关于Hspice仿真放大器差分输出的问题，希望各位大侠可以指点指点我

lucia720

想问下：用Hspice仿放大器，差分输出，我测GBW是不是只要.measure ac gbw  when vdb(vout+)=0就可以了？另外.measure ac gaindb  max vdb(vout+) from  1Meg to 1GHz这个语句测的是差分的增益，还是单端的增益？
我采用的放大器结构是差分输出的。
谢谢！

kmchen3089

You are wrong ! ".measure ac gbw  when vdb(vout+)=0" is referred to signgle ended
GAIN NOT differential gain! I give you one example that I used as the following
and remember that the following is for low output impedance fully differential amplifier
and because it's low output impedance so there is no addition large feed back resistor  to
provide dc operating point  feed back in AC simulation
The example is as the following
***if the fully differential amplifier input common mode voltage is 1.8v
*** and will NOT CAUSE OUTPUT VOLTAGE PULL TO AVDD OR GND
vip   ip 0  dc  1.8v  ac 0.5
vin   in 0  dc  1.8v  ac 0.5 180

***** freq reponse   sweep
.ac dec 100  100  1000meg

****** v(ip),v(in) are input differential signal
****** v(op),v(on) are output differential signal
****** note if we wish to get vdb(op,on)=20log((v(op)-v(on))/(v(ip)-v(in))  
****** then .option acout must be set to "0"
****** if .option acout set to "1" then  vdb(op,on)=20log(v(op)/v(on)
.option acout=0
.probe ac   vdb(op,on)   ****to get vdb(op,on)=20log((v(op)-v(on))/(v(ip)-v(in))

you can try this method with transient simulation
to input specific frequency of differential small signal sine wave at the input of amp and then check differential output voltage and then to calculate differential  voltage
gain in hand to check if my ac simulation is correct!

lucia720

回复 2# kmchen3089


   多谢大侠的指点！！

u123sun

Thank you