AGC method using digital gain control
An attenuator system includes a first adjustable impedance component on a first current path between a input component and a output component, and a second adjustable impedance component between the first current path and ground, wherein each of the first and second adjustable impedance components include a plurality of selectable, discrete legs, each leg having an impedance.
1 . An attenuator circuit on a semiconductor chip, said attenuator circuit comprising:
an adjustable impedance element with a Radio Frequency (RF) input, wherein said element provides digitally-selectable impedance values in discrete steps; and
digital control lines providing digital signals to said adjustable impedance element, thereby adjusting the impedance thereof and attenuating a signal from said RF input.
2 . The circuit of claim 1 wherein said circuit is included on a silicon chip at the input of a low-noise amplifier, said low noise amplifier also included on said silicon chip.
3 . The circuit of claim 1 wherein said adjustable impedance element includes a set of parallel elements, at least one of said elements selectable by an associated transistor, each said element having an associated impedance.
4 . The circuit of claim 1 further including:
digital control logic operable to measure a power level of said signal from said RF input and to provide said digital signals to said adjustable impedance element to achieve an attenuation based at least in part on said measured power level.
5 . The circuit of claim 1 wherein said circuit is arranged as a voltage divider.