SAR ADC with Selectable Input Range

[celebrevida]

I am in the middle of designing 8-bit SAR ADC and believe I have mostly understood this architecture.

However, I can only design it for Vin range from 0V to Vmax (where Vmax < Vdd and is a separate input).

The issue is how to design SAR ADC with arbitrary input range from Vin_min to Vin_max (both < Vdd).

Example: Vdd=800mV, Vin_min=250mV, Vin_max=550mV
Vin <= 250mV = 00000000
Vin = 325mV = 01000000
Vin = 400mV = 10000000
Vin = 475mV = 11000000
Vin>= 550mV = 11111111
(something like that)

How can I design SAR ADC to work with an somewhat arbitary Vin range (as opposed to 0V to Vmax)?

 

[barry]

Change the voltage references on the top and bottom of your ladder network, right?

 

[celebrevida]

Change the voltage references on the top and bottom of your ladder network, right?

I am using switched-cap DAC not resistor ladder DAC as part of the SAR ADC.

The actual circuit is an ADC.

 

[nitishn5]

It is still the same,
The VREFP and VREFM that you switch the capacitor bottom plates to. (VREF and 0 if it is single ended)
Change the voltages there.