Amplifiers – With semiconductor amplifying device – Including push-pull amplifier
Reexamination Certificate
2000-08-04
2001-12-11
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including push-pull amplifier
C330S255000
Reexamination Certificate
active
06329878
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to amplifier circuits, and specifically, to high performance amplifier circuits.
2. Background Information
Operational amplifiers of various types are well known in the prior art. Such amplifiers may be characterized as having a differential input of a high impedance, a single-ended output of a low impedance and a high gain, as are generally illustrated in FIG.
1
. Most present day operational amplifiers are required to operate from a single power supply voltage and have an output voltage that is capable of swinging to both supply rails. These amplifiers typically have an input stage that converts the differential input to a single-ended drive for the complementary output drivers. Such an amplifier may be seen in
FIG. 2
, which is representative of prior art amplifiers. In the circuit of
FIG. 2
, the single-ended output of the differential input stage drives the N channel output driver N
1
directly, while P channel device mirrors the current of current source I
1
to the P channel output driver P
1
. The current source I
1
may be an independent current source, representative of class A operation, or as is more common in present day amplifiers, a controlled current source whose current is inversely dependent on the current in output driver N
1
, and hence is representative of class AB operation. Such an implementation of a class AB amplifier that is representative of prior art amplifiers is depicted in FIG.
3
. In the circuit of
FIG. 3
, device N
2
has its gate connected to the gate of device N
1
, and hence its drain current mirrors that of device N
1
. This current flows into the emitter of transistor Q
2
and sets the base-emitter voltage of Q
2
accordingly. Since the sum of the base-emitter voltages of transistors Q
1
and Q
2
is set by the independent current source, I
ref
, flowing through transistors Q
3
and Q
4
, and is therefore constant, the base-emitter voltage of transistor Q
1
, and hence its collector current, will decrease as the current in device N
2
and transistor Q
2
increases, thus fulfilling the requirements for class AB operation.
Furthermore, there are many circuit applications that require analog outputs that are minimally degraded by noise on the power supplies. Examples of these applications include high quality signal processing, signal conditioning, laptop
otebook computers, cell phones and portable headphone speaker drivers. These applications require amplifiers that exist on the same printed circuit board (PCB) with other high speed/high power circuitry and, often, very noisy switch-mode power supplies. These high speed/high power circuits tend to corrupt the power supply voltage, resulting in poor circuit performance. A highly regulated power supply may reduce the effect of noise, but the headroom voltage which is demanded by the regulator is lost for the amplifier and therefore, the output only has a rail-to-rail swing less the headroom loss in the regulator.
Traditionally, an amplifier can either have a good drive capability, i.e., a full rail-to-rail swing but a poor supply rejection or a good supply rejection but poor drive capability. Therefore, there is a need to have an amplifier circuit that has good supply rejection and full rail-to-rail output range without incurring hardware complexity.
SUMMARY OF THE INVENTION
The present invention comprises apparatus and methods to provide high supply rejection and rail-to-rail output swing at the output of an amplifier circuit. A power source supplies power to a low noise regulator and to a differential amplifier output stage. The low noise regulator supplies power to an input stage that is coupled to the output stage, and also provides a reference to the output stage for power supply noise reduction purposes. This configuration of first and second circuits give the output both full rail-to-rail swing and good supply rejection in both stages. Exemplary embodiments are disclosed.
REFERENCES:
patent: 5311145 (1994-05-01), Huijsing et al.
patent: 5337008 (1994-08-01), Badyal
patent: 5521553 (1996-05-01), Butler
patent: 6150883 (2000-11-01), Ivanov
Edwards Christopher F.
Maney J. Williams
Blakely , Sokoloff, Taylor & Zafman LLP
Maxim Integrated Products Inc.
Nguyen Khanh Van
Pascal Robert
LandOfFree
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