Original question:
while doing the circuit,how can we provide the reference current to the log amplifier.can u share any design for reference of log112
Hello Aftab,
The LOG112 IREF current is easily set. IREF is simply the ratio of VREF/RREF. Since VREF is 2.5 V, and if RREF is a 1 Megohm resistor, they would result in an IREF of 2.5 uA.
The illustration below may make the reference circuit more evident. In it I2 is selected to be IREF and equal to VREF/RREF. I1 and I2 would be entered into the VLOGOUT equation shown below to determine the voltage at that point in the circuit.
Regards, Thomas
Precision Amplifiers Applications Engineering
Hi Thomas,
I need 1 uA current to the I2 as reference current,So i selected the Rref as 2.5MEG, But while testing in TINA the current as Iref is not showing as 1uA And the i tested with 1 MEG But the current showing is same.
Hello Aftab,
I see that TINA TI does not include the LOG112 in the Spice Macros menu. So you must have had to construct it from the Spice listing provided on the LOG112 web page. Something may not be connected correctly in your circuit.
I am providing you with a TINA LOG112 model that I use. It provides the correct reference current. You can see some results I obtained simulating with it in the screenshot below.
Here is my LOG112 TINA file:
This LOG112 model provide correct reference current and performance.
Regards, Thomas
Precision Amplifiers Applications Engineering
