How to measure "small signal Bandwidth" in differe

I want to know how to measure fully differential amp's spec,

I used LMH6550, National semiconductor macro spice model.

I thought I can know How to measure Fully differential opamp' spec if I compare simulation result with LMH6550 datasheet after simulating LMH6550 macro model.

In the LMH6550 datasheet, there is some spec like "small signal -3dB bandwidth", 400MHz

But I got the result only "344MHz" in Hspice simulation.

what do I wrong?


netlist and the result is following

**************************************************

Vdd Vdd gnd dc 5V
Vss Vss gnd dc -5V

X1 in- VCM Vdd out+ out- vss en in+ LMH6550


Rs VIn1 1 50
Rt 1 gnd 50
Rg1 1 in+ 365
Rf1 in+ out- 365
RL out- out+ 500
Rm gnd 2 25
Rg2 2 in- 365
Rf2 in- out+ 365

vin1 vin1 gnd ac 1

Ven en gnd dc 5
Vcm Vcm gnd dc 0

.op
.ac dec 10 10 11000G

*.dc vin1 -5 5 0.1
.print vm(out+) vm(out-)
*.tran 1n 10u
.end

Is the load in the datasheet the same as your simulation? Different load will have different small -signal bandwidth.

Re: How to measure "small signal Bandwidth" in dif

of course.

test condition was referd in the datasheet is following.

single ended in differential out, Av = +1 Vs = +- 5V Vcm = 0V Rf = Rg = 365 RL = 500

but CL is not refered, I did not include it in the simulation circuit

thanks for taking an active interest