Amplifiers – With semiconductor amplifying device – Including push-pull amplifier
Reexamination Certificate
2000-11-03
2002-03-05
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including push-pull amplifier
C330S267000
Reexamination Certificate
active
06353362
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to electronic systems and in particular it relates to complementary bipolar operational amplifiers.
BACKGROUND OF THE INVENTION
Resistors needed in the output stage to reduce resonances caused by emitter followers driving capacitive loads cause the current in the output stage to rise quiescently. The prior art output stage circuit of
FIG. 1
shows such an output state. The prior art circuit of
FIG. 1
includes transistors
10
,
12
,
14
, and
16
; resistors
18
-
21
; current sources
22
,
24
,
26
, and
28
; capacitor
30
; positive power supply node
32
; negative power supply node
34
; output node
36
; and ground node
38
. Current sources
22
and
24
each represents a signal dependent current from the input stage of a complementary bipolar operational amplifier. Current sources
22
and
24
provide the DC bias and the input signal to the circuit. Resistors
20
and
21
are needed to damp out the resonance formed by the emitter tuned inductance of transistors
10
and
12
and the base collector capacitances of transistors
14
and
16
and the capacitances of current sources
26
and
28
. To counteract the effect of these resistors on the DC quiescent current, resistors
18
and
19
are added to subtract some voltage from between the bases of transistors
14
and
16
. Resistors
18
and
19
need to be large enough to cause asymmetric phase delays from the gain node to the output. This generates additional stability problems that can lead to the output stage oscillating on its own.
SUMMARY OF THE INVENTION
Generally, and in one form of the invention, the output stage of a complementary bipolar operational amplifier includes: a first bipolar transistor; a second bipolar transistor coupled to the first bipolar transistor; a third bipolar transistor; a fourth bipolar transistor; a first resistor coupled between a base of the first bipolar transistor and the third bipolar transistor; a second resistor coupled between a base of the second bipolar transistor and the fourth bipolar transistor; a first current source; a second current source; a third resistor coupled between the first current source and the third transistor; a fourth resistor coupled between the second current source and the fourth transistor; a fifth resistor coupled between a base of the third transistor and a common node; a sixth resistor coupled between a base of the fourth transistor and the common node; a first input stage current source coupled to the base of the third transistor; and a second input stage current source coupled to the base of the fourth transistor.
REFERENCES:
patent: 4827223 (1989-05-01), Gross
patent: 5302917 (1994-04-01), Concorso
patent: 5578966 (1996-11-01), Mills
patent: 6054898 (2000-04-01), Okuma et al.
Corsi Marco
Gibson Neil
Milam Stephen W.
Brady III Wade James
Nguyen Khanh V.
Pascal Robert
Stewart Alan K.
Telecky , Jr. Frederick J.
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