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# Differential gain and phase measurement setup for Video DAC ( Current Steering)

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#### ashik_na

##### Junior Member level 1
Hi All,
Good Day..!!!
How can we measure the Differential gain error and phase error of a video DAC ( Current steering ) ?
Please explain with simulation setup ...

Thanking You,

For TV work a 5 step waveform is used which has the chrominance subcarrier (4.43 MHz) sitting on it. So as the device has each step going into it, it should continue to amplify both the steps and the sub-carrier equally, but typically as the amplitude of the steps increase the amplitude of the chrominance falls. You view the output via a band pass filter and the chrominance can be seen as 5 blocks of carrier, each of a decreasing amplitude. The first block of carrier is taken as 100% and the lowest one is the measured differentially. first step = 100%, 5 step = 94% diff gain = 6%. Exactly the same with the phase but a special instrument must be used such as the Tektronix vectorscope. You are measuring how the phase of the sub-carrier changes with the level of the steps.
Frank

Thanks ...
But now i am designing a 10 bit CMOS current steering DAC.
So how can i apply the inputs and measure differential phase & gan ?
How can i make a simulation set up for it ?

Is it for video? If it is get yourself the required test equipment, i.e. a Chrominance staircase generator and a gain and delay test set.
If its not for video, build yourself a staircase generator or a low frequency pulse generator with variable amplitude and a carrier generator at your desired frequency and some method of mixing the two. You will also need a band pass filter to filter your carrier out after your piece of kit under test. Set the carrier to 10% of your input level and the pulse to 0%, measure and set the output carrier to 100%. Change the pulse amplitude to 10% and remeasure the output carrier refer it to the 100% reference.... To measure the differential phase do the same but measure the change in phase. You could do this with lissajous(Sp.?) figures on a scope.
Frank

Yes. It is for video application.
How can i measure Differential gain and phase measurement with Spice simulator at transitor level ?

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