Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
1998-08-17
2001-02-06
Shingleton, Michael B (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S051000, C330S126000, C455S241100, C455S246100, C455S253200
Reexamination Certificate
active
06184751
ABSTRACT:
FIELD OF THE INVENTION
This invention is generally directed to amplifier circuits, and particularly to amplifier circuits that may include AGC (Automatic Gain Control).
BACKGROUND OF THE INVENTION
Various kinds of radio receivers include an RF amplifier, the gain of which can be automatically reduced under strong signal conditions by the use of AGC. Without such AGC, circuitry receiving the output of the RF amplifier can become overloaded, resulting in poor inter-modulation performance and other undesirable results.
A conventional RF amplifier
10
with AGC is shown in FIG.
1
. Transistors
12
and
14
are interconnected as a cascode amplifier, with the transistor
12
receiving an RF input signal to be amplified, and an amplified output signal being developed across a tuned circuit
15
. An AGC signal is coupled via an RC network
16
to the base of transistor
14
. As the AGC signal goes low, the collector-emitter voltage of transistor
12
is reduced. This causes the transistor
12
to begin to saturate, thereby reducing the amplifier's gain and the amplitude of the output signal. With this technique, the output of the RF amplifier can be held at a relatively constant level over a wide range of input signal levels. However, changing the amplifier's gain over a wide range does not provide the desired linearity.
The RF amplifier
10
is designed to be used with a single RF frequency band, with the tuned circuit
15
being tuned to the desired band. Multi-band receivers generally require multiple tuned circuits, one for each frequency band to be received, plus switching devices to select the proper tuned circuit for the frequency band to be received. AGC is also preferably provided for all frequency bands, but including AGC control as shown in
FIG. 1
, in addition to the switching devices needed to select the proper tuned circuit, can lead to duplication of circuitry and an undesirably large number of components. The problem of reduced linearity also remains.
REFERENCES:
patent: 2737628 (1956-03-01), Haines
patent: 4757276 (1988-07-01), Ishii et al.
Callaway, Jr. Edgar Herbert
Siomkos John Robert
Dulaney Randi L.
Motorola Inc.
Shingleton Michael B
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