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hello all, I'm testing an analog circuit time-base...
# analog-design
j
hello all, I'm testing an analog circuit time-based which includes a d flip flop, and I would like to replace it by an ideal d flip flop to decouple some issues... is there some way to do this? I found the d_dff digital model on the ngspice, is there any way to: 1. integrate that component in an xschem testbench using a symbol? how do i do the .model and the link to a symbol? 2. integrate it with analog signals using dac_ bridge and adc-bridge' or any other ideas would be really helpful!
t
Yes, that's the right approach. Possibly the quickest way to get there is to use the 
spi2xspice.py
script in 
qflow
, which will convert a SPICE netlist using standard cells into its xspice equivalent subcircuit.
But just to implement a single flip-flop in xspice, you'd want something like this (unverified):
Copy code
.subckt myflop a_vdd a_gnd a_in a_clk a_out

.model todig_3v3 adc_bridge(in_high=2.2 in_low=1.1
+ rise_delay=10n fall_delay=10n)
.model toana_3v3 dac_bridge(out_high=3.3 out_low=0)

.model ddflop d_dff(ic=0 rise_delay=1n fall_delay=1n)

AA2D1 [a_gnd] [d_gnd] todig_3v3

AA2D2 [a_in] [d_in] todig_3v3
AA2D3 [a_clk] [d_clk] todig_3v3

A1 d_in d_clk d_gnd d_gnd d_out NULL ddflop

AD2A1 [d_out] [a_out] toana_3v3

.ends
j
Thanks a lot for confirming, @User I'm trying but no success for now... I still need to find out how to connect this with the xschem symbols, I'll better ask in #xschem
s
@User (@User) i have wrapped Tim's model into a 
ngspice_flop.sym
, as you can see it works. The overall delay is a bit too high so the A/D D/A conversion delays must be lowered somewhat in the model. The new components are available on git
j
Hello @User, WOW, that's great A more basic question: how do i update to get this locally without messing up any dependencies? Just doing the make step again?
Thanks so much by the way
s
@User If you rebuild open_pdks it will fetch the updated xschem sky130 libs including the new flop. However this takes lot of time, cpu, disk activity. Just copy 
ngspice_flop.sch, ngspice_flop.sym, test_ngspice_flop.sch
from git into your open_pdks install, like in: 
..../share/pdk/sky130A/libs.tech/xschem/sky130_tests/
j
Ok, thanks a lot once more, @User
@Alfonso Cortés @Vicente Osorio FYI
@aquiles viza regarding xspice models
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