High Gain Instrumentation Amplifier

In this mode, OPAMP0 and OPAMP1 are configured as non inverting amplifiers [Stage 1]. OPAMP2 is configured as difference amplifier[Stage 2]. Total gain of the instrumentation amplifier is product of gains of stage 1 and stage 2. The OPAMPCTRLx and RESCTRL registers can be configured as follows:

Table 1. Instrumentation Amplifier Configuration
  MUXPOS MUXNEG RES1MUX POTMUX RES2VCC RES2OUT RES1EN ANAOUT
OPAMP0 0000 001 100 111 0 1 1 0
OPAMP1 0000 001 100 111 0 1 1 0
OPAMP2 1000 001 010 111 0 1 1 0
Table 2. Resister Control Configuration
RES1MUX POTMUX RES2OUT RES1EN
0 (DAC) 111 1 1
1 (REFBUF) 111 1 1

The resistor ladders associated with OPAMP0, OPAMP1, OPAMP2 and RESCTRL must be configured as follows in order to select the appropriate gain:

Table 3. Instrumentation Amplifier Gain Selection
OPAMPCTRL0.POTMUX OPAMPCTRL1.POTMUX STAGE 1 GAIN OPAMPCTRL2.POTMUX RESCTRL1.POTMUX STAGE 2 GAIN
0x7 0x7 16 0x7 0x7 15
0x6 0x6 8 0x6 0x6 7
0x5 0x5 5 + 1/3 0x5 0x5 4 + 1/3
0x4 0x4 4 0x4 0x4 3
0x3 0x3 2 + 2/3 0x3 0x3 1 + 2/3
0x2 0x2 2 0x2 0x2 1
0x1 0x1 1 + 1/3 0x1 0x1 1/3
0x0 0x0 1 + 1/7 0x0 0x0 1/7

The RES3TAP potentiometer can be selected as a positive input for the OPAMP2 and the resistor ladder can be connected to OA0OUT by setting the RESCTRL.RES2OUT bit in order to configure OPAMPs as a High Gain Instrumentation Amplifier.

Figure 1. High Gain Instrumentation amplifier
Parent topic: Built-in Modes