samiran_dam said:In one of my earlier post you suggested that, for high frequency filter I need to take care of slew-rate limitation. So, I guess, by calculating the FPBW, I can set the min slew-rate required for a given input amplitude. Am I correct?
`include "constants.vams"
`include "disciplines.vams"
`define PI 3.141592653
module myopamp(vin_p,vin_n,vout,vref);
// small-signal parameters for single-poll roll-off model
//*********************************************************
parameter real gain=10000;
parameter real ugf=10G;
parameter real rin=100M;
parameter real rout=500;
// Large-signal parameters required for slew-rate model
//**********************************************************
parameter i_max = 20u;
parameter real slewrate = 5e6;
parameter real vsoft = 0.05;
input vin_p, vin_n, vref;
output vout;
electrical vin_n, vin_p, vout, inode, vref;
real c_pole, r_pole, gm, vin_max, vin_val;
analog begin
@ ( initial_step or initial_step("dc") ) begin
c_pole = i_max/slewrate;
gm = 2*`PI*ugf*c_pole;
r_pole = gain/gm;
vin_max = i_max/gm;
end
// Input Stage:
//*************
I(vin_p,vin_n) <+ V(vin_p,vin_n)/rin;
// Gain Stage:
//*************
vin_val = V(vin_p,vin_n);
if (vin_val > vin_max)
I(vref,inode) <+ i_max;
else if (vin_val < -vin_max)
I(vref,inode) <+ -i_max;
else
I(vref,inode) <+ gm*vin_val;
// Dominant Pole:
//*****************
I(inode,vref) <+ ddt(c_pole*V(inode,vref));
I(inode,vref) <+ V(inode,vref)/r_pole;
// Output Stage:
//***************
I(vref,vout) <+ V(inode,vref)/rout;
I(vout,vref) <+ V(vout,vref)/rout;
end
endmodule
// Gain Stage:
//*************
vin_val = V(vin_p,vin_n);
if (vin_val > vin_max)
I(vref,inode) <+ i_max;
else if (vin_val < -vin_max)
I(vref,inode) <+ -i_max;
else
I(vref,inode) <+ gm*vin_val;
samiran_dam said:Does the output amplitude limitation come from the output-swing of the opamp? And hence in-turn the input signal handling capacity will put a limit on applied input signal at filter input...right???
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