Hysteresis-free anti-saturation circuit

DETAILED DESCRIPTION It is accordingly an object of the present invention to avoid saturation over a wide range of received signal strengths.
Another object of the invention is to avoid saturation without loss of receiver sensitivity.
A further object is to avoid saturation without disruption of automatic gain control.
The invented anti-saturation circuit operates in a receiver having a front-end section and a back-end section.
The front-end section receives and amplifies a high-frequency signal, and converts the high-frequency signal to a lower-frequency signal.
The back-end section processes the lower-frequency signal.
The front-end section has a first variable-gain element.
From the lower-frequency signal, the anti-saturation circuit generates an indicator signal that indicates a power level of the lower-frequency signal.
From the indicator signal, the anti-saturation circuit then generates a first control signal that controls the gain of the first variable-gain element.
The gain of the first variable-gain element is made to vary monotonically when the power of the lower-frequency signal is within a certain first range, to remain fixed at a first value when the power of the lower-frequency signal is below the first range, and to remain fixed at a second, higher value when the power of the lower-frequency signal is above the first range.
The gain of the variable-gain element preferably varies in a substantially continuous manner between the first and second values.
The receiver may also have a second variable-gain element, used for automatic gain control.
The anti-saturation circuit then also generates a second control signal that controls the gain of the second variable-gain element.
In one aspect of the invention, the second control signal is held constant when the power level of the lower-frequency signal is within the first range, to compensate for the changing gain of the first variable-gain element.