RF switch MMIC behaviour at LF - Page 1
Forum section: electronics / rf-microwave

author: OwO
author_rank: Super Contributor
timestamp: May 02, 2019, 07:48:10 am
content: There are many low cost RF switches that specify frequency range down to ~100MHz, such as the BGS12SN6, that has this curious text in the datasheet: "No decoupling capacitors required if no DC applied on RF lines". This implies the ports operate at 0V DC, and there is no on-chip DC blocking, which means the switch is not diode based but likely use FETs and are similar to analog switch ICs. Does this imply the switch can operate down to very low frequencies (e.g. 10kHz) if I provide appropriately sized DC blocking caps?Background: I'm looking for an RF switch that can operate from near DC (10kHz) to 200MHz. I have found only one part that is specified for DC operation which is the MASWSS0115 and I'm looking for a second source.

author: ejeffrey
author_rank: Super Contributor
timestamp: May 02, 2019, 03:36:07 pm
content: Analog devices has a ton of RF / microwave switches that operate down to DC or near DC, although they are more expensive.https://www.analog.com/en/products/rf-microwave/rf-switches/spst-spdt-sp3t-sp4t-sp6t-sp8t.htmlThe ADG918/919 is $2-3 at mouser but DC to 4 GHz with performance curves down to about 20k. ADG904 is SP4T from DC to 2.5 G.For more money (and you can spend lots more!) you can get much higher frequency, more isolation, and higher pole counts.

author: RadioNerd
author_rank: Regular Contributor
timestamp: May 03, 2019, 06:01:17 am
content: if the upper limit is only 200 MHz you can also take a look at mechanical relays. Operation down to DC, high linearity and power handling and no DC blocking caps required.You could use the kind of signal relays that is also found in scope frontends for example (e.g panasonic TQ series)

author: OwO
author_rank: Super Contributor
timestamp: May 03, 2019, 06:12:47 am
content: So the main requirement is small size and low cost. Max signal power will be less than 20dBm so a relay is overkill. I think I'm going to just make a test board and characterize all those low cost UHF switches from LF to 200MHz.

author: daqq
author_rank: Super Contributor
timestamp: May 03, 2019, 06:17:05 am
content: Take a look at the Analog Devices offerings (https://www.analog.com/en/parametricsearch/11148). They have a lot of nice switches in that area, even MEMS relays.Also, some devices can actually run at much lower frequencies than specified, such as the HMC470A (https://www.analog.com/media/en/technical-documentation/data-sheets/hmc470A.pdf), given bigger external capacitors.

author: dzseki
author_rank: Frequent Contributor
timestamp: May 03, 2019, 08:17:50 am
content: Take a look at SN74LVC1G3157 if it meets your requirements.

author: OwO
author_rank: Super Contributor
timestamp: May 05, 2019, 03:27:22 am
content: Update: I have measured the BGS14GA14 (rated down to 100MHz) down to 1MHz and it does pass the signal through (measured at 0dBm). The insertion loss is slightly lower at the lower frequencies. It seems there is no inherent lower frequency limit in these parts.I'm going to do more testing on the MXD8625 and MXD8641 switches, also the pin compatible BGS12PL6. If these parts prove usable for LF then I can finally switch away from the expensive and hard to source M/Acom switches.

author: OwO
author_rank: Super Contributor
timestamp: May 23, 2019, 06:44:59 pm
content: Update 2: MXD8641 has also been tested to work down to 1MHz with no observable loss or distortion. The isolation is about 10-20dB better than the MACOM switch I was using and at 1/10th the cost