Fun And Games With Spice

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Mike H
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#91

Post by Mike H »

I thought of something of the sort, but wasn't overly convinced
 
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#92

Post by Mike H »

Slight detour ~ the standard LTspice generic simple op-amp model. Slight problem in that the output is fixedly referenced to ground (node 0)
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Simple Op-amp model
Simple Op-amp model
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The simple op-amp symbol
The simple op-amp symbol
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Mike H
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#93

Post by Mike H »

No, it doesn't make any difference where the bottom of the G element is connected! Still works even if + input is DC offset
 
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#94

Post by Mike H »

Might have something going now chaps, more info later

10M45S I'm talking about
 
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#95

Post by Mike H »

Oh alright then here's a quick picture :D

Tried to get the dynamic impedance at 160k or near enough according to data sheet (@ 300R bias, 10mA), hence the slopes. Which we actually want else it won't work as a load

Resistance steps 30 - 3300R by octaves
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Nick
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#96

Post by Nick »

Looks good, the only unknown is the AC behavior.
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#97

Post by Mike H »

There is that minor detail yes. :D
 
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#98

Post by Mike H »

Basic block diagram, doesn't actually look like this but this is the prinicple
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#99

Post by Mike H »

It do am ack-cherley looks like this:
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#100

Post by Mike H »

Test #1 ~ 6SL7

DC = 1.4mA.

Using another 6SL7 for the CCS, gain is 43 plus some fraction.

Using 10M45S model, gain is 60.5.

The dynamic resistance is Volts change divided by current change is that right?

If so I make it a shade over 320k
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#101

Post by Mike H »

Edited

Using the 6SL7 CCS, the positive tips of the waveform were begining to round off very slightly. With this they don't:
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Last edited by Mike H on Wed Apr 28, 2010 3:52 pm, edited 1 time in total.
 
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Nick
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#102

Post by Nick »

The dynamic resistance is Volts change divided by current change is that right?

If so I make it a shade over 320k
Are you measuring this with the 470k resistor in parallel with the CCS?
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#103

Post by Mike H »

Test #2 ~ 1kHz square wave, 1uS rise and fall times.


The spikes at the bottom are something to do with the input not the output. :?:
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#104

Post by Mike H »

Nick wrote:Are you measuring this with the 470k resistor in parallel with the CCS?
Since you mention it yes. :oops: So probably considerably more, data sheet does say can be up to 900k
 
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Mike H
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#105

Post by Mike H »

Test #3 ~ source follower output

Gain is up to 66.66, and maintains it into a 100k load on the output.
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