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Altera_Forum
Honored Contributor
Honored ContributorTransceiver Pseudo-CML equivalent circuit?
I'm currently testing with the Stratix IV GX development kit and would like to know if anyone has details on the equivalent circuit for the transmitter. A CML driver typically consists of a dif...
Altera_ForumHonored Contributor
Honored ContributorThe other interesting thing that I observe, is that if I change VOD, I change the voltage swing, but not the common mode voltage, ie.,
1. VOD = 3 (default), Vhigh = 910mV, Vlow = 540mV, so Vcm = 725mV and Vpp = 370mV 2. VOD = 0, Vhigh = 800mV, Vlow = 660mV, so Vcm = 730mV and Vpp = 140mV 3. VOD = 7, Vhigh = 1100mV, Vlow = 330mV, so Vcm = 715mV and Vpp =770mV So the common mode voltage is essentially unchanged. If the transmitter was really only able to sink current, then as the sink current is increased, the Vlow voltage should get further from the Vhigh voltage, and the common-mode point should move lower. The observations show that changing VOD increases the peak-to-peak voltage, without changing the common mode voltage. Hence, the transmit buffer is not a simple CML source. Cheers, Dave
