For the symbol you're showing, it's a simple G source (VCCS) with/without a parallel RC at the output. This is for the
linear flag. In this case,
Vlow don't actually limit the output, rather they specify the threshold over/beneath which the output is attenuated 2x.
Iout is specified, its output is a
tanh() transfer function, and
Vlow are the soft upper/lower limits. You can use
Isink to make the current limits asymmetrical. This could be modeled with a behavioural current source with
tanh(), with/without builtin
Rpar/Cpar parasitics. For the asymmetrical case, you'll need to get creative in creating a complex equation with
If you're using the
mota... symbols, those have two differential inputs, which are multiplied at the output, and there's also the
ref parameter. In this case, the equivalent schematic complicates a bit, but could be done in a "one-liner" in a behavioural expression.
I recommend using the builtin OTA in LTspice, as it performs exquisitely and has no adversary since it's made to be a primitive element (even if specific to LTspice). If you want to implement it in PSpice, most likely you'll need a behavioural approach.
linear case, after fiddling a bit more with the OTA, the limiting is a bit more complicated. It appears that the breaking points are fixed, but the slope is dependent on the gain (
g) and the output resistor (
rout)? At any rate, if you want hard limiting you can use a VCCS with a
table(), or maybe even an ideal diode with custom
vrev, and appropriate
roff (don't forget about
revepsilon for better convergence and, maybe, for a bit of soft-limiting). I'll have to dig up some more, but the asymmetric
tanh() limited version has this formula (
This can be easily implemented in a behavioural mathematical expression, and no external limiting is needed since
tanh() takes care of that, in a beautiful way.
As for the
mota, you have to think a bit differently: there is only one OTA, the one explained on ltwiki.org, which has two differential, multiplying inputs, and all those parameters. The symbols you see in
[SpecialFunctions] are nothing but particuliarities of that one and only OTA:
ota2 are simply the OTA with only the first differential input (symbol displayed with the inputs as
mota2 are the same OTA but now with both inputs -- one differential and one with positive input (they are multiplied one with another), same display (positive/negative inputs, or reverse),
mota3 has the same functionality as
mota2 except the multiplying input is now a differential input, and
mota8 is the full-blown OTA, shown with the additional two pins, the mystical
V-, their functions not precisely determined yet (one has an attempt at an explaination on ltwiki.org). The parameters are common to all variants, since what you see in the symbol browser, or in the schematic, are nothign but symbols making use of that one and only OTA.