AD7134 Calibration in Averaging Mode

Question

Hi, 
 
 I'm using the EVAL-AD7134FMCZ with its evaluation software and I am using the AD7134 Device 0 in Averaging Mode, so the DIGITAL_INTERFACE_CONFIG register is set to 0x0F which means channel averaging. 
 Data from channel 0 and channel 1 are averaged and output on DOUT0. CH2 and CH3 are deactivate, so there should nothing be output on DOUT1. 
 
 When I try to do a channel offset calibration for the averaged signal that is output on DOUT0, do I need to apply the offset to the register CH0_OFFSET_REGISTER or also to CH1_OFFSET_REGISTER? 
 So my question is basically, if the offset is applied before the averaging or after the averaging? 
 
 E.g. the evaluation software shows an offset of -1V, which is -2048000 LSB on channel 0 (which shows the averaged signal of CH0 and CH1), do I need to apply the offset calibration just to CH0_OFFSET_REGISTER or also to CH1_OFFSET_REGISTER? 
 And is the offset with a positive sign? So, to I need to apply +2048000 or -204800 in the signed two's complement register?

JEstayo · Accepted Answer

Hi davlen , 
 The offset is applied after averaging. When using channel averaging for channels 0 and 1, the offset register for CH 0 must be used. While for averaging CH 2 and 3, the offset register of CH 2 should be used. 
 In your example, say you have shorted the input terminals, and read -1V in the evaluation software. 
 Please write -1024000 in the offset register, as an LSB in the offset register adjustment corresponds to 2LSBs change in the digital output. 
 I hope this answers your question. 
 Thanks, Janine)

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AD7134 Calibration in Averaging Mode