hello every one. i am ejaz. i am designing a project that needs multiplication of two ac signals and i don't know how to do this.plz help me on u04f061@yahoo.com
if u can. i shall be very thankful for that person who will solve my problem.
i hava problem of jaust multiplication of two ac voltage signals ie sin(wt)*sin(wt)

 

Originally posted by u04f061@Jan 3 2006, 11:15 AM
hello every one. i am ejaz. i am designing a project that needs multiplication of two ac signals and i don't know how to do this.plz help me on u04f061@yahoo.com
if u can. i shall be very thankful for that person who will solve my problem.
i hava problem of jaust multiplication of two ac voltage signals ie sin(wt)*sin(wt)

[post=12860]Quoted post[/post]​

There are many approaches to perform analogue multiplication. The easiest way is to use an analogue multiplier IC (have a look at Analog Device or Burr-Brown (TI) multiplier ranges). These ICs are quite expensive, except one from AD which is cheaper than the other.

If you want to design your own multiplier, then the easiest approach is to use two logarithmic amps and then adding the results together with a summer and then reversing the signal back from log. Log amp is not that difficult to realise, you could search for these on the internet. It would be cheaper, but the result might not be that good (it depends largely on your design skill).

Another possibility is to consider amplitude modulation circuits. These basically perform signal multiplication, although the result might not be absolute. If you do not require absolute result then this might be the easiest option.

Other multipliers exist, but these are application specific, such as heat resistors and thermocouples for RMS measurements (slow, needs temp compensation but good at averaging) and I've seen one design involving VCO.

 

I agree with n9352527. Your best bet is to use an analog multiplier. The Motorola device whose datasheet is linked to below will give you a feel for what you might be up against if you decide to tackle the problem at the device level. You did not mention the frequency of the two sinewaves you wish to multiply together. The motorola device is good up to several megahertz. You will also need a fairly good opamp to go with the analog multiplier. This will be particularly true if your frequencies are in the megahertz range.

Here is a link to a Four quadrant multiplier IC (part number MC1495) manufactured by Motorola. The datasheet has a pretty good description of how the device operates.

hgmjr

 

Originally posted by u04f061@Jan 3 2006, 02:15 PM
hello every one. i am ejaz. i am designing a project that needs multiplication of two ac signals and i don't know how to do this.plz help me on u04f061@yahoo.com
if u can. i shall be very thankful for that person who will solve my problem.
i hava problem of jaust multiplication of two ac voltage signals ie sin(wt)*sin(wt)

[post=12860]Quoted post[/post]​

Dear ejaz

Multiplying two sinusiodal signals results in frequency shifting. this is so commonly used in Amplitude Modulation in communcation engineering. The analog electronic device that is used to do this task is called "mixer". the mixer circuit consists of a network of MOS transistors that are followed by an operational amplifier with two outputs positive and negative. Unfortunately, I don't have the circuit diagram but I'll send it to you once I get it.

Yours faithfully

 

Here is another device from Motorola that implements the product of two signals.

http://www.onsemi.com/pub/Collateral/MC1496-D.PDF

Unlike the MC1495, the MC1496 is not obsolete.

hgmjr

 

first of all i am thankful to all those who replied to this topic.now the idea of analogue multiplication is clear to me.my project requires the integration result obtained by multiplication of two signals over only one cycle and for all other cycles the result of first cycle should be displayed on CRO.ie it integrates the function using integrator op-amp circuit and then stores this result and displays this untill the supply is shut down .digital data is stored easily using any type of digital storage device but i want to store this analogue data.is it possible to store analogue data without converting it into digital data. if it is plz reply.
i shall be very thankful to all those who will try to help me.

good bye
ejaz ahmed