Low-distortion Audio-range Oscillator

[thaumaturge]

Originally Posted by dirkwright

Does anyone have a source for a good surface mount to DIP adapter? I'm having trouble finding one.

In stock at Newark. TE conectivity (Formerly Augat / Thomas & Betts) Gold flashed berylium copper 4 point contact per pin.

808-AG12SM 8 pin
814-AG12SM 14 pin
816-AG11SM 16 pin.

Pricey at ~$5.72 ea. but the best I know of.
http://www.aboveboardelectronics.com...surf_800sm.pdf Spec sheet
Doc

[mickeymoose]

like that: SMD Adapters ? E

[dirkwright]

Thanks. I appreciate all the help.

[davada]

Originally Posted by dirkwright

Thanks. I appreciate all the help.

Also check Sparksfun they have a range of adapters for around 3-4 dollars.

David.

[thaumaturge]

I think I'm going the wrong direction here. My post covered Surface Mount PCB to DIP IC conversion.
Doc

[dirkwright]

Originally Posted by thaumaturge

I think I'm going the wrong direction here. My post covered Surface Mount PCB to DIP IC conversion.
Doc

I need to buy some 8 position SOIC to DIP adapters. I found a few in different places.

I have an idea for making a distortion analyzer. It's not an entirely new idea though. I'm still reading about different techniques for measuring distortion. My idea, which came to me out of the blue, is to use a differential amplifier with really high CMRR and extremely low distortion as a difference amplifier. The oscillator output goes to one input and the output from the device under test goes to the other input after going through an attenuator. The DUT has to be non-inverting for this to work, and the phase error has to be nill as well. Basically, if you feed a common mode signal to a differential amplifier, what's left at the output is the junk that's the difference.

The problem that I see with the typical notch filter type of distortion analyzer is that amplifiers under test don't just amplify and distort the fundamental frequency from the oscillator, they also amplifier and distort every harmonic that the oscillator produces, as well as the noise and IM products. So, the output of the DUT becomes a mess of harmonics, noise and IM products that you can't separate out with a notch filter.

Anyway, I'm still working with this idea and it's clear to me that in order for my device to work I need a very low distortion oscillator and a differential amp with crazy high CMRR and vanishingly low distortion. The LME49990 seems to fit the bill so far. CMRR is 137 dB and distortion is 0.00001%.

[dirkwright]

Since the + and - inputs, with feedback, have different impedance, something like this circuit has to be used for the distortion analyzer. It will magnify the difference signal (V2-V1) by 101 times.

[davada]

Originally Posted by dirkwright

I need to buy some 8 position SOIC to DIP adapters. I found a few in different places.

I have an idea for making a distortion analyzer. It's not an entirely new idea though. I'm still reading about different techniques for measuring distortion. My idea, which came to me out of the blue, is to use a differential amplifier with really high CMRR and extremely low distortion as a difference amplifier. The oscillator output goes to one input and the output from the device under test goes to the other input after going through an attenuator. The DUT has to be non-inverting for this to work, and the phase error has to be nill as well. Basically, if you feed a common mode signal to a differential amplifier, what's left at the output is the junk that's the difference.

The problem that I see with the typical notch filter type of distortion analyzer is that amplifiers under test don't just amplify and distort the fundamental frequency from the oscillator, they also amplifier and distort every harmonic that the oscillator produces, as well as the noise and IM products. So, the output of the DUT becomes a mess of harmonics, noise and IM products that you can't separate out with a notch filter.

Anyway, I'm still working with this idea and it's clear to me that in order for my device to work I need a very low distortion oscillator and a differential amp with crazy high CMRR and vanishingly low distortion. The LME49990 seems to fit the bill so far. CMRR is 137 dB and distortion is 0.00001%.

Hi dirkwright,

Not just the distortion but the noise as well. Generally the noise becomes the limiting factor with the notch method. But if you whan to analyze an oscillator one has to use a notch filter. The null method depends on having a DUT in the loop.

It's good to have both in the shop.

David.

[dirkwright]

Originally Posted by davada

Hi dirkwright,

Not just the distortion but the noise as well. Generally the noise becomes the limiting factor with the notch method. But if you whan to analyze an oscillator one has to use a notch filter. The null method depends on having a DUT in the loop.

It's good to have both in the shop.

David.

Yeah, I didn't think about how I was going to measure the distortion of the oscillator. I can't think of another way to do it right now without a notch filter.

[dirkwright]

Here's a twin T filter with adjustable Q. Input on the left, output to the right.