Differential or single ended input to ADuc7061

Hello,

As described in the datasheet the ADuC7061 accept boths single-ended and differential signals.

I wonder, whether there are any differences _internal_ to the ADC whether a ADC is configured

for a differential or single ended input?

e.g. it is possible via ADC1CH[3:0] to select "ADC4/ADC5(differential mode)" or "ADC4/ADC5(single-ended mode)" - is there any difference?

Best Regards

Norman Werner

  • 0
    •  Analog Employees 
    on Jul 20, 2012 8:22 PM over 8 years ago

    The case that you give of ADC4/ADC5 will be used by ADC1 -

    Differential mode  should be selected for a bi-polar measurement. In this case you will need to set the common mode voltage to maybe 900mV (Bias ADC5 to 900mV).

    ADC5 input will be the negative input and ADC4 input voltage may swing above or below the voltage on ADC5.

    Single ended mode would be suggested for unipolar inputs - where ADC5 is set to 100mV and ADC4 input voltage will always be greater than 100mV.

  • Hi,

    sorry for replying to this old thread, but during a recent project I asked myself the same -- possibly somewhat academic -- question: isn't "ADC4/ADC5 single-ended" mode (0110) internally the same as "ADC4/ADC5 differential" mode (0001)?

    I suppose, yes. I was able to connect ADC5, for example, to 1.7V, ADC4 to 0.7V, and correctly measure -1V regardless whether using differential or single-ended ADC4/ADC5 mode. If I set ADC5 back at AGND, I got 0.7V as the result in both modes.

    The condition to place ADC5 above 100mV stems, from my understanding, from the presense of the negative input's buffer. If that buffer is bypassed using the flag in ADC1CON, it appears to be possible to link ADC5 at AGND too -- that's at least my experience.

    Perhaps all "single-ended" combinations could be considered as differential ones, that happen to share the same negative input pin, ADC5. For comparison, in case of the ADuCM362, where measurements between any two channels may be freely configured, the term single-ended just means, a negative input is shared between multiple measurements, and is possibly connected to AGND.
    The ADuC706x, in contrast, has not the same flexibility regarding input channel combinations: ADC5 is the only reference point for single-ended measurements; that's why the term single-ended here might suggest an actual difference in internal handling. So far, as the two ADC4/ADC5 modes are concerned, that difference didn't seem to be noticable for me.