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Clock Recovery Using Tuned Circuit

I am hoping to design a fairly simple clock recovery circuit using a Full Wave Rectifier, a tuned circuit and a Schmitt trigger. Currently, the system uses 4 level ASK signalling over a wireless channel model.

I am having trouble designing a full wave rectifier. I would like the circuit to be active and have come across a circuit which half wave rectifies, doubles this signal, and adds it to the original waveform. This may cause problems with component drift as the gain will need to be fairly exact. ANy other ideas?

Any possible circuit ideas would be greatly appreciated.

Reply to
stevieboy01
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Is the ASK four levels at the same phase, or are two states flipped?

John

Reply to
John Larkin

Sorry, didnt explain correctly. It doubles the amplitude of the half wave rectified circuit and then adds it to the non rectified signal. This is a fairly long-winded way of doing it, I admit, but is the only one I have come across.

Reply to
stevieboy01

It is 4 levels at the same phase. I want to use the diode square law to produce a squared version of the rectified signal and then filter the baseband signal out, using the tuned circuit or some other type of filter. Hopefully the clock will be derived from this.

Reply to
stevieboy01

Operating frequency?

"doubles this signal"?? Double the frequency or the amplitude?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

By the way, the bandwidth of the channel is approximately 15kHz

Reply to
stevieboy01

Then why not just bandpass filter at the carrier frequency (or equivalently, lock a PLL to it) and that's your recovered carrier. Then mix (ie, linear multiply) that with the incoming signal, lowpass, and that's your 4-level dibit data. I assume data and carrier are synchronous somehow.

Or even do a simple AM detector!

Why rectify? That's only needed if the data is biphase and has zero average carrier content, which would force you to look for the 2F thing.

What's the carrier frequency? Is it synchronous to the data?

This is potentially confusing to do in text. You could post a block diagram sketch to a.b.s.e. for discussion.

John

Reply to
John Larkin

This only works with a rail-rail op-amp, it won't be terrifically high-speed, the output impedance varies tremendously _and_ it's been ages since I've used one, but it does work:

___ .---|___|---------. | | | VCC | | + | | | | ___ | |\| | --------|___|---o----|-\ | | >----->|--o--o--------- .----|+/ | | |/| | | | .-. === === | | GND GND | | '-' | | === GND created by Andy´s ASCII-Circuit v1.24.140803 Beta

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On the negative half-wave the thing acts like a regular op-amp circuit, with the diode forward-drop being compensated for by the op-amp. On the forward half-wave the diode is reverse-biased and the signal just passes through the feedback network into the output (clever, huh?). You may want to buffer the output with a voltage follower to speed it up a bit.

--

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

Why not use a mixer chip like the NE612, or just use a windowed comparator since you were going to square it up with a schmitt trigger anyway?

--

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

You're going to do that at 433MHz?

Reply to
Fred Bloggs

The operating frequency will be approximately 20kHz

Reply to
stevieboy01

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