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Maxim Integrated - Integration Nation
Dennis Feucht

Z Meter on a Chip? Impedance Meter Phase Detectors

Dennis Feucht
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DaeJ
DaeJ
10/8/2013 8:32:37 PM
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Master
Phase detector
I wonder whether there is a calibration to get correct measurement in the circuit as shown in the BK 875A. In most case, device measurement tool would be adjusted every year based on warranty description.

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samicksha
samicksha
10/9/2013 2:30:05 AM
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Artist
Re: Phase detector
I am little confused, but please correct me if i am wrong, expression suggests a quadrature phase detector can be made by summing the outputs of two multipliers.

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D Feucht
D Feucht
10/9/2013 11:44:57 AM
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Blogger
Re: Phase detector
The B&K875A has a preponderance of trimpots - over 20 as I recall my count of them - and this is not unique to it. The ESI 253 has plenty of them too (only 10-turn pots instead). This ponderous amount of adjusting is caused by the lack of a uC in these products (too early) to do the calibrating. So yes, everything you can imagine that might need adjusting is included.


As for the two multipliers, the B&K875A had a clever phase detector that was full-wave: it used both half-cycles of the sine waveforms to contribute to the phase detector output. Each half-cycle was multiplied using an analog switch with either an in-line or quadrature reference sine from the generator. This scheme results in twice the PD gain of the more common half-wave design.

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Navelpluis
Navelpluis
10/10/2013 4:04:35 AM
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Artist
A couple of tips
Hi Dennis,

Great article, I love these kind of explorations into the Analog Domain ;-)

I have a couple of things to mention, but I am sure you already know them:

4046PLL is a beast. The phase comparator is excellent. But there is a little dead band in it, so Philips (now NxP) did a newer design, the 7046 to avoid this dead band

Further I found a mixer that is working from DC to 6GHZ with just 4 FET's inside. Basically this is for an analog frond end (of course) but I found out that for audio this one can be used as well. I build a chopper amplifier with it, gain of 50 and a 7nV/SQR(Hz) result, mainly due to this mixer. Normally this cannot be done with 'nuts and bolds' components and it should be integrated, nevertheless, it works fine here on my desk, as long as there is no wind blowing passby ;-)

These new parts with theur enormous nice specs can help you and also break your design in 2, but Analog folks like us will find their way around.

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D Feucht
D Feucht
10/27/2013 10:16:52 PM
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Blogger
Error Correction in Article
"Mistakes were made." Donald Rumsfeld, former Sec. of Defense, USA

In this article, it is stated that

"The B&K 875A has a full-wave phase detector that outputs twice the voltage..."

Also in one of my follow-up comments, I wrote

"This scheme results in twice the PD gain of the more common half-wave design...."

Don't believe this. It is true of peak detectors but not these phase detectors. The gain of the half-wave and full-wave synchronous detectors is the same. What is different is that the full-wave dectector outputs at twice the sample rate, not voltage. This has the advantage of making the low-pass filtering ripple less, or else the time constant less for the same ripple.

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etnapowers
etnapowers
11/26/2013 8:37:15 AM
User Rank
Master
Impedance diagram
In the impedance diagram of inductance/capacitance with series resistor is supposed that parallel capacitance is negligible?

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etnapowers
etnapowers
1/7/2014 3:56:31 AM
User Rank
Master
μController
To measure the phase angle by utilizing an high resolution μController is a good idea , provided that the bandwidth of the whole measurement system is enough to include the range of frequencies of interest.

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