[sdiy] LM13700 questions

[Stewart Pye]

On 8/17/2012 5:40 PM, Magnus Danielson wrote:
> On 08/17/2012 09:20 AM, Stewart Pye wrote:
>> Is it OK to use the current output of an LM13700 to feed the Iabc pin of
>> another LM1300?
>> According to the datasheet the maximum output current is in a suitable
>> range for the Iabc. The only concern I have is that the Iabc pin is
>> referenced to the negative rail.
>>
>> The application I have in mind is voltage control of modulation amount.
>> It seems silly to convert the current to a voltage and back to a current
>> again...
>
> You would be a diode away from the negative rail. Also consider that 
> the LM13700 output can be bi-polar where as the input only takes one 
> polarity. Voltage difference would come in the way.
>
> If you for some reason run into a problem (which I don't think if you 
> keep currents low enough) then using another current mirror at a more 
> moderate voltage would be a solution.
>
> Cheers,
> Magnus

As it will be within the circuit I'm designing, the non inverting input 
of the modulation amount VCA will only have positive voltages going to 
it (and the inverting input will be grounded), so the output current 
will only be positive.

Would it be wise to put a resistor between my mod amount VCA output and 
audio VCA Iabc input?

Regards,
Stewart.