Is there any model for Analog Multiplexer compatible with LTSpice or Cadence Virtuoso?
A simple 2:1 multiplexer is implemented in LTSpice as a SPDT switch. So how to implement a 4:1, 8:1 or 16:1 multiplexer?
Electrical – Implementing analog multiplexers in LTSpice and Cadence Virtuoso
cadenceltspicemultiplexer
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If you are referring to a digital mux/demux, then the flow of information is in only one direction, from the input to the output, and the signals are strictly digital. This means that exact voltage levels are not preserved, just logic states. A basic analog switch is SPST, so it can connect two signals together and the flow of information can be in either direction. The resistance of the analog switch is relatively high when the switch is "open" and relatively low when the switch is "closed". An analog mux/demux is basically a collection of N analog switches where one end of all of the switches is connected to a common point. Some digital logic is used to decode the selection inputs and make sure that only one of the N analog switches is closed at any given time. If you set N to be 2, then the analog mux/demux can also be considered an analog SPDT switch. If you set N to four you have an SP4T switch or a 4:1 mux/demux, and so on...
I've used the ADG1401/ADG1402 and the ADG1419 pretty extensively without issues.
The one thing that would give me pause in your application is that the resistance of the iCMOS switches is non-linear with voltage. While I wouldn't worry about using perhaps one or two switches, stringing a lot of them in series could produce some interesting voltage-dependent non-linearities.
With a non-linearity of ~0.5Ω per switch, eight switches would vary ~4Ω across the input voltage range. If the load you're driving is 100KΩ+, it shouldn't be a problem (though some crazy audiophiles will probably disagree).
Realistically, why do you have eight switching elements in the signal path? If I were you, I would try to use fewer larger multiplexers. Analog Devices make 8:1 and 16:1 multiplexers. They have higher on-resistance, but since you have fewer devices, it would balance out.
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Best Answer
Another solution is to use a behavioural source with
table(), such as this:table( V(ctl), 1, V(1), 2, V(2), ... )where
V(ctl)is the controlling voltage supplying various voltage levels, fixed here for clarity, and the nodes labeled as1,2, etc, from which the voltagesV(1),V(2), etc, are taken are the inputs.It's not an ideal solution because behavioural sources tend to suffer from dynamic range fidelity, especially when higher quantities are involved (hundreds of Volts and above), and temporal if the signal has a very large bandwidth. A minor solution is the two hidden parameters,
tripdvandtripdt(see manual, or ltwiki), but they can only do so much.Considering you mentioned VCSW, it should be fairly trivial to implement the switch with more than two switches, for example a complementary pair for each input, or one switch for every input, driven by logic. Not home right now but here's a very quick attempt at the 2nd suggestion:
The pink voltage is the control, the upper pane has the inputs, for comparison with the output below. I've done it so because it seemd to me you're after a behavioural attempt, not a full, real-life scenario; if that's the case, use the 4-pin MOS to build your own transmission gates, for example.