A gain-control method and device that enable high-speed gain switching of cascaded
programmable gain amplifiers (PGA) without a high-resolution A/D converter is provided.
In one example, the gain-control method for cascaded PGAs detects all the input
levels of the PGAs, calculates the optimum gains of the PGAs each on the basis
of the detection results, and sets the obtained optimum gains of each of the PGAs
at one time, whereby high-speed gain switching becomes possible. The gain-control
device for cascaded PGAs that implements this gain-control method includes peak
hold circuits that retain the input levels of each of the PGAs, a switch group
that sequentially switches outputs of the peak hold circuits, an A/D converter
that sequentially detects the outputs from the switch group, and a control and
operation device that calculates the optimum gains of the PGAs from the detection
results by the A/D converter to set the calculated optimum gains simultaneously
to each of the PGAs.
