Gain Stage

The ADC has an internal gain stage, which can be configured to amplify a voltage to allow measurement of smaller voltages in differential mode.

This is a shared gain stage that can be used by all the channels. When the channel is configured to use gain, the gain stage is inserted between the channel input selection MUX and the conversion block. The available gain settings are 1x, 2x, 4x, 8x, 16x, 32x, and 64x. The AVR XMEGA D series can also do 1/2x gain (div2). The Gain Factor bit field (GAINFACT) in the Channel Control register (CHn.CTRL) set the gain factor for the channel. It is possible to have individual gain settings for all the virtual channels.

The propagation delay for an ADC sample through the ADC module increases by one ADC clock cycle flat on the XMEGA A series when using the gain stage, on the XMEGA D series the propagation delay is depended of the gain setting.

To minimize the analog signal path for best possible ADC result it is recommended to disable the gain when not needed.