356
8331B–AVR–03/12
Atmel AVR XMEGA AU
28. ADC – Analog-to-Digital Converter
28.1
Features
•
12-bit resolution
•
Up to two million samples per second
– Two inputs can be sampled simultaneously using ADC and 1x gain stage
– Four inputs can be sampled within 1.5µs
– Down to 2.5µs conversion time with 8-bit resolution
– Down to 3.5µs conversion time with 12-bit resolution
•
Differential and single-ended input
– Up to 16 single-ended inputs
– 16x4 differential inputs without gain
– 8x4 differential input with gain
•
Built-in differential gain stage
–
1/2
x, 1x, 2x, 4x, 8x, 16x, 32x, and 64x gain options
•
Single, continuous and scan conversion options
•
Four internal inputs
– Internal temperature sensor
– DAC output
– V
CC
voltage divided by 10
– 1.1V bandgap voltage
•
Four conversion channels with individual input control and result registers
– Enable four parallel configurations and results
•
Internal and external reference options
•
Compare function for accurate monitoring of user defined thresholds
•
Optional event triggered conversion for accurate timing
•
Optional DMA transfer of conversion results
•
Optional interrupt/event on compare result
28.2
Overview
The ADC converts analog signals to digital values. The ADC has 12-bit resolution and is capable
of converting up to two million samples per second (MSPS). The input selection is flexible, and
both single-ended and differential measurements can be done. For differential measurements,
an optional gain stage is available to increase the dynamic range. In addition, several internal
signal inputs are available. The ADC can provide both signed and unsigned results.
This is a pipelined ADC that consists of several consecutive stages. The pipelined design allows
a high sample rate at a low system clock frequency. It also means that a new input can be sam-
pled and a new ADC conversion started while other ADC conversions are still ongoing. This
removes dependencies between sample rate and propagation delay.
The ADC has four conversion channels (0-3) with individual input selection, result registers, and
conversion start control. The ADC can then keep and use four parallel configurations and
results, and this will ease use for applications with high data throughput or for multiple modules
using the ADC independently. It is possible to use DMA to move ADC results directly to memory
or peripherals when conversions are done.
Both internal and external reference voltages can be used. An integrated temperature sensor is
available for use with the ADC. The output from the DAC, V
CC
/10 and the bandgap voltage can
also be measured by the ADC.
