>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 10 June 2005 14:18
>To: piclist@mit.edu
>Subject: Re: [EE] Analog "Proportional" Amplifier Design Question
>
>
>
>Todd Bailey wrote:
>>>Given Va, Vb, and Vc, with output Vout and single-rail supply Vdd: 
>>>Vout = [(Vb-Vc)/(Va-Vc)]*Vdd where Va > Vb > Vc, right?
>>
>>The equation you suggested is absolutely right.
>
>
>Thanks for all the replies!
>
>  Based on the above equation, as Spehro and others suggested, 
>I've been 
>drawing up a circuit using two diff amps to perform the two 
>subtractions 
>followed by an analog multiplier (the AD632 -- I'd used the 
>633 before and 
>thought THAT was an expensive IC) to divide the results of those two 
>operations.  I expect the final version will need a lot of trimming.
>  My next question is:
>  Is there a way to multiply the result of the division operation by a 
>constant (Vdd or some other scaling voltage) without another analog 
>multiplier?

Multiplication by a constant is simply gain, i.e. a classic inverting or non-inverting amplifier configuration.

Regards

Mike

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