Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2002-09-23
2004-12-28
Nguyen, Khanh Van (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S127000, C330S129000
Reexamination Certificate
active
06836187
ABSTRACT:
BACKGROUND
The present invention is directed towards the technology of signal transmission, and, specifically towards electronic circuits for power amplification.
Mobile communication devices, for example cellular telephones, need to transmit radio frequency (RF) signals at prescribed power levels. The prescribed power levels are dictated by the radio protocol standard under which the mobile device is operating. For example, in a GSM (Global System for Mobile communication) network, a mobile device transmits RF signals to base stations over a wide dynamic range, for example, up to 35 dBm, depending on the strength of the transmitted signal that the base station is receiving.
When transmission is initiated, the mobile device needs to reach the prescribed power level quickly, typically within about 30 microseconds. Further, the power level of the RF output signal must be maintained at the prescribed constant level.
To achieve the transmission power level, mobile devices include power amplifiers to amplify internally generated RF signals (RF input signal, or RF_IN) to RF transmission signals (RF output signal, or RF_OUT) having the prescribed power level. To maintain the power level of the RF output signal constant, a feedback control loop circuit is often used.
FIG. 1
(prior art) illustrates a simplified diagram of an RF amplifier circuit
20
having a known design. Here, a power amplifier
22
amplifies the RF input signal
21
and generates the RF output signal
23
. To hold the power of the RF output signal
23
constant, a feedback control loop
25
is used. In feedback control loop
25
, a resistor
24
connected to the power amplifier
22
is used to sample the current drawn by the power amplifier
22
by detecting the voltage drop across the resistor
24
. The voltage drop is amplified and the amplified voltage is compared with a reference voltage, V
REF
. The reference voltage can be at the prescribed power level. The difference between the amplified voltage and the V
REF
is an automatic power control input voltage V
APC
. The V
APC
is then applied to the power amplifier
22
. This negative feedback loop
25
causes the power amplifier
22
to draw a supply current that is proportional to the V
REF
. The power of the output signal
23
of the power amplifier
22
is proportional to the supply current. The supply current is drawn from a battery illustrated as the battery voltage V
BAT
in FIG.
1
.
In this design, the amplifier circuit
20
has the disadvantage that the voltage drop across the resistor
24
reduces the voltage available to the power amplifier
22
, thus lowering the power added efficiency of the amplifier circuit
20
. In addition, the resistor
24
is a small low-tolerance resistor that can handle a high current. Such resistors tend to be expensive.
FIG. 2
(prior art) illustrates a simplified diagram of an RF amplifier circuit
30
again having a known design. Here, a power amplifier
32
amplifies the RF input signal
21
and generates an output signal
31
that is operated on by a feedback control circuit
35
before being directed to RF output node
33
. In the feedback control circuit
35
, a directional coupler
34
directs most of the output signal
31
to the RF output node
33
, but a portion (“coupled signal”) of the output signal
31
is directed to a detector
36
. The detector
36
detects the peak voltage amplitude of the coupled signal and sends the detected voltage to an error amplifier
38
. The detector
36
generally contains a detector diode and a reference diode. The error amplifier
38
compares the detected voltage, V
DETECTED
, to the V
REF
and generates an amplified automatic power control signal, V
APC
, having a voltage proportional to the difference between V
DETECTED
and V
REF
. The output of the error amplifier
38
is applied to the power amplifier
32
.
In this design, the amplifier circuit
30
has the disadvantage that the coupler
34
reduces the “through output” power of the amplified output RF signal
31
. The “coupled output” power is also reduced. Depending on the implementation, the reduction in through output power by the coupler
34
can be significant, thus decreasing the power added efficiency of the amplifier circuit
30
. Further, the amplifier circuit
30
can be sensitive to temperature in its ability to operate properly. The correlation between the power of the output signal
31
and the V
DETECTED
can change with temperature variations. This is because, in a typical layout, the components of the amplifier circuit
30
are discrete components and that the components are not sufficiently proximal to each other within the amplifier circuit
20
. In fact, components such as the coupler
34
are surface mount (SMT) components that take a relatively large area. Finally, the dynamic range of amplifier circuit
30
is limited. This is because the coupled signal is 10 to 13 dB lower than the output signal
31
. As the power of the output signal
31
decreases, the voltage of the coupled signal can become insufficient to turn on the detector
36
.
Accordingly, there remains a need for an improved power amplifier circuit.
SUMMARY
These needs are met by the present invention. According to one aspect of the present invention, an amplifier circuit includes an amplifier amplifying an input voltage signal to generate an amplified voltage signal and a peak-to-peak detector connected to the amplifier detecting peak-to-peak voltage of the amplified signal to generate a detected signal. A comparator, connected to the amplifier and the peak-to-peak detector, compares the detected signal to a reference voltage signal, generating an automatic power control signal for controlling the amplifier.
According to another aspect of the present invention, an integrated circuit includes a negative peak detector receiving an input voltage signal and generating a first intermediate signal and a positive peak detector. The positive peak detector receives the first intermediate signal and generates a detected signal, the detected signal having value of peak-to-peak voltage of the input signal. The detected signal is substantially a direct current (DC) voltage.
According to yet another aspect of the present invention, a method of amplifying a signal is disclosed. First, an input RF signal is amplified, using an amplifier, to generate an amplified signal. Next, the peak-to-peak voltage of the amplified signal is detected using a peak-to-peak detector. The detected voltage is compared with a reference voltage to produce an automatic power control input signal. Finally, the automatic power control input signal is applied to the amplifier to control the degree of amplification.
Other embodiments and advantages of the present invention will become apparent from the following detailed description, taken in combination with the accompanying drawings, illustrating by way of example the principles of the invention.
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Data Sheet, “Agilent ATF-551M4 LowNoise Enhancement Mode Pseudomorphic HEMT in a Miniature Leadless Package,” dated Nov. 8, 2001, by Agilent Technologies, 24 pages.
Data Sheet, “CGY2015 GSM/DCS/PCS power amplifier,” dated Mar. 12, 2002, by Philips Semiconductors, 24 pages.
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ews/publications/content/file_726.html, 1 page.
Clark Justin Walter
Jansen Bartholomeus Hendrik
Parkhurst Ray Myron
Agilent Technologies , Inc
Nguyen Khanh Van
LandOfFree
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