MF10 as a modulator filter

Hekko there.

MC1496 is an amplitude modulator chip and I use it to design a DSB modulator at 40khz carrier frequency. I decided to to convert my design to an SSB and filter one of sidebands(upper or lower sidebands, it's not matter which one) as my modulating signal has an almost 15khz bandwidth so what is your idea of using MF10 chip which is a Universal Monolithic Dual Switched Capacitor Filter?

Thanks in advance

The MC1496 is an analog multiplier; it's not an AM modulator chip per se.

In principal it should work. In practice -- maybe.

Plot the spectrum of the signal that you expect to come out of the 1496, then plot it as filtered by the MF10. See if it looks like it'll meet your spec. Then try it out....

Remember that switched-capacitor filters alias at the capacitor switching frequency, so you may wish to precede the MF10 with an anti-alias filter.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

et

.

Hi Thanks sir, ,Well I am a newbie in electronics filed What want to do is generatinf DSB by MC1496 and connecting its output to ONE MF10 to remove one sideband at 40khz of carrier frequency and amplify the last output by an OPAMP the modulating signal is sound which can be reach to 15khz max. Do you think one MF10 is enough to remove oneside band that has that bandwidth at that carrier freq?

As I know it is very hard to do so with an LC filter(much components and ..)

I don't think the MF10 is very suitable at 40kHz. If you don't want to go LC consider active filters with opamps.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

I've done this, and it worked extremely well--though not until I replaced the MF10 with an LMF100.

Cheers,

Phil Hobbs

Wow, didn't know they still made them. Yes, those can do 40kHz. Last time I used these in a design was in 1992 or so. They are so freaking expensive.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

3/DS010399.pdf

It seems to me you need to consider the lowest frequency to be sent to the modulator. For instance, if you sent 1Hz, then you would get

40001Hz and 39999Hz, which would be hard to separate. So the lowest frequency presented to the modulator determines the transition ratio of the filter.

While you think you can use either sideband, a low side mixer reverses the spectrum. To avoid this, use the lower side band.

I would use an off the shelf SCF rather than roll your own with a MF10. There are SCFs that emulate LC ladders. These filters have tighter specification than you would ever achieve cascading MF10 biquads.

If possible, have your SCF clock and modulator clock derived from the same source.

Have you considered a Hilbert transformer?

Hi, thanks,

what did you really? could you get a reasonable SSB signal?

what was the bandwidth of the wave which you wanted to remove? what about carrier freq? any schematics?

=AF=D9=86 =D9=85=D8=AA=D9=86 =D8=B9=D9=84=D8=A7=D9=85=D8=AA =D8=B2=D8=AF=D9= =87 -

=D9=82=D9=88=D9=84 =D8=B4=D8=AF=D9=87 -

the problem that I do not know if exists with this fliter chip is handelling that bandwidth just with one chip?! you guys do know that it is not easy to make a such filter using LC or RC circuits and it needs a lot of accurate resistors and capacitors. if you are thinking that ONE of these chips are working ok for this project maybe it uses anothe way to filter one sideband

/03/DS010399.pdf

Well, I have a 40khz carrier freq and an audio modulating signal which the freq is between 100hz to 15kh so i will have a 40khz carrier at the output of MC1496 and a 40khz -15khz and 40khz +15khz at either sidebandsas max and 40khz-100hz and40khz+100hz min Now I want to remove the lower or the upper sideband with MF10 and have an SSB signal at the output of MF10.

what thi smaeans: "While you think you can use either sideband, a low side mixer reverses the spectrum. To avoid this, use the lower side band"?

What is a SCF?

No amount of filtering will eliminate _all_ of the unwanted signals, so what you're really asking is "is one MF10 going to do an _adequate_ job".

Since you haven't defined what 'adequate' is, even in general terms (communications quality, high fidelity quality, crazy audiophile quality, cheap Chinese game quality, etc.), it's impossible to say even with extensive analysis if anything will meet your idea of 'adequate'.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

for one, that's a Double balanced mixer chip

and to make it easy on you , a selectable latter filter would most likely do you well.

That brings some old days back! :)

"

Filter?

You may have better luck with one of the newer parts. You want a high Q up at 40KHz so you need a lot of gain bandwidth product to do it.

You can also get much better non-universal filters. It may be better if you can find one that you can get to do what you want.

^^^^^^^

How did you make these characters?

It depends on the shape factor you want. Considering the LMF100 contains only two such filters it won't that great. This app note may help:

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

That's about when I did it too.

Cheers,

Phil Hobbs

I'll have to go look...it was at least 15 years ago, and maybe more. I was building a crossed-beam laser particle counter using an 80-MHz acousto-optic cell, and wanted to get rid of the noise at the image frequency--a 3 dB sensitivity improvement. Since the frequency shift was small, about 0.1% of the centre frequency, a SSB mixer was easier than filtering. I could have done a double conversion, of course, but I'd never built a phasing SSB mixer, and the LMF100 is quite good at low-Q all-pass networks, so I built the

90-degree phase shift network (aka Hilbert transform filter) using one of those.

Cheers,

Phil Hobbs

01/03/DS010399.pdf

SCF stands for Switched Capacitor Filter.

Say you want to keep the lower side band. We have now established the lowest frequency in the baseband is 100Hz. Your filter must pass

39900Hz and reject 40100 Hz., assuming no carrier leak. That implies a transition ratio of 1.005. You will not do this with the MF10. You need a ladder filter. Even then, something like a Max294 has a 1.2 transition ratio.

Have you considered a Hilbert transformer? A Hilbert transformer and a more complicated mixer will reduce the requirements needed for out of band rejection.

Maybe you take the wrong approach.

The Weaver SSB modulator [1] directly creates SSB without too much filtering problems. I once did a design for that to create speech SSB for amateur radio, published in the Dutch Veron magazine and later in AFAIR Wireless World. It worked without any critical filter tuning. Never build it myself, just had the idea, others build it and it was OK.

It used 4x TBA120 as mixers (carrier signals send through the IF inputs, analog to the multipliers), 2x SN7474 for the audio and RF quadrature signal generation and a simple PI-filter between the mixers. Output was directly in the 3.5 or 7MHz band.

Arie de Muynck

[1]

ing

f,

nal

in

Anything that generates less of the unwanted sideband is the way to go. You will probably still need to so some filtering, but the out of band rejection requirements are reduced if you produce less in the first place.