The analog
demultiplexer (FIG. 6) includes an
input amplifier (A1), and output amplifiers (AMP1-AMPN). The output and inverting (−) input of amplifiers (AMP1-AMPN) are connected by a respective
capacitor (C1-CN). Switches (S1a, S1b, etc.) connect the output of
amplifier (A1) to the inverting input of one of (AMP1-AMPN). Switches (S2a, S2b, etc.) connect the output of one of (AMP1-AMPN) to the non-inverting input of the
amplifier A1. Switches (S2a, S2b, etc.) and (S1a, S1b, etc.) open and close together in pairs. With feedback from the output of (AMP1-AMPN) through (A1), the
gain and any offset of (AMP1-AMPN) is divided down by the
gain of (A1).
Amplifier (A1) has capacitors (CS1 and CS2) connected to its inputs. Switch (S50) connects the inverting input of
amplifier (A1) to its output, and switch (S40) connects the non-inverting input of (A1) to a
voltage reference (VREF) matching (VREF) applied to (AMP2). Switches (S30) and (S35) connect (CS1) and (CS2) to the
demultiplexer input (2). In operation, switches (S40, S50, S30 and S35) are initially closed, while switches (S2a, S2b, etc.) are open to charge both capacitors (CS1) and (CS2) and the inputs and output of (A1) to (VREF). Switch (S50) provides feedback to divide down
gain errors and offset of (A1). Switches (S30, S35, S40 and S50) are then open, while one of switches (S2a, S2b, etc.) is closed with one switch (S1a, S1b, etc) to drive one of the output voltages (VOUT1-VOUTN). With inputs and outputs of (A1) and the connected (AMP1-AMPN) initially be at (VREF), very little
settling time is needed.