# Best way to generate 4th power for signal ?

• posted

Could some electronics guru please provide some feedback on this issue ? I want to generate the 4th power of a given signal. The design I had in mind was to have two mixers running in parallel, where both inputs to each of the mixers would be the signal whose

4th power is to be generated. The output of each is a the square of the original signal. These two outputs are input for a third mixer, whose output is the 4th power of the original input signal. Are there any better/simpler solutions ? Any hints/suggestions would be valuable. Thanks in advance.
• posted

Someone else will step in and do all this with A/D and D/A converters and a tiny microcontroller :-).

If the input is only ever positive in the scale you choose it can be done a little simpler. A logarithm circuit followed by a scale-by-4 circuit followed by an antilog will be much easier. Scale by 4 can be just the feedback network around the individual log or antilog. See

_output and note that what they call "Exponential Output" in the next section is what I call an "antilog". Zero-setting becomes critical.

Tim.

• posted

You need to provide the type of signal you are dealing with?

Digital pulse ?

Analog Sine wave?

what frequency you are working with ?

etc.

There are answers, how ever, with out more details, I don't think you'll like the pile of them coming at you.

For example, If I was to deal with something in the R.F. range, I could create a band pass amp designed for the 4th tone and force a harmonic of that signal to be created and amplified..

But you don't supply the freq and it's range nor, the type of signal.

You also have PLL (Phase Lock Loop) options.. etc.

Jamie

• posted

Fourth power anything would tend to have dynamic range limitations.

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Many thanks,

Don Lancaster                          voice phone: (928)428-4073```
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I'm guessing by 4th power he means 4th harmonic? Here's a circuit for odd harmonics. Can someone give me a simple explanation why you can't get even harmonics from it.

Mikek

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Ahh.. Fourier of squarewave only has odd harmonics. Hmm any way you can create sawtooth to do this. Mikek

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It seems to be a square wave generator ( a diode clipper) feeding a filter. Square waves are composed of odd harmonics.

"In contrast to the sawtooth wave, which contains all integer harmonics, the square wave contains only odd integer harmonics."

-- Les Cargill

• posted

Ok, since we're on this subject..

use two of those as a passive circuit with enough signal level, and you have your x4 signal.. no harmonics to deal with.. Well, not directly any how :)

Jamie

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Well, Tim S. mentioned digital and log-antilog. There are analog multipliers, it'd be nice if you gave some frequency range. above or below 10MHz. say? Do you need amplifiers after your first pair of mixers? (I've never used mixers as squarers, only as frequency 'shifters'.)

Can you tell us why you want to measure the fourth power of something?

George H.

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Analog multiplier, View in fixed pitch font:

a^0            A^2          A^4```
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Don't you mean two mixers in series? Gilbert cell mixers are good multipliers for a limited dynamic range (5 mV to 100 mV). Logarithm converters are better for dynamic range, IF your signal doesn't get near zero (the logarithm converter has a deficiency when it renders negative infinity, the logarithm of zero).

• posted

Costas loop.

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Tim Wescott
Wescott Design Services```
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Yes, or full-wave rectify, filter at 2 fc, rectify again, and finally filter at 4 fc.

But a Costas loop works better.

Jeroen Belleman

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What input voltage do jou have? If it is max 5 volt, the output will be 625 volts. If the input is 0.5 volt, the output voltage willbe 0.0625 volt.

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pim.```
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Probably homework.

Cheers! Rich

• posted

Not relevant. This guy wants to understand how to demodulate a QPSK signal.

Jeroen Belleman

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