Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
1999-10-28
2001-08-21
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S282000
Reexamination Certificate
active
06278324
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to analog amplifier circuits with variable signal gain, and in particular, to analog amplifier circuits having variable signal gain according to a monotonic transfer function.
2. Description of the Related Art
Analog amplifier circuits with variable signal gains are used in many applications. One of many examples would be the numerous analog amplifier circuits needed in a video system for processing, conditioning and displaying the video image signals. Indeed, video circuits in particular require such amplifier circuits to have truly monotonic transfer functions with respect to the signal gains. Any nonlinearities or discontinuities in the transfer function can introduce significant signal errors, particularly in high resolution color image displays.
Accordingly, it would be desirable to have an analog amplifier circuit with a variable gain according to a monotonic transfer function and a simple and reliable circuit structure.
SUMMARY OF THE INVENTION
An amplifier with a monotonic transfer function in accordance with the present invention converts an incoming control signal into multiple continuously variable discreet analog control signals for controlling multiple continuously variable circuit impedances connected in a laddered parallel configuration to produce a single continuously variable circuit impedance. This continuously variable circuit impedance, in turn, is used to control the gain of a variable gain amplifier circuit whose transfer function is impedance-dependent. This produces a transfer function which is monotonic. Additionally, a shunt signal attenuation circuit at the input terminal provides additional amplitude control directly for the input signal.
In accordance with one embodiment of the present invention, an amplifier with a monotonic transfer function includes a control signal generator circuit and a variable gain amplifier circuit. The control signal generator circuit is configured to receive a variable input control signal and in accordance therewith generate a plurality of continuously variable discrete analog output control signals having a plurality of respective continuously variable output control signal values including a minimum value, one or more successively greater intermediate values and a maximum value. The variable gain amplifier circuit, coupled to the control signal generator circuit, is configured to receive the plurality of continuously variable discrete analog output control signals and in accordance therewith receive and amplify an analog input signal and in accordance therewith generate an analog output signal, wherein a ratio of the analog output signal and the analog input signal defines a monotonic transfer function.
In accordance with another embodiment of the present invention, the amplifier further includes an input terminal and a shunt signal attenuation circuit. The input terminal, coupled to the variable gain amplifier circuit, is configured to receive from a signal source and convey the analog input signal with an analog input signal magnitude. The shunt signal attenuation circuit, coupled to the input terminal, is configured to receive the variable input control signal and in accordance therewith generate a sink current which has a sink current magnitude and is drawn from the signal source via the input terminal, wherein the sink current and analog input signal magnitudes vary in relation to the variable input control signal.
In accordance with still another embodiment of the present invention, an amplifier circuit with a shunt input signal attenuator includes an input terminal, an amplifier circuit and a shunt signal attenuation circuit. The input terminal is configured to receive from a signal source and convey an input signal having an input signal magnitude. The amplifier circuit has a predetermined signal gain and is configured to receive and amplify the input signal. The shunt signal attenuation circuit, coupled to the input terminal, is configured to receive a variable control signal and in accordance therewith generate a sink current which has a sink current magnitude and is drawn from the signal source via the input terminal, wherein the sink current and input signal magnitudes vary in relation to the variable control signal.
These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.
REFERENCES:
patent: 5828265 (1998-10-01), Mensink et al.
patent: 5936470 (1999-08-01), Stroud
Hojabri Peyman
Morrish Andrew
Dalla Valle Mark A.
Mottola Steven J.
National Semiconductor Corporation
Wildman Harrold Allen & Dixon
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