exponential converter current source

Sat, Apr 9, 2011

I reversed the current direction by using PNP transistors instead of NPN transistors (plus some other minor alterations). I also realized that the output current of the expo conv in the previous post (7mA) was way too high for the LM13700 (max current 1mA) so I adjusted the resistor in the iref connection to 10 megaohms! Max output to the LM13700 is now 705µA.

The schematic:

plot (current source leads to negative figures in LTspice)

calculations:

So expo out is at max 705µA and at min 32nA. On to the actual filter!