[sdiy] Bending a Sum

[Tom Bugs]

OK - http://bugbrand.co.uk/images/sumbend2.jpg

You can see that this is stolen from the linearization idea - quite 
possibly I'm doing DUMB things. (I was never very good with transistors..)
But you can see here (from red-* node) the voltage from 0V to -700mV

I did try messing around from here, but didn't arrive at anything as yet..

Cheers, Tom

On 18/11/2013 18:59, Tom Bugs wrote:
> Cheers Tom.
>
> I've only really had a bit of a play in LTSpice (which I'm not fluent 
> in!) partly because I'm mainly away from my workshop at the moment.
> Interestingly, I did think maybe transistors could somehow be used..
> I arrived at something simple with a PNP that gave quite a similar 
> shape, but was between 0V and about -0.7 (instead of +5V to 0V) and, 
> without adding further opamp buffers, it didn't seem like I could 
> shift it up and scale it.
> Ha, I'm probably being overly stingey - but I have a basic proto I'm 
> playing with (which has the posted simple summer) which has a very 
> tight PCB so I'm loathe to rip it all up if there's a simple solution 
> not too far away. [reason for change - exponential response isn't 
> ideal...]
>
> Maybe I'll sketch the PNP idea and see if that gives any further ideas.
>
> Ta,Tom
>
>
> On 18/11/2013 17:12, Tom Wiltshire wrote:
>> Hi Tom,
>>
>> If the blue line was the other way up, it'd be a soft-knee 
>> compression curve, or a soft distortion. Perhaps you could experiment 
>> with some of the typical soft distortion circuits, and then invert 
>> the output to get their output to apparently clip heading towards 
>> zero volts instead of towards 5V. Alternatively use the soft clipping 
>> on the negative half of the waveform and then shift it up I suppose.
>>
>> I've only tried straightening out the 2164 in software myself, so 
>> these ideas are untested.
>>
>> HTH,
>> Tom
>>
>> On 18 Nov 2013, at 13:29, Tom Bugs <admin at bugbrand.co.uk> wrote:
>>
>>> Just wondered if anyone may have a brainwave on this little problem...
>>>
>>> It is around the area of linearizing the response of an SSM2164 - 
>>> but, at the moment (blah blah) I wanted to see if I can achieve a 
>>> rough linearization WITHOUT using the well documented Irwin EDM 
>>> technique.
>>>
>>> http://bugbrand.co.uk/images/SumBend.jpg
>>>
>>> I just have a simple opamp sum stage to generate 5V to 0V from a 0V 
>>> to 10V control - that's the green line.
>>> The standard linearization technique achieves the blue line.
>>> How could I bend green to blue without too much extra complexity 
>>> and, crucially, without using another 2164 cell?
>>>
>>> Thanks!Tom
>>>
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