Where to find an off-the-shelf, passive CMOS RF mixer? - Page 1
Forum section: electronics / projects

author: Odysseus
author_rank: Regular Contributor
timestamp: May 16, 2014, 01:30:24 am
content: I have an existing design and prototype that utilizes a double balanced IQ demodulator (a pair of mixers) that can operate down to DC and is passive (just switches). No gain is required as the input signal is already close to the supply rails. 100 MHz is the fastest signal I'd ever want to bother with. Currently, I've implemented this block using a pair of the fastest SPDT analog switches I could find, the74LVC1G3157, which has a transition time of about 5 ns.I am planning a new design based on lessons learned from the prototype, and I would like to find a mixer/switch IC that contains little more than the schematic shown below. I plan to use it in a circuit which performs down-conversion to DC on a phase varying signal, as shown in the attached LTSpice screenshot.I suspect such a device exists as an RF mixer, but unfortunately I have searched the net with little luck. The closest I've found to a complete IC is theMAX4528Low Voltage Phase Reversal Analog Switch, but it's a little slow and I'd like to avoid all the extra buffering and break-before-make protection. (I discovered it by stumbling across the datasheet someone at work had printed out and left in the office supply room, ha).Any ideas?EDIT:To clarify, I've also attached a screenshot of the wave forms that the device I'm searching for will produce, so others will know straight away what on earth I'm rambling on about.

author: dannyf
author_rank: Super Contributor
timestamp: May 16, 2014, 02:00:34 am
content: "off-the-shelf, passive CMOS RF mixer"The more conditions you pile on, the less options you have.A typical solution would be a diode ring mixer.

author: David Hess
author_rank: Super Contributor
timestamp: May 16, 2014, 03:00:48 am
content: I usually see this done with diode rings or sometimes JFET bridges. Avago sells integrated schottky diode rings but I have never seen integrated FET bridges which would require 6 pins instead of 4.

author: Odysseus
author_rank: Regular Contributor
timestamp: May 16, 2014, 03:07:57 am
content: Quote from: dannyf on May 16, 2014, 02:00:34 amThat description is the closest I can imagine to a marketed device that I'm looking for. That phrase gets me plenty of hits on Google for research papers (no devices though), as well as the image I included.I don't think a diode ring mixer can be DC coupled, can it? That condition can't be relaxed.I could possibly relax the need for rail-to-rail operation, (I.E. NMOS/PMOS only instead of transmission gates.)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 16, 2014, 03:25:28 am
content: Why wouldn't a diode ring mixer work at DC?The main problem I think will be isolation. One port can be at ground, and DC coupled; the others must be AC (transformer coupled), or you need some fancy differential drive circuit.If you need low frequency response at more than one port, probably better to consider something like a single or double balanced mixer (Gilbert cell, or half), or just use a four quadrant multiplier chip (better linearity for audio frequency synthesis, which would be my guess at what you're doing if such were the requirements).I would've thought you were insisting on MOS for extreme dynamic range or something, but if diodes will work...Tim

author: Unknown
author_rank: Unknown
timestamp: May 16, 2014, 03:42:53 am
content: It's getting a little further away from some of your stated requirements, but would anAD831or similar work? DC-200MHz, configurable for 0dB gain, can be DC-coupled on all ports, etc.

author: Odysseus
author_rank: Regular Contributor
timestamp: May 16, 2014, 05:15:09 am
content: Quote from: Tac Eht Xilef on May 16, 2014, 03:42:53 amThanks, I took a look at it and it seems like it could possibly work, but I really only want simple switching action.I did some more hunting and came across thePE4140quad mosfet array. Very close, but probably overkill in speed and too delicate, as I'd like 5V tolerance. Interesting that each mosfet has a threshold voltage of -100mV.