Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2002-09-26
2004-08-31
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S129000, C327S534000
Reexamination Certificate
active
06784744
ABSTRACT:
BACKGROUND
The present invention relates to electronic circuits and systems, and more particularly, to electronic circuits and systems including amplifier circuits and methods of operating the amplifier circuits.
Amplifier circuits and methods find many applications in electronic systems. For example, amplifier circuits are widely used in wireless communication devices such as pagers, cellular phones, or cellular base stations to process various analog signals within the system. The function of an amplifier is to increase the power, voltage, or current of signals received at the amplifiers input or inputs. One common application of an amplifier circuit is for transmission of a Radio Frequency (RF) signal. For example, many wireless communication systems require a power amplifier to drive the antenna of the system, thereby transmitting information contained in the amplified signals into the airwaves.
FIG. 1
illustrates a conventional MOSFET RF amplifier
100
for amplifying the power of an RF signal. The amplifier circuit
100
includes an input matching network
110
, a MOS transistor
120
, a load
130
, a bias network
140
, and an output matching network
150
. The bias network includes a pair of resistors
141
and
142
connected in series between a fixed bias voltage +V
B
and the gate of MOS transistor
120
. The first terminal of a capacitor
143
is connected to the node between resistors
141
and
142
, and the second terminal of the capacitor
143
is connected to ground.
FIG. 2
illustrates a conventional N-channel MOS transistor structure
200
that may be used in the amplifier circuit of FIG.
1
. MOS transistor
200
includes a body region comprising a P-type substrate
210
, a N-type source region
221
, a gate
230
, and an N-type drain region comprising N− region
242
and N+ region
241
. The drain, source, and body regions include electrical contacts
240
,
220
, and
250
, respectively. In typical amplifier designs using MOS or equivalent devices, the body is electrically connected to the source. A common technique for establishing the source to body connection is a polysilicon connection
260
between the source contact
220
and body contact
250
. Thus, in typical amplifier designs, the body is maintained at the same voltage as the source.
The circuit shown in
FIG. 1
is representative of a single MOSFET amplifier stage. This can be considered a single ended stage or half of a balanced stage. Load
130
may comprise an inductor, shown as j&ohgr;L
1
, which may have a high impedance at the circuit's frequency of operation. As is the case with inductors, any sudden change in current will cause a voltage of opposite polarity to be generated. The magnitude of this voltage will be proportional to di/dt.
Also shown in
FIG. 1
is an input signal
101
. Input signal
101
includes a first amplitude signal portion defining a first signal envelope
102
, and a brief large amplitude pulse portion defining a second signal envelope
103
. Such signals may be common in a variety of electronic systems. For example, in a wireless communication system, such signals may occur when the various wavelengths in an encoded signal constructively interfere. Signals including brief pulse envelopes are problematic to amplifiers because, typically, the amplifier is biased to handle the smaller envelope
102
. Thus, the bias current drawn by amplifier circuit
100
will be primarily determined by the smaller constant amplitude signal. However, when a large amplitude pulse is received, there will be a definite di/dt present across the inductor. The magnitude of the di/dt will depend on the slope of the large amplitude pulse. A large slope will typically cause a large voltage to appear across the inductor, and thus, the output of the amplifier will clip at the supply voltage. Accordingly, any information carried in the input signal
101
may be lost or severely distorted.
Another problem with conventional amplifier circuits and methods is that various electronic system applications, such as wireless communication systems, for example, have an ever increasing requirement that the amplifiers include more functionality and improved performance. For example, electronic systems may require amplifier circuits or methods that have variable gains, wide bandwidths, process or temperature compensation, improved linearity, or power efficiency.
Accordingly, amplifier circuits and methods that have improved performance and increased functionality are desirable for modern electronic systems.
SUMMARY
Embodiments of the present invention provide an amplifier circuit and method that can be used to save power in an electronic system. In one embodiment, the present invention includes an amplifier circuit comprising a transistor having a gate terminal, drain terminal, and body terminal, a load coupled to the drain terminal of the transistor, an input signal coupled to the gate terminal, the input signal including a first signal envelope during a first time period and a second signal envelope during a second time period, a control signal coupled to the body terminal, the control signal including a first signal portion that sets a first voltage on the body terminal and a second signal portion that sets a second voltage on the body terminal, wherein the control signal is synchronized in time with the input signal so that the first signal portion occurs during to the first signal envelope, and the second signal portion occurs during to the second signal envelope.
In another embodiment, the present invention includes an amplifier circuit comprising an amplifier input terminal for receiving an input signal, a transistor having a gate terminal, drain terminal, and body terminal, the gate terminal being coupled to the amplifier input terminal, a load coupled to the drain terminal of the transistor, a body conditioning circuit having an input coupled to the amplifier input terminal and an output coupled to the body terminal of the transistor, the body conditioning circuit including a threshold detector to detect an envelope of the input signal and generate a control signal to change the bias current in the amplifier in response to changes in the envelope of the input signal.
In another embodiment, the present invention includes a method of controlling an amplifier comprising receiving an input signal at the gate terminal of at least one MOS transistor, the input signal including a first signal envelope during a first time period and a second signal envelope during a second time period, receiving a control signal at the body terminal of the at least one MOS transistor, the control signal including a first signal portion that sets a first voltage on the body terminal and a second signal portion that sets a second voltage on the body terminal, wherein the control signal is synchronized in time with the input signal so that the first signal portion corresponds to the first signal envelope, and the second signal portion corresponds to the second signal envelope.
In one embodiment, the present invention provides an apparatus and method for use in a wireless communications system. For example, in one embodiment, the present invention provides a wireless communication system comprising a baseband processor for encoding a communication signal, a modulator coupled to the baseband processor for receiving the encoded communication signal and generating an RF signal, an RF amplifier coupled to the modulator for receiving the RF signal, the RF amplifier comprising a field effect transistor and a load, and a body modulation circuit having an input for receiving the encoded communication signal and an output coupled to a body terminal of the transistor.
In another embodiment, the present invention provides a method of transmitting a signal for use in a wireless communication system, the method comprising encoding a signal in a baseband processor, modulating the encoded signal to produce an RF signal, and amplifying the signal in an RF amplifier, the amplifier including a transistor and a load, wherein
Choe Henry
PowerQ Technologies, Inc.
Townsend and Townsend / and Crew LLP
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