[sdiy] Blackmer cell

[Ian Fritz]

Interesting.  I hadn't learned about the Blackmer cell before.  I notice 
that if you remove the PNP's (Q3 and Q4), the I_CC and the V_B sources, 
then it's just our usual current-sink expo converter.  Similarly, removing 
the NPN's gives the current-source one.

At 09:10 AM 12/6/05, James Patchell wrote:
>A few years back, I experimented with this type of VCA (using a THAT140 
>for the transistors)...and for some odd reason, which I can't remember, I 
>decided not to use it for the application I was doing.  It is a fairly 
>simple VCA to build.  You will find a complete circuit for it in the LM194 
>data sheet.  This is what I built up, but like I said, I used the THAT140 
>instead of the LM194/2n3810 transistor pairs shown there.
>
>At 02:35 AM 12/6/2005 -0500, Aaron Lanterman wrote:
>
>>On Mon, 5 Dec 2005, JH. wrote:
>>
>>>It's a Blackmer cell. No offset to speak of (compared to OTAs),
>>>but needs a servo configuration which probably limits its speed.
>>
>>I hadn't encountered the term "Blackmer cell" previously.
>>
>>In playing with VCA designs, is it worth experimenting with building some 
>>discrete Blackmer cells?
>>
>>See http://www.edn.com/article/CA236413.html, Figure 3...
>>
>>http://www.edn.com/contents/images/236413.pdf
>>
>>- Aaron
>>
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>>
>>Dr. Aaron Lanterman, Asst. Prof.       Voice:  404-385-2548
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>
>         -Jim
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