surface mount switch with good isolation at 10V - 1MHz - Page 1
Forum section: electronics / beginners

author: raff5184
author_rank: Regular Contributor
timestamp: July 24, 2020, 07:32:35 pm
content: Hi,I have a transmitting device that can generate either signals (3.3V) or power (20V pp) in the rage 500kHz-1MHzOn the receiver side I need to isolate the receiving signal branch when I'm receiving power or it'll burn the device. A surface mount switch or relay would do the job but I can't find one that can isolate properly at those frequencies and "high" voltage. I tried relays like AQY282EH, CPC1114 but they work up to 10kHz.Any suggestions?Thank you

author: awallin
author_rank: Frequent Contributor
timestamp: July 25, 2020, 10:36:23 am
content: TE HF3 relays work up to at least 1 GHzhttp://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=108-98000&DocType=SS&DocLang=ENused in e.g.https://www.ohwr.org/project/rf-mux-8ch/wikis/homethe TASS antenna switch athttps://web.tapr.org/~n8ur/TASS/uses omron g6j-2p-y relayshttps://omronfs.omron.com/en_US/ecb/products/pdf/en-g6j_y.pdfspecified up to 150 MHzmechanical relays are big, clunky, and slow compared to solid-state parts ofcourse...

author: raff5184
author_rank: Regular Contributor
timestamp: July 25, 2020, 11:06:08 am
content: Yes these are quite chunky. I was hoping to find a solid state one and much smaller

author: awallin
author_rank: Frequent Contributor
timestamp: July 25, 2020, 06:35:02 pm
content: if you google for the Rigexpert antenna-analyzers they seem to use e.g. ADG799https://www.analog.com/media/en/technical-documentation/data-sheets/ADG799A_799G.pdfbut that part is not rated for 20Vpp...maybe look at what some SDR-boards (Ettus USRP?) use for switching a single antenna between TX and RX?

author: David Hess
author_rank: Super Contributor
timestamp: July 27, 2020, 05:09:17 pm
content: Does it have to be a single part surface mount solution?Those little plastic enclosed telecom relays are good to 100s of MHz and are commonly specified to 1 GHz.How do HF transceivers which support break-in without relays do it?The isolation requirements can be relaxed by designing a high input impedance RF input stage, which is how oscilloscopes and other high input impedance instrumentation does it.What supply voltages are available?

author: raff5184
author_rank: Regular Contributor
timestamp: July 27, 2020, 08:15:00 pm
content: Quote from: David Hess on July 27, 2020, 05:09:17 pmIt can be a multiple part solution, but the smaller surface it occupies the better.The high voltage (20Vpp) is fixed. I can try to lower it of a couple of volts but not much more

author: David Hess
author_rank: Super Contributor
timestamp: July 27, 2020, 08:43:15 pm
content: Quote from: raff5184 on July 27, 2020, 08:15:00 pmThe reason supply voltage matters is that it limits how far a PIN diode, or any diode, can be biased off. But I assume that PIN diode switches are not suitable because of your low frequency requirement.To meet isolation requirements, a series and shunt switch can be used together.A diode bridge can be used as a low impedance limiter or switch but I do not think this is done in transceivers because of distortion requirements; it works well for 50 ohm oscilloscope inputs though.If a high impedance buffer is used on the receiver, which is very feasible at your frequency range, then simple passive series and shunt protection can protect it against a 20 volt 1 MHz signal, which is how the input protection on a high impedance oscilloscope input works. The disadvantage is higher noise but it does not have to be that much higher.