Sine to square wave conversion

You don't NEED a band-pass filter, because you are trying to eliminate only frequencies higher than the one you want. So a high-Q low-pass filter, peaked at 1 kHz, would be good. That gives you 'gain' at the frequency you want, while it attenuates the harmonics in proportion to their order.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Hello Jim,

Why would you want to vary the excitation frequency on a sonar (the civilian versions, of course)? If it was a long range job where return signals become mushy in the distance you'd need a tracking filter that keeps the low pass limit constant but reduces the high cut-off with depth.

Regards, Joerg

Hello John,

That would be like debating whether a seal is more of a land animal or a sea animal ;-)

Regards, Joerg

Hello Jim,

Understandable. It's good that you have competent folks on the other side. Makes projects more fun.

Regards, Joerg

Simple arrangement may give food for thought. Circuit gives about 5V sinewave out for a 5V squarewave in. Sine distortion about 0.2%. Essentially it's just a tweaked low pass filter.

6dB, 1kHz peaked, 3rd order Cheb', with added 3kHz notch (zero) to kill the square wave big third harmonic. Q of about 5 dissuades circuit from getting toooo sniffy about component tolerances. As the frequency is so low then most opamps are OK to use.

The circuit needs viewing in a fixed space font, such as Courier 390n || .-----||-----o----------. | || | | | | |\\| | | '----|-\\ | ___ ___ | ___ | >--o-o OUT o -|___|---o---|___|---o---|___|----o----|+/ IN 6k8 | 10k 10k | |/| | || | o-----------||-----------o | || | | 68p | --- --- --- 100n --- 560p | | GND GND

(created by AACircuit v1.28 beta 10/06/04

But it's Sallen-Key, which will be a bitch to tune accurately.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

One of my first assignments at Motorola, some 43 years ago, was to analyse the various configurations for active filters and study the component sensitivities.

Sallen-Key has sensitivities that vary as "Q".

Huelsman configurations just move the sensitivities to other places in the circuit... made him mad as hell when I pointed that out to him in front of an audience at Motorola ;-)

State variable and variations are pretty good.

My gyrator configuration takes more parts but has component sensitivities of 0.5 to 1.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

S-Ks are fine for anti-aliasing, deglitching, 2 or 3-pole things like that. They make excellent Bessels, since Qs are low. I've even done them in software.

John

Mark IS the client ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Yes indeed!. As once found to my cost, they're twats if used in production. In this case the sensitivities mainly translate into variations in the sine THD figure. Sandeep hadn't mentioned this so the circuit can be used as a good starter-for-ten with a low component count. regards john

I'm not sure about that... particularly "better than a 10-pole lowpass".

What I did try was this...

2nd order Butterworth low pass filter, corner at 1KHz, and a 2nd order band pass filter, center frequency of 1KHz, with "Q"

Result, BP wins until f = Q x 1KHz, then LP is better.

Caught me by surprise, I thought the BP would always be better.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

What "-prog-" are you using?

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Can you name a PLL with a sine-wave VCO? I have not seen one.

McC

Expensive! Do you know anything about a program called "Elsie" ?

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Worth printing and saving. How did you design in the 3 kHz notch?

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Ask me about my work with TOW missiles some time ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Compact high-end (>$100k) civilian sonar systems are capable of operating on different frequency bands. It's a range/resolution issue. These sorts of systems are also used in semi-disposable (there is a chance of it getting blown to bits) military systems for search and classification. Lower freqs for search, higher freqs for classification.

--
Mark

Hello Mark,

Sure, medical ultrasound systems do the same thing. 7.5MHz-12MHz to scan the carotid arteries and 3.5MHz at the other end of the scale to check for a possible aneurysm case deep down where the aorta is. But that doesn't require tracking filters, it is simply switched by the operator (and in med ultrasound usually accompanied by a transducer change). Tracking filters are used for varying the bandwidth on the fly while receiving a train of echoes. This is to exclude higher frequency spectrum where there will more the noise the deeper the echoes come from. So they scoot the upper slope of a bandpass downwards.

Regards, Joerg

selection.

"Design"?. Gerroutofere. Just click the "add stop band zeroes" button!. The -prog- then modifies the prototype Chebyshev polynomials and adds a term to the transfer function. Results in the small 68pF cap (ideal resonance value is 73pF). Took about 5 minutes to 'design' the filter. Biggest time was spent in playing with the complex poles to confirm I had a useful initial response, given the 3rd order setup. For me, the magnificent luxury of these kind of programs is that once a particular layout has been decided, passive, active, or digital solutions are just a click away. For example, the sine filter here can instantly be implemented as a (say) FIR, 100 tap, Blackman-Harris type or 'step invariant' IIR. Task schedulers?, office assistants?, pah, what fun are they :-). regards john