differential gain differential phase

[engrvip]

can someone explain about these specs which r used in video ampilifiers.What is their significance in case of video amplifier?and how they r measured during SPICE simulations?And aslo during testing of final IC?

 

[10kangstroms]

Differential gain and phase refer to the change in phase and amplitude of the color subcarrier as a function of the luminance level which the subcarrier is superimposed upon. Differential gain affects color saturation. Differential phase affects hue.
They are typically tested by using what I call the "green ramp". 40 IRE p-p subcarrier is added to a 0-100 IRE luminance ramp. Afer this passes through the video amp, it is fed to a vector scope, where the chroma distortion can be measured.
CAVEAT: I worked in the video industry until about 1993. Some things may have changed since then.

 

[engrvip]

Thanks buddy even this information was helpful.....but can u tell what in case i am designing some monolithic amplifier IC for video applications and then i want to measure these DG DP specs during my simulations.

 

[10kangstroms]

OK, here's one way:
Put an 1 volt AC source on your amplifier's input. Parameterize the DC bias of this source. Do a single frequency AC analysis at the subcarrier frequency while stepping the DC bias voltage through the desired range. For example, if you want to analyze DP and DG for an NTSC signal with no DC offset, run a single-frequency AC sim at 3.58MHz, and step (or sweep) the DC bias on the source from zero to 0.7V. Plot output voltage and phase versus the DC bias voltage. Differential phase will be the peak-to-peak phase variation on the output. Differential gain you can calculate as a percentage of the nominal gain. For example, if the nominal gain is two, and your gain varies from 1.99 to 2.01, your differential gain is 100*(2.01-1.99)/2, or DG=1.0%.

 

[engrvip]

thanks ....this seems useful to me.