200KHz Analog Multipler - Page 1
Forum section: electronics / rf-microwave

author: ricko_uk
author_rank: Super Contributor
timestamp: December 21, 2019, 04:05:02 pm
content: Hi,I have to multiply two signals so I am looking for an analogue mixer/multiplier that:- can work at 200KHz and ideally down to 50KHz- works with a supply voltage down to at least 5V (better if even down to 3V3)- as low cost as possible (need many in a single PCB), ideally less than 1 USD but if not the lowest possibleI am not familiar with this type of ICs (mixers/multipliers) so when googling I could not find much. Could you please offer some parts suggestions and/or pointers so I can search for them.Many thanks

author: German_EE
author_rank: Super Contributor
timestamp: December 21, 2019, 04:41:37 pm
content: I have good news and bad news:https://www.analog.com/en/products/analog-functions/analog-multipliers-dividers.html#Some of these will work with +/- 5V supplies and bandwidth will not be a problem. However, in 1000 quantities prices start at 5 USD a piece and go up from there. The alternative is to feed the two analog voltages into a cheap micro controller, do the math in software, and then output your analog voltage using PWM. Buy in bulk and some manufacturers will even mask program the devices for you.

author: OwO
author_rank: Super Contributor
timestamp: December 21, 2019, 04:43:22 pm
content: SA612 is a Gilbert cell internally and appears to be all DC biased:I would try driving one signal on pin 6, leave pin 7 floating, drive the other signal on pin 1 and AC ground pin 2. Beware that "buffer" may be designed to be saturating.If all fails there are still simple Gilbert cell ICs, or you can even build one with 4 discrete transistors which will work fine below a few MHz.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 21, 2019, 05:06:30 pm
content: The old standard gilbert cell mixer is the MC1496. It is designed to work with some 12 V, but it should be possible to also run at some 5-6 V, though at reduced current / gain and small amplitude.Similar to the SA612 there are other versions for lower power and similar - these may be cheaper.For a lock in amplifier use one does not need a real multiplier. Often a switching mixer, e.g. with CMOS switches like 4053/4052 is even better (less drift, but sensitive to harmonics).

author: erikka
author_rank: Regular Contributor
timestamp: December 21, 2019, 05:45:28 pm
content: SA612 should workLowest supply voltage is 4.5VPin 6 is the osc input, there is a lot of gain in the buffer part, not very linear. Use pin 6 DC isolated as one input.Works best of the the signal to pin 6 is a bit of a square wave and the amplitude of that signal is not important. The conversion gain (from pin1,2 to pin 4,5) is supposed to be independent from the (sufficient) drive on pin 6Leave pin 7 NCUse capacitors to DC isolate both pin 1 and 2, one to your other input and one to ground.Pin 4 and 5 provide the differential output. You can use only on output if low performance requirements. From pin 1,2 to pin 4,5 is a DC path so lowest frequency will only depend on you capacitors or you can even do DCThere is on eBay an offer for 10pcs for less then 6$ from a reputable seller

author: bd139
author_rank: Super Contributor
timestamp: December 21, 2019, 06:12:12 pm
content: SA612 works down to 100Hz easily.The question which is pertinent to ask is what problem are you solving with this? May be cheaper to solve it another way at 1 USD price point.

author: David Hess
author_rank: Super Contributor
timestamp: December 22, 2019, 12:16:19 am
content: The LT1228 variable transconductance amplifier can be used as a multiplier and is way more than fast enough. It operates down to 4 volts.Various operational transconductance amplifiers like the NE5517 and LM13700 may be suitable but are not really intended to operate at low voltages.In the past the CA3102 transistor array was configured as a Gilber cell multiplier.

author: ricko_uk
author_rank: Super Contributor
timestamp: January 02, 2020, 04:34:14 am
content: Thank you OwO,I know what DC bias is but in the case why is it relevant? Does it mean that I can leave pin 2 disconnected? Or what other meaning/advantages does that (being DC biased) have?Thank you

author: OwO
author_rank: Super Contributor
timestamp: January 02, 2020, 07:36:34 am
content: I meant to say DC coupled, meaning there is no lower frequency limit.