Method and apparatus for exponential gain variations with a linearly varying input code

A programmable gain amplifier having n gain steps where the n steps, comprising:

• an operational amplifier;
• analog input terminals;
• a charge summing node;
• an array of programmable capacitors programmed to give a first capacitive switching circuit and a second capacitive switch circuit for each of the n steps;
• a first analog output terminal outputting an analog output voltage;
• a first sampling switch coupled to charge the first capacitive switching circuit according to the voltage on the first analog input terminal;
• a first feedback switch coupled to charge the first capacitive switching circuit according to the voltage on the first analog output terminal;
• and
• a second feedback switch coupled to charge the second capacitive circuit to a predetermined voltage;
• wherein
• the first group of steps are each governed by a first gain equation, which determines the capacitance of the first and second capacitance switching circuits, and the second group of steps is governed by a second gain equation, which determines the capacitance of the first and second capacitance switching circuits, the first gain equation being different than the second gain equation.

A programmable gain amplifier having n gain steps, with n being an integer, the programmable gain amplifier comprising:

• an operational amplifier having a first op amp input and a first op amp output;
• a first analog input terminal receiving a differential analog input voltage;
• a charge summing node coupled to the first analog input terminal;
• an array of programmable capacitors, for each step the array of programmable capacitors are programmed to give a first capacitive switching circuit and a second capacitive switching circuit;
• a first analog output terminal coupled to the first op amp output and outputting an analog output voltage;
• a first sampling switch coupled to charge the first capacitive switching circuit according to the voltage on the first analog input terminal, and a first feedback switch circuitry coupled to charge the first capacitive switching circuit according to the voltage on the first analog output terminal whereby the first charge summing node is coupled to receive this charge;
• and
• a precharge switch coupled to charge the second capacitive circuit to a voltage reference level whereby the first charge summing node is coupled to receive this charge
• whereby ‘a’ is a predetermined value of capacitance and ‘x’ is a programmable capacitance value determined by the gain step and the first capacitive switching circuit has an approximate value of (a−x) and the second capacitive switching circuit has an approximate value of (a+2x).