Hello. I'm having trouble to figure out why my calculations don't match the measurements when I hook up a LM13700 as Voltage controlled resistor.
Similar issue for both configurations: single ended or floating.
as for LM13700 Datasheet (fig.28, Floating Voltage-Controlled Resistor)
THEORY:
the formula given is Rx= (2 * R)/(gm * RA) , where gm is 19.2 * Ibias
In my calculations,
Ibias is max 0.42 mA
Ra is 1K
R is 100K
The Rx resulting should be 24.8 K and for descreasing Ibias, Rx goes up.
PRACTICE on breadboard:
following the circuit , i feed max 0.42 mA at Pin 1 and 16 of the LM13700 and i set up a simple voltage divider to test it in practice as follows.
Vin is 5.19 V, R1 is replaced with the LM13700 and r2 is 100k.
Following the theoric calculations, i should expect Vout =4.16.
But what i can measure in practice is 3.36V though.
Do you have any suspects or hints to give?
I take for granted that Ibias of 0.42 mA that i split between pin 1 and 16 of the OTA, has to be used as it is in the Formula ( and so i don't have to use 0.42mA/2)
Thanks a lot for any advice or help.
Similar issue for both configurations: single ended or floating.
as for LM13700 Datasheet (fig.28, Floating Voltage-Controlled Resistor)
THEORY:
the formula given is Rx= (2 * R)/(gm * RA) , where gm is 19.2 * Ibias
In my calculations,
Ibias is max 0.42 mA
Ra is 1K
R is 100K
The Rx resulting should be 24.8 K and for descreasing Ibias, Rx goes up.
PRACTICE on breadboard:
following the circuit , i feed max 0.42 mA at Pin 1 and 16 of the LM13700 and i set up a simple voltage divider to test it in practice as follows.
Vin is 5.19 V, R1 is replaced with the LM13700 and r2 is 100k.
Following the theoric calculations, i should expect Vout =4.16.
But what i can measure in practice is 3.36V though.
Do you have any suspects or hints to give?
I take for granted that Ibias of 0.42 mA that i split between pin 1 and 16 of the OTA, has to be used as it is in the Formula ( and so i don't have to use 0.42mA/2)
Thanks a lot for any advice or help.
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