Lowest on capacitance switch for SPDT or SPST RF

[john3]

I am looking for a SPDT RF switch (up to 200MHz) with on capacitance <1pF to mount on a PCB. I am thinking it needs to be mechanical but can’t find any RF specs in mechanical data sheets. Any advice?

[APDahlen]

Hello John,

To my knowledge, capacitance is not typically called out on switch or relay datasheets.

As a conversation starting point, have you considered using a hermetically sealed relay such as this?

HFW1201G01M | Digi-Key Electronics

You can find the manufacturer’s data here:

HFW1201G01M : CII Half-Size Relays

Depending on your application, you may be able to uses solid state solution in the form of a PIN diode. Here is a brief introduction using a common1N4148 diode as an example:

Operation of a Diode Based RF Switch: A PIN Diode Demonstration

A diode may be used as a switch for RF frequencies. In this post, we will explore the concept using a common 1N4148 diode. This will allow us to better understand the operation and limitation of the switch circuit. We will conclude with a look forward to the PIN diodes specifically designed for the switching operation. Let’s start with a review of the diode’s internal structure and the bias relationships. Recall that current is free to flow through a forward biased diode. This is simplistically…

Please let us know if we can be of further assistance. If you do, please respond with additional information such as the power level associated with your circuit.

Best Wishes,

APDahlen

[john3]

Hi,
Thank you for the prompt reply! The power level is very low10’s of mW’s at most. The frequency is ~30MHz but there are steps in the signal that we want to observe. The driving circuit is very sensitive to capacitance. I was thinking to use a low profile DIP switch, something like this:

https://www.digikey.com/en/products/detail/nidec-components-corporation/CVS-04TB/948352

But there is of course no spec for capacitance. I did find a solid state differential (which the circuit is too) SPDT (link below) with 1.5pF on capacitance. So, what I’m thinking is to use both, selecting each one with 0 ohm jumpers to see which one works best for this application. If it were me testing I’d just use 0 ohm jumpers and no switch, but unfortunately this isn’t up to me…

https://www.digikey.com/en/products/detail/diodes-incorporated/PSMUX136ZUAEX/18109604?s=N4IgTCBcDaIAoGUCyBVAGgRgMwDYQF0BfIA

Let me know if you have any other thoughts. I’ll probably spend another day looking at low profile DIP switches to see if I can find one with capacitance specs. Then, if not, just do the dual setup I explained above.

thanks again,
John

[APDahlen]

Hello John,

Please let us know if we can assist.

My only thought is to take another look at the PID diode:

Discrete Semiconductor Products | Diodes | RF Diodes | Digi-Key Electronics

It’s a clever low-cost and likely reliable solution for a low power RF system.

Sincerely,

Aaron

[john3]

Oh, I missed the PIN diode capacitance table last time- thanks! Maybe this will work… I’ll let you know once I dive deeper into it.

[David_1528]

We also have a selection of RF rated relays which might be worth a look. Unfortunately, we don’t list the capacitance specs, but most of these are at least in the range of what you’re looking for.

As an example, the 9002-05-00

datasheet shows the following specs:

[john3]

Thanks David, I’ll look into it.
The PIN diode switch won’t work because I need to pass DC through the switch and the diode needs to be AC coupled due to applying the control voltage.

[john3]

Hi again, the PIN diode won’t work because it needs to be AC coupled to apply the control voltage. My application needs to pass DC although there is very little current.