effects can be obtained when used in a Δ modulation circuit or the like.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are circuit diagrams each showing the configuration of an embodiment of the drive circuit of the present invention. T _r1 , T _r2 , T _r3 , T _r4 , T _r5 , T _r6 , T _r7 ...transistor, D ₁ , D ₂ , D ₃ , D ₄ ... diode,
V _ref1 ...Reference voltage, V _ref2 ...Reference voltage, Q,
...Input signal, +V, -V ...Power supply, i ₁ , i ₂ , i ₃ , i ₄
...Electric current.

Claims (1)

[Claims] 1 A differential pair consisting of two transistors whose emitters are connected in common, first and second transistors forming equal constant current sources connected in series to the transistors of the differential pair, and the first and second transistors each connected in series with the transistors of the differential pair. a first current mirror circuit constituted by a third transistor forming a constant current source with a current ratio of k:1 to the second transistor; a fourth current mirror circuit connected to the common emitter of both transistors of the differential pair; and a fifth transistor in which the current ratio of the fourth transistor is 1:l, and the collectors of the differential pair are connected in both positive and negative directions with respect to a reference voltage. A clamping diode circuit is provided, the third and fifth transistors are connected in series, and the value of kl is halved to obtain a voltage output having a positive and negative value equal to the reference voltage at the collector of the differential pair. A drive circuit featuring: