Date: Mon Mar 05 2001 - 03:32:56 PST
I have few queries regarding the Differential input parametrics given in
HSTL JEDEC standard.
According to the standard.
Differential input dc logic levels
Symbol Parameter Min. Max.
------ --------- --- ----
Vin(dc) DC input signal voltage -0.30 VddQ+0.30
Vdif(dc) DC differential input voltage 0.20 VddQ+0.60
Vcm(dc) DC common mode input voltage 0.68 0.90
> VddQ is the output supply voltage =1.5V for HSTL
> Vref=0.75 nominal, 0.68 min., 0.90 max. for HSTL
> Vdif(dc) specifies the minimum input differential voltage(Vtr-Vcp)
required for switching where Vtr is the true input level and Vcp is the
complement input level.
> Vcm(dc) specifies the maximum allowable range of Vtr-((Vtr-Vcp)/2)
My questions are
1. If I design a differential amplifier, how i check it for Vdif. I mean
under this condition (checking for Vdif) what type of input i should give
to a diff. amp. Is both Vref input and other input are varying in this
case. What type of output should i get.
2. What is the significance of Vcm. Is it the same as that of common mode
range of a differential amplifier (the range b/w diff. amp. works
linearly ie. transistors are in saturation region).
If not, then how it is taken into consideration while designing.
How is it measured?
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