User manual

...the world's most energy friendly microcontrollers
2012-04-24 - Giant Gecko Family - d0053_Rev0.96 726
www.energymicro.com
• Cascaded Non-inverting PGA
• Two Opamp Differential Amplifier
• Three Opamp Differential Amplifier
• Dual Buffer ADC Driver
• Programmable gain
30.3 Functional Description
The three opamps can be configured to perform various opamp functions through a network of muxes.
An overview of the opamps are shown in Figure 30.1 (p. 726) . Two of the three opamps are part
of the DAC, while the third opamp is standalone. The output of OPA0 can be routed to ADC CH0,
DAC CH0, OPA1 and various pad outputs. The output of OPA1 can be routed to ADC CH1, DAC CH1,
OPA2, and various pad outputs. The output of OPA2 can be routed to ADC CH0, CH5, and various pad
output destinations. All three opamps can also take input from PAD, and OPA0 and OPA1 can also be
connected to DAC CH0 and DAC CH1 respectively.
Figure 30.1. OPAMP System Overview
OPA0
DAC
OPA0OUTn
DAC CH0
OPA0NEXT
OPA1
OPA1OUTn
DAC CH1
OPA1NEXT
OPA2
OPA2OUTn
ADC CH5
input mux
POS0
NEG0
POS1
NEG1
POS2
NEG2
DAC CH0
DAC CH1
ADC CH0
input mux
ADC CH1
input mux
ADC CH0
input mux
A more detailed view of the three opamps, including the mux network is shown in Figure 30.2 (p. 727)
. There is a set of input muxes and multiple output switches for each opamp, making it possible to select
various input sources and various output destinations. The POSSEL mux connected to the positive input
makes it possible to select pad, another opamp output, tap from the resistor network, or DAC as its
source. Similarly, the NEGSEL mux on the negative input makes it possible to select pad or a feedback
path as its source. The feedback path can be a unity gain configuration, or selected from the resistor
network for programmable gain. The output switches connected to the output can be used to route the
output signal to various destinations, including pad, another opamp input, ADC, or into the feedback
path. In addition, there is also a mux to configure the resistor ladder to be connected to vss, pad, or
another opamp output.