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dac I/V convertion with very low distortion
dac I/V convertion with very low distortion
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Old 18th August 2012, 09:11 AM   #241
Shinja is offline Shinja  Japan
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I understood the "base current" of driver transistor swing due to the current swing of 5k ohm resistor.
I misunderstood again ,sorry.
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Old 18th August 2012, 10:31 AM   #242
Shinja is offline Shinja  Japan
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not so good...
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Old 18th August 2012, 12:50 PM   #243
smms73 is online now smms73  Portugal
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Quote:
Originally Posted by Joachim Gerhard View Post
Yes, the circuit i build makes some trouble. I have one or two ideas to try though.
I will publish what i have at the moment. Maybe somebody has an idea how it can be made to work.
Joachim,
maybe the problem is the dc offset , try connect 2 batteries like this image.
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Old 18th August 2012, 12:58 PM   #244
smms73 is online now smms73  Portugal
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Quote:
Originally Posted by Shinja View Post
not so good...
I think Q3 and Q2 have very low Vce
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Old 18th August 2012, 01:21 PM   #245
Joachim Gerhard is offline Joachim Gerhard  Germany
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I will try post post 243.
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Old 18th August 2012, 02:15 PM   #246
dirkwright is offline dirkwright  United States
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This one sim's with THD of 0.0007%. S/N is 135dB. Just a tweek here and a tweek there. No big deal. 1mA in and 1.41Vrms out.
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Old 18th August 2012, 02:39 PM   #247
Joachim Gerhard is offline Joachim Gerhard  Germany
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I wonder why my build did not work so far. I use different resistors from dirk but it is basically the same. i will do some research soon.
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Old 18th August 2012, 03:28 PM   #248
Joachim Gerhard is offline Joachim Gerhard  Germany
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I tried the version with the two batteries. Again no luck. What i can see is oszillation.
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Old 18th August 2012, 04:27 PM   #249
tankcircuitnoise is offline tankcircuitnoise
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And 1 nanosecond edges will upset operating conditions.

The nonlinearity of bipolars (I do like bipolars, carefully used),

Ie Delta_Vbe
1mA -------
2.718mA +0.026 volt
1/2.718mA -0.026 volt

may show the distortion issue. Boosting Vbe by .026v will almost triple Ie.
Reducing Vbe by .025v reduces Ie by approx 70%.

That is
1mA--baseline bias
2.718mA at +26mv
0.39mA at -26mV

That's a big positive response, versus weak negative response.
Lots of 2nd harmonic.

tank
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Old 18th August 2012, 05:05 PM   #250
Joachim Gerhard is offline Joachim Gerhard  Germany
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I will try a bandwidth limiting.
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