Methods and systems for power amplifying of signals

Details Methods and systems for power amplifying of signals Methods and systems for power amplifying of signals

2001-03-28

2003-01-07

Pascal, Robert (Department: 2817)

Amplifiers

Modulator-demodulator-type amplifier

C330S20700P, C330S251000

Reexamination Certificate

active

06504426

ABSTRACT:

FIELD OF THE INVENTION
The disclosed technique relates to methods and systems for power amplifying of signals in general, and to methods and systems for power amplifying of audio signals, in particular.
BACKGROUND OF THE INVENTION
Methods and systems for amplifying electrical signals are known in the art. In general, electrical power amplifiers receive a data signal (digital or analog) and produce a respective power amplified analog signal. The type of input signal and the limitations, which are imposed on the output signal, define the structure of the power amplifier and the method, which is used for operating it. Power amplifiers are divided into several classes, according to their structure, such as class A, class AB, class D, and the like.
Conventional power-pushing elements, such as transistors (e.g., BJT, MOSFET, and the like) are made of semiconductor materials. Such power-pushing elements are characterized by a minimal operative voltage (i.e., N-type) or a maximal operative voltage (i.e., P-type). It is noted that in a given configuration, such a power-pushing element is operative to either push current or pull current (i.e., the power-pushing element can deliver current only in one direction).
The type of each of these power-pushing elements inherently limits the voltage levels, which can be amplified thereby. For example, a BJT NPN power-pushing element is characterized by a minimal operative voltage of about 0.7 volts, while defining the input signal as the voltage between the base terminal and the emitter terminal. Accordingly, a BJT NPN power-pushing element can amplify input signals, which are higher than this minimal operative voltage level. It is noted that such a power-pushing element is further limited by a maximal input voltage level, above which it saturates. Most power-pushing elements are also characterized by non-linear transfer functions.
Reference is now made to
FIG. 1A
, which is a schematic illustration of a class A power amplifier, generally referenced
10
, which is known in the art. Class A power amplifier utilizes a single power-pushing element, which pushes current in one direction only, thereby producing only unipolar output signals. For that purpose, class A architecture converts the input signal to a unipolar signal, by shifting it completely either above or below zero level. Class A architecture includes a control unit which overcomes the minimal operative voltage problem and the inherent non-linearity of the power-pushing element.
Amplifier
10
includes a summing unit
2
, a controller
4
and a power-pusher
6
. Summing unit
2
is connected to a constant bias source V
BIAS
, referenced
8
and to controller
4
. Controller
4
is further connected to power-pusher
6
. Summing unit
2
receives an input signal X(t), adds V
BIAS
8
, and provides the result (i.e., X(t)+V
BIAS
) to controller
4
. Controller
4
produces a respective control signal and provides it to power-pusher
6
. Power-pusher
6
produces a power amplified signal Y(t) and provides it back to controller
4
, as feedback. Controller
4
compares the output Y(t) with the elevated input (i.e., X(t)+V
BIAS
) and updates the control signal, so as to correct any errors found between the compared signals.
In general, a class A power amplifier has an output signal with a defined polarity, either positive or negative, according to the type and connectivity of the power-pushing element, which is used therefore. A class A power amplifier is characterized by high quality power amplification in terms of error between the elevated input signal and the output signal.
It is noted that the output of a class A power amplifier is biased. Hence, such a power amplifier can be implemented in systems, which are not sensitive to DC signals, such as audio systems.
The theoretical efficiency of a class A power amplifier, for a full-scale sine shaped signal is 25%. The theoretical efficiency for a full-scale typical speech or audio signal is about 8%. In class A power amplifiers, power is wasted in the form of heat. The power is mainly wasted across the power-pusher, due to the difference between the supplied power source voltage and the output voltage applied to the load.
Class AB power amplifier architecture is a bipolar power amplifier. Class AB architecture includes two power-pushing elements, one for amplifying the positive portion of the input signal and the other for amplifying the negative portion of the input signal.
Reference is now made to
FIG. 1B
, which is a schematic illustration of a class AB power amplifier, generally referenced
20
, which is known in the art. Amplifier
20
includes a controller
22
, a bias power system
24
and two power-pushers
26
and
28
. Bias power system
24
is connected to controller
22
, to the input terminal of positive power-pusher
26
and to the input terminal of negative power-pusher
28
. The output terminals of power-pushers
26
and
28
are connected there between and further to controller
22
.
In the example set forth in
FIG. 1B
, positive power-pusher
26
incorporates a positive power-pushing element (e.g., N-MOSFET, NPN, and the like) and negative power-pusher
28
incorporates a negative power-pushing element (e.g., P-MOSFET, PNP, and the like).
Each of the semiconductor elements used for power-pushers
26
and
28
, exhibits a minimal operative voltage V
1
>0 and a maximal operative voltage V
2
<0, respectively. Together, V
1
and V
2
define a conductance dead zone from V
2
to V
1
. Class AB power amplifier does not allow both power-pushers to operate in the conductance dead zone. In such a situation, both power-pushers do not conduct and hence, the output signal is not defined. Accordingly, bias power system
24
always sets at least one of the power-pushers to conduct current, thereby producing a defined output signal.
Controller
22
receives an input signal X(t), produces a respective control signal and provides it to bias power system
24
. Bias power system
24
modifies the control signal according to the dead zone defined by power-pushers
26
and
28
and provides a positively biased version of the control signal to positive power-pusher
26
and a negatively biased version of the control signal to negative power-pusher
28
. Positive power-pusher
26
produces an output signal Y
1
(t), according to the positively biased control signal provided thereto. Negative power-pusher
28
produces an output signal Y
2
(t), according to the negatively biased control signal provided thereto. The output terminals of power-pushers
26
and
28
are short circuited together to form a common output terminal, producing an output signal Y(t). The output currents of both power-pushers
26
and
28
are summed, thus defining the output signal to be Y(t)=Y
1
(t)+Y
2
(t). Y(t) is fed back to controller
22
. Controller
22
compares the output Y(t) with the input signal X(t) and updates the control signal, so as to correct any errors found between the compared signals.
A class AB architecture, compared with the class A architecture, exhibits lower quality and higher efficiency. The theoretical efficiency of a class AB power amplifier, for a full-scale sine shaped signal is 78.5%. The theoretical efficiency for a full-scale typical speech or audio signal is about 30%. In class AB power amplifiers, power is wasted in the form of heat. The power is mainly wasted across the power-pushers, due to the difference between the supplied power sources voltages and the output voltage applied to the load.
Power amplifying architecture is often influenced by the implementation thereof. For example, class D architecture is directed at situations where either the load is adapted to operate in a limited frequency bandwidth or the receiver of the produced output signal is sensitive to a limited frequency bandwidth. The frequency bandwidth of interest is defined as the cross-section between the load limited frequency bandwidth and the receiver limited frequency bandwidth. Hence, the output signal, provided to the load, can include

Affiliated with

Also associated with

Rating

Methods and systems for power amplifying of signals does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Methods and systems for power amplifying of signals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods and systems for power amplifying of signals will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3062843