Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
1999-11-04
2001-02-06
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S077000
Reexamination Certificate
active
06184728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an output circuit to be used in an amplifier or the like, and relates, more particularly, to an output circuit with an enlarged output dynamic range.
2. Description of Related Art
In general, an amplifier has built therein an input circuit for inputting a signal from the outside of the amplifier and an output circuit for outputting a signal to the outside of the amplifier, and the like.
FIG. 1
is a circuit diagram for showing a conventional output circuit.
The conventional output circuit is provided with a differential amplifier circuit portion
11
having a differential amplifier circuit for producing an in-phase signal and an opposite-phase signal with respect to an input signal, and an output-stage circuit portion
12
having output-stage transistors T
21
and T
22
with multi-stage connections.
The differential amplifier circuit portion
11
has transistors T
23
and T
24
differentially connected to each other. The base of the transistor T
23
is connected to an input terminal of the output circuit. To the collectors of the transistors T
23
and T
24
, resistor elements R
23
and R
24
re connected respectively. Further, to the emitters of the transistors T
23
and T
24
, resistor elements R
25
and R
26
are connected respectively. The resistor elements R
25
and R
26
are connected with a constant current source I
21
for generating a constant current. The base of the transistor T
24
is connected to the connection point of resistor elements R
27
and R
28
connected in series.
In the output-stage circuit portion
12
, an output terminal of the output circuit and a resistor element
21
are connected to the emitter of the output-stage transistor T
21
. A resistor element R
22
is connected to the emitter of the output-stage transistor T
22
. The base of the output-stage transistor T
21
is connected to a connection point “c” between the transistor T
23
and the resistor element R
23
, and the base of the output-stage transistor T
22
is connected to a connection point “d” between the transistor T
24
and the resistor element R
24
.
A positive power is supplied to the resistor elements R
23
, R
24
and R
27
and the collectors of the output-stage transistors T
21
and T
22
. The constant current source I
21
and the resistor elements R
21
, R
22
and R
28
are grounded.
When an input signal of an amplitude V
21
is supplied to the conventional output circuit having the abovedescribed structure, this input signal is amplified into output signals with amplitudes V
22
and V
22
′ respectively by the amplification effect of the transistors T
23
and T
24
. In this case, the output signal V
22
becomes in opposite phase to the input signal, and the output signal V
22
′ becomes in-phase with the input signal, so that the emitter potential of the output-stage transistor T
21
becomes in the opposite phase.
However, there is a problem that the output dynamic range of the above-described conventional output circuit is constrained by a collector-emitter voltage V
CE1
of the transistors T
23
and T
24
within the differential amplifier circuit portion
11
and by a collector-emitter voltage V
CE2
of the output-stage transistor T
21
within the output-stage circuit portion
12
.
In other words, the output dynamic range of the conventional output circuit becomes V
22
≦r23×i21 when the resistance value of the resistor element R
23
is expressed as r23 and the current value of the constant current value I
21
is expressed as i21. However, this output dynamic range is constrained by the collector-emitter voltages of the transistors T
21
, T
23
and T
24
as shown by the following formula 1.
V
22
≦
r
23×
i
21<V
CE1
<V
CE2
(1)
Therefore, for example, when the potential of the connection point “c” becomes low, the emitter potential of the output-stage transistor T
21
also becomes low. Thus, the margin of the collector-emitter voltage V
CE2
of the output-stage transistor T
21
becomes the minimum. As the emitter potential and the collector potential of the output-stage transistor become opposite phase components, the output dynamic range is constrained by the performance (collector-emitter voltage) of the transistor.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an output circuit capable of obtaining a wide dynamic range without depending on the collector-emitter voltage of the transistor.
According to one aspect of the present invention, an output circuit comprises a first transistor connected to an output terminal, a first resistor element connected to the first transistor, a second transistor connected to the first transistor in cascade, a second resistor element connected between the second transistor and the ground, an emitter follower connected to the first and second transistors, the emitter follower having a level shift function, and an input circuit which inputs a first input signal and a second input signal to the emitter follower, the first and second input signals being opposite to each other in phase.
According to another aspect of the invention, an output circuit comprises a first bipolar transistor or MOS transistor whose collector or drain is connected to an output terminal, a first resistor element connected to the collector or drain of the first bipolar transistor or MOS transistor, a second bipolar transistor or MOS transistor connected to the first bipolar transistor or MOS transistor in cascade, a second resistor element connected between an emitter or source of the second bipolar transistor or MOS transistor and the ground, an emitter follower connected to each base or gate of the first and second bipolar transistors or MOS transistors, the emitter follower having a level shift function, and an input circuit which inputs a first input signal and a second input signal to the emitter follower, the first and second input signals being opposite to each other in phase.
According to the above aspects of the invention, signals of mutually opposite phases are input to the first and second transistors, and driving currents of the first and second transistors follow the input signals. Accordingly, it is possible to obtain a wide dynamic range without depending on the performance of these transistors.
Further, the output circuit may comprise a positive power source or a negative power source connected to the first resistor element and the emitter follower.
Furthermore, the emitter follower may have a third transistor to which the first input signal is applied and a fourth transistor to which the second input signal is applied.
REFERENCES:
patent: 4988895 (1991-01-01), Kihara et al.
patent: 5136183 (1992-08-01), Moyal et al.
patent: 6091266 (2000-07-01), Pohlmann
patent: 5243861 (1993-09-01), None
patent: 5267955 (1993-10-01), None
patent: 6177681 (1994-06-01), None
patent: 8316737 (1996-11-01), None
Hayes, Soloway, Hennessey Grossman & Hage, P.C.
NEC Corporation
Tran Toan
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