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ADA4930 Common Mode Voltage / Diff-Amp Calculator

Question asked by MatF on Jun 19, 2018
Latest reply on Jun 27, 2018 by JinoL

Hi,

 

I want to use a 1.8 V high speed ADC in combination with the ADA4930. I'm analyzing two signals, one is single ended and the other one is a differential one.

 

According to the dataseeht, the ADA4930 does not create its own input common mode voltage e.g. VDD/2, in single supply operation. Thus for an AC coupled input signal e.g. ±1.5 V, I have to provide the input common mode voltage e.g. with resistors as shown on page 22 in the datasheet. So I tried to analyze the circuit behaviour by two different ways.

 

  1. I downloaded the Spice model and performed a single ended to differential simulation. The input signal swings from +0.5 V to -0.5 V (AC coupled, and no additional bias voltage). Interestingly, the output does not clip, as I would expect as -0.5 V are far below the minimum common mode input voltage of 0.3 V. It seems the Spice model provides its own input common mode voltage, which is equal the output common mode voltage.
  2. I tried to analyze the amplifiere with the Diff-Amp Calculator. Unfortunatly it doesn't works on a Windows 10 OS. Anyway, I have also access to a PC with Windows 7 (64-Bit). I'm using version 4.0.34.8, but it seems some thing went terrible wrong (see attached image). The input and output signals always clipped, and it is not possible to change the output common mode voltage. There are only two values available 8,000 V (8 kV) and -19,000 V (-19 kV).

 

So does the ADA4930 provides its own input common mode voltage (I don't think so), and is the Spice model correct?

 

BR

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