Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
1999-05-25
2002-05-21
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S478000, C327S552000
Reexamination Certificate
active
06392454
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an SRPP circuit (shunt regulated push pull).
2. Description of the Related Art
FIG. 1
shows a case in which a sixth order low-pass filter is formed of an active filter. Amplifiers A
1
to A
3
as used are generally formed of voltage followers. The voltage followers A
1
to A
3
(amplifiers A
1
to A
3
) may be formed of (1) emitter followers, (2) SRPP circuits, (3) operational amplifiers, or the like.
Incidentally, the emitter follower of (1) may be structured, for example, as shown in FIG.
2
. That is, the transistor Q
1
has its emitter connected with a constant-current power transistor Q
2
to form an emitter follower, its base supplied with an input signal voltage Vin and a base bias voltage VBB and its collector supplied with a supply voltage VCC. In this way, an output voltage or an output current is extracted from the emitter of transistor Q
1
.
In case of the emitter follower, assuming that the value of the collector current of the transistor Q
2
is IC
2
, as indicated by a solid line in
FIG. 3
, the emitter current IE
1
of the transistor Q
1
varies in proportion with a signal voltage Vin with the value IC
2
as a center. Thus, the amount of variation is extracted as an output.
Hence, as indicated by a broken line in
FIG. 3
, an output current as large as desired can be extracted within a range in which the characteristic of the transistor Q
1
is permitted during a positive half cycle period. However, during a negative half cycle period, an output current larger than the IC
2
cannot be extracted.
The SRPP circuit of (2) can be structured as shown in FIG.
4
. In the SRPP circuit, a signal voltage opposite in phase to the input signal voltage Vin is outputted to the collector of the transistor Q
1
, and the signal voltage is supplied to the base of a transistor Q
2
through a capacitor C
1
. Accordingly, since the transistors Q
1
and Q
2
are driven with phases opposite to each other, the emitter current of the transistor Q
1
and the collector current of the transistor Q
2
vary in directions opposite to each other, and the amount of its difference is extracted as the output current. Accordingly, the SRPP circuit can extract the large output current even during the negative half cycle period.
However, in case of the SRPP circuit, since the base input of the transistor Q
2
is supplied from the collector of the transistor Q
1
through the capacitor C
1
for d.c. cutting, it is necessary to increase the value of the capacitor C
1
in order to extract the large output even in a low frequency.
Accordingly, the SRPP circuit is not proper for implementation as an IC.
From the above viewpoint, the SRPP circuit shown in
FIG. 5
has been proposed. That is, in the SRPP circuit, the collector output of the transistor Q
1
is extracted through the transistor Q
3
that constitutes the emitter follower, and a d.c. voltage is shifted by a constant voltage diode D
1
before being supplied to the base of the transistor Q
2
.
Accordingly, in case of this SRPP circuit, since there is provided no element for limiting the frequency characteristic as in the capacitor C
1
, the frequency characteristic is excellent and a large output can be extracted even in the low frequency.
However, in case of this SRPP circuit, since the d.c. operating point of the circuit is set in accordance with the constant-voltage characteristic of the constant-voltage diode D
1
, if the supply voltage VCC varies, the operating current of the transistors Q
1
to Q
3
largely varies, thereby disenabling the satisfactory characteristic to be obtained. In particular, when the supply voltage VCC is low, such a tendency is high.
In addition, if the operational amplifier is used for the voltage follower, the number of operational amplifiers increases more as the degree is high, thereby making the circuit scale remarkably large. Also, if an amplifier for wide-band frequencies is used in correspondence with applied frequencies, current consumption is caused to increase.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems with the conventional circuit.
To achieve the above object, according to the present invention, there is provided an SRPP circuit comprising:
a first transistor;
a resistor through which the collector of the first transistor is connected to a first reference potential point;
a second transistor having the same polarity as that of the first transistor, the collector of the second transistor being connected to the emitter of the first transistor, the emitter of the second transistor being connected to a second reference potential point; and
a third transistor having the polarity opposite to that of the first transistor, the emitter of the third transistor being connected to the collector of the first transistor and the collector of the third transistor being connected to the base of the second transistor, a bias voltage being supplied to the base of the third transistor;
wherein an input signal is supplied to the base of the first transistor, and an output signal is extracted from a node of the emitter of the first transistor and the collector of the second transistor.
Accordingly, since the third transistor operates with its base being grounded to supply the collector output of the first transistor to the base of the second transistor, the above circuit structure operates as an SRPP circuit.
REFERENCES:
patent: 3892983 (1975-07-01), Okada et al.
patent: 4017788 (1977-04-01), Stepp et al.
patent: 4879506 (1989-11-01), Braun
patent: 5539350 (1996-07-01), Wilhelm
patent: 5952736 (1999-09-01), Matsubara
patent: 8228136 (1996-09-01), None
Lam Tuan T.
Maioli Jay H.
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