CODEC AD1836A  ADC verification

CODEC AD1836A AD converter working in differential input mode: ( Gain=1)

We have:

ADC2 Left Input 1=2.25V +small AC signal

ADC2 Left input 2=2.25V

Differential mode setting and gain=1.

The Data sheet says

Full-Scale Input Voltage (Differential) 2.18V ( RMS), 24 bit ADC

My question is :

(1)  If differential input voltage= -0.1V, what is the ADC2 digital output? Is ADC2 unipolar or bipolar?

(2) If differential input voltage=0.1V, what is the ADC2 digital output?

(3) if the differential input voltage is constant DC voltage, then will the ADC 2 output  be zero?

We have experience with other ADC, such as AD7714, but not familiar with ADC for CODEC.

we would like understand, verify and test how CODEC ADC works.


  • 0
    •  Analog Employees 
    on Jan 9, 2018 2:13 AM

    Hello blackfin,

    These are audio specific ADCs where the 7714 is designed for data conversion so there are other options. The 1836A's ADCs are sitting up at a common mode input DC level. The ADC will produce a 2's compliment 24 bit output. So if the input of the ADC is sitting at the 2.5V common mode, it will produce a zero output. (now this is ideal, in reality there is always a DC offset since no converter is perfect.). So 2.5V will produce zero. A slight positive DC signal above 2.5V will produce a positive number. The max is 0x7FFFFF. Note the sign bit is low.

    For a slightly negative number, just one bit negative will produce 0xFFFFFF which is a minus 0x000001 in 2's compliment form. So the maximum negative number possible is 0x800000. Note the sign but is high.

    So if the input is a constant DC offset then it will output a constant number. It can be a positive or negative number depending on the DC voltage as it compares to the common mode voltage of ~2.5V.

    Dave T

  • Second question for AD1836A:

    The datasheet says

    " Full-Scale Input Voltage (Differential) 2.18 (rms) -----------6.16V (V pp)"

     "Vref=2.25V ( common mode)"

    in our differential mode design,  assuming Gain=1, when the differential input voltage is   3.08V,  ADC output will be saturated to the most positive-MAX number , and when the differential input voltage is    -3.08V,  ADC output will be saturated to most negative- MIN number?


  • 0
    •  Analog Employees 
    on Aug 2, 2018 4:00 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin