.PS
include(libcct.m4)
cct_init

# Usual defs...
qrt=dimen_/4;
hlf=dimen_/2;
dim=dimen_;

ground(,T)
source(up_,AC); rlabel(,v_i,)
line up_ hlf then right_ hlf

Op1:opamp(right_,,,,P) with .In1 at Here
line from Op1.In2 left_ dim
dot "$V_\mathrm{ref}$ sp_ " ljust_
resistor(up_);llabel(,R_1,)
dot; {move up_ 0.1*dim; "$V_s$" ljust_}

move down_ dim
resistor(down_); rlabel(,R_2,); ground(,T)
move to Op1.Out; line right_ qrt; " $v_0$" ljust_

"\tiny Comparator" at (dim, 0) ljust_ 
.PE