Semiconductor Devices: JFET Analog Switch

Analog switches can be used in place of mechanical switches for turning on and off small analog signals. The advantages include no moving parts for extended lifespan, "clickless" switching, and remote or programmable switching. In this video we discuss the basic operation of a JFET analog switch along with a more complex variation which exhibits improved performance.
References: Semiconductor Devices: Theory and Application/2E; Chapter 11, Section 7.
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[@LousyPainter]

These configurations are seen a lot where I work. They work very well. Thanks for your videos.

[@ElectronicswithProfessorFiore]

Where do you use them? What are the applications? Always good to have feedback from people in the field.

[@MellexLabs]

I would be very interested in seeing different switching topologies like SPDT and SPTT... is that possible to demonstrate to us? Also... switching between high impedance and low impedance inputs, could that create non-linear behaviour within the switch at various voltages?

[@ElectronicswithProfessorFiore]

Remember, these switches are activated by a control voltage rather than a mechanical linkage. Consequently, you can configure all manner of bizarre configurations. For example, you could have four of these "in parallel" engaging four inputs to four outputs. If you use a common control voltage, they'd all operate in tandem, like a 4PST switch. Of course, you could also invert the control voltage on, say, two of them, so that two inputs contact while the other two don't, and so on. And because it's a control voltage, they can be generated programmatically, e.g., hooking those logic pins back to something like a microcontroller.

[@MellexLabs]

@ElectronicswithProfessorFiore I see so basically to make a single pole multi throw, I would make as many parallel circuits as I need and switch between them in a round robin manner always keeping only one circuit in a logic state high at a time...?

[@ElectronicswithProfessorFiore]

@@MellexLabs You got it.

[@malithamadusankasadaruwan9836]

woooow😮

[@rickybrenay6249]

Seems like the phase is inverted with the analog switch

[@ElectronicswithProfessorFiore]

Vload is in phase with Vin. Functionally, this is no different than a simple resistive divider. The only "inversion" here is the control signal for the middle FET in the improved version.

[@rickybrenay6249]

@@ElectronicswithProfessorFiore yeah, that’s what I was referring to, the improved version. Would that be for the output? Or will it inverter again right before the output? Thanks for the clarifications.

[@ElectronicswithProfessorFiore]

@@rickybrenay6249 There is no inversion of the input signal in either version of the circuit.

[@rickybrenay6249]

Yea that's what i thought too, just at 11:18 mark in the video it shows the sine wave inverted. Thanks again!! @@ElectronicswithProfessorFiore

[@ElectronicswithProfessorFiore]

@@rickybrenay6249 Yeah, that's just leakage. Note that the signal is only about 3 NANOvolts peak-peak! You'd never hear this in an audio application.