# Voltage multiplier

Discussion in 'Homework Help' started by Josato, Nov 7, 2012.

1. ### Josato Thread Starter New Member

Mar 8, 2011
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0
Hi all!

As part of a group project I have to design a circuit that involves a frequency mixer in cadence allegro.

I have to do this to exploit the fact that cos(A)*cos(B) = 1/2(cos(A+B) + cos(A-B)).

Anyway, for the moment I just put in an analogue behavioral model mixer, which does the job perfectly https://en.wikipedia.org/wiki/Frequency_mixer . What I have to do next is replace that component with a circuit.

I have looked for circuits, but I don't know what is really suitable for the project. I have opamps and p and n type mosfets available to use (don't really know what the type is or whether it matters).

Sadly, there is also a current limit on the design so that's something I have to factor in too. Can anyone help? I see that a 'gilbert cell' does the job, but I can't find a mosfet implementation. Why is a voltage controlled amplifer not ok?

If anyone could help or pointers (or even feedback on my question phrasing), I would be extremely appreciative (I know this doesn't translate to much, but there you go)

Jo

2. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
The circuit you want is called a mixer. It does multiplication and produces sidebands at A+B and at A-B. Were you expecting some kind of magic?
Minicircuits and others make such circuit components.

3. ### Josato Thread Starter New Member

Mar 8, 2011
17
0

Yes, but the idea isn't that I purchase a mixer, it is that I design one using op-amps and/or possibly MOSFETs

Feb 24, 2006
10,340
1,850
5. ### Josato Thread Starter New Member

Mar 8, 2011
17
0
Diodes and transformers... I suppose I will have to ask the tutor. I did see that a few designs used diodes and transformers though.

There is a diagram of applying both the signals to a dual gate MOSFET... I can't synthesize one out of the MOSFET I have can I? And I can only use MOSFETS and FETs interchangeably if they are only used for switching?

That isn't a circuit I can build, is it?

6. ### Josato Thread Starter New Member

Mar 8, 2011
17
0
Hi,

I got in contact with the tutor and he suggested using a 'switched gain demodulator'... But when I google it I don't get any results. What is that?

I think I know what the principle is: you multiply your signal by 1 or -1 based on the frequency of modulation you want, and that is like mixing. Only question is, how to do?

7. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
Have you considered an NMOS or BJT balanced modulator? Google LM1496.

8. ### Josato Thread Starter New Member

Mar 8, 2011
17
0
Thank you very much my good man! This appears to be exactly the sort of thing I was looking for.