Analog multiplier at > 1 GHz - Page 1
Forum section: electronics / rf-microwave

author: 4a4ik
author_rank: Contributor
timestamp: October 29, 2019, 08:56:45 pm
content: I would like to multiply 2 analog signals, their frequencies are [0Hz 1.5GHz].It's not modulation or demodulation, so I would like to use simple multiplier IC.So far I could only find ADL5391 DC to 2.0 GHz Multiplier.Are there no multipliers IC for high frequencies ?As I understand I can use modulator, demodulator or mixer IC's.Will they work in the same way if I use only multiplier inside them ?If it's possible, should I take into consideration some specific architecture features or parameters ?I am a little bit afraid of phase shifters and LO buffers inside.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: October 29, 2019, 09:07:45 pm
content: So you want to scale a 1.5 GHz signal using a control voltage? You can use a voltage variable amplifier for this, for example ADL5330.

author: 4a4ik
author_rank: Contributor
timestamp: October 29, 2019, 09:33:57 pm
content: No, I need to multiply 2 analog signals.1) I would like to know do people even use multiplication IC's, because I couldn't find them.2) I have to build CDM demodulator, so I need to multiply I and Q channels together (+ filters + delay).schematic attached.3) I would like to know is it possible to multiply 2 signals together using moduletors, demodulators and mixers IC's.Not signal and constant sine wave. But 2 signals.

author: tggzzz
author_rank: Super Contributor
timestamp: October 29, 2019, 09:57:55 pm
content: Now that you have indicated what you want toachieve,rather than how you want todo something, more targeted help can be given.Key figures of merit will probably include minimum and maximum input levels, linearity and intermodulation products.If you don't need DC, then there are many traditional RF techniques for IQ modulators/demodulators. I suggest looking at RF textbooks, application notes, product catalogues, and good quality ham radio publications.

author: 4a4ik
author_rank: Contributor
timestamp: October 30, 2019, 06:42:40 am
content: Ok, but I still would like to get answers to these questions:1) I would like to know do people even use multiplication IC's for wideband signals? Because I couldn't find them.So far I could only find ADL5391 DC to 2.0 GHz Multiplier.There is no task of multiplying wideband signals in RF ?2) I would like to know is it possible to use modulators, demodulators and mixers IC's for that purpose?I am a little bit afraid of phase shifters and LO buffers inside.As I understand LO input is not used for wideband signals.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: October 30, 2019, 10:31:25 am
content: When you say multiplier, is that not exactly what a mixer is? I'm not sure I quite understand what you are trying to achieve here.

author: 4a4ik
author_rank: Contributor
timestamp: October 30, 2019, 10:44:06 am
content: I would like to know if mixer is exactly a multiplier, just with a different name.There is LO buffer inside and mixer usually is used for narrow band signal from oscillator.I need to use wide band signals on both inputs of multiplier.I already found ADL5391 DC to 2.0 GHz Multiplier.But I am interested are there other components which could be used as an > 1GHz multipliers.As I understand modulators and mixers also have multipliers inside, so maybe they can also be used as multipliers.But they work with oscillator * signal, not signal * signal.Modulators have phase changers inside, and mixers have LO buffers.For example mixer AD8343 has LO buffer (image attached).So I have 2 questions:1) Do people use multipliers at RF ? When we have 2 wideband signals, not oscillator and signal.2) Is it safe to use RF mixers, modulators and demodulators to multiply 2 wideband signals together?

author: tggzzz
author_rank: Super Contributor
timestamp: October 30, 2019, 10:57:36 am
content: Quote from: 4a4ik on October 30, 2019, 10:44:06 amAn oscillator's outputisa signal, with a particular set of characteristics.

author: amspire
author_rank: Super Contributor
timestamp: October 30, 2019, 11:24:24 am
content: If am no RF expert, but I will have a go at answering this.Many of the active mixers are linear multipliers. Many are based on circuits such as the Gilbert Cell.However, any non-linear device such as a diode can also be used in a mixer, and it does multiplication - sort of.If you have two pure signal sources - say 1MHz and 1.2MHz and you put them into a perfect linear multiplier, you get two and only two output frequencies - 200KHz and 2.2MHz.If you use a non-linear device in a mixer, you can get a huge number of output components. As well as getting the source signals coming through the mixer (ie 1MHz and 1.2MHz), you can get the intermodulation products of all the harmonics of the two input signals. This can sometimes be quite OK in that you can use a sharp bandpass filter to pick the one output harmonic product you want and you totally ignore all the other junk.If you make the non-linear mixer symmetrical so it behaves the same in positive and negative directions, you eliminate all even harmonics of the input frequencies from the output products. Perhaps two matched diodes.If you make a balanced mixer (perhaps 4 matched diodes in a bridge), you can eliminate the two input frequencies from the output.So the ideal mixer is a linear multiplier, but for use in RF work, you can often use non-linear circuits to do an equally good job by using a sharp bandpass filter (usually called the IF filter) to clean up the very messy output from the mixer.

author: duak
author_rank: Super Contributor
timestamp: November 01, 2019, 06:41:06 pm
content: I would consider a multipler to have a DC to whatever frequency response and have a transfer function that primarily outputs the product of the inputs with few artifacts. OTOH, a mixer could be implemented as a multipler but it's most often done with some non-linear device that isn't so clean.I used an AD734 10 MHz multiplier as an instantaneous real time low frequency power meter. The cost of the chip ($30.-??) was worth it even though I didn't need the DC or high frequency response. Alternatives were to fiddle around with matching transistors or some sort of servoed thermal sensor. I wonder how well it would work for a direct conversion receiver?

author: Marco
author_rank: Super Contributor
timestamp: November 01, 2019, 07:26:04 pm
content: Quote from: 4a4ik on October 30, 2019, 06:42:40 amNot much, proper generic multiplication is an ultra-broadband operation (mixing is only multiplication in a very loose sense). Be glad there is one IC which gets remotely close to what you want to do and count yourself very lucky.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: November 02, 2019, 09:02:08 am
content: Mixers are multipliers in the sense that if you make a taylor decomposition of non-linear transfer functions, you get a power series. If your input is now a(t)+b(t), you get some term (ignoring the others) like (a(t)+b(t))^2, which gives you a(t)^2+b(t)^2+2a(t)b(t). This 2a(t)b(t) is the term we tend to use a lot in standard mixers. You can also get higher order terms, which you use in (sub)harmonic mixers.The key is that you want the non-linear transfer function to be such that either all your other terms are suppressed as much as possible and/or to try and design the spectral content of signals a(t) and b(t) in such a way that your resulting products are in different frequency bands and you can filter out the undesired ones.