EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: elki on March 03, 2024, 10:04:33 am
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Hi everyone! Trying to simulate a basic transimpedance amplifier circuit with OPA656 using a single supply. In a dual supply configuration things work fine, but the single supply option does not seem to provide any working mode. Tried with other op amps with a similar conclusion. What could be wrong with the circuit below?
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Possibly you need an opamp with input rail-to-rail capability. You don't really need both rails, you need only 'ground capability'. Now you try to work with one input tied to ground but this exact opamp can't work like that.
You may try LM358, LM258 etc.
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Found ADA4625, which seems an ideal choice for transimpedance amplifier when working with single supply. However, still not getting the proper functioning.
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Most Analog Devices models have a demo/test schematic that comes with LTspice, provided by ADI, and guaranteed to work.
Start a new schematic, place only an ADA4625, then right click on the symbol and press the button Open this macromodel's test fixture. A complete schematic will open, with a test circuit for a photodiode amplifier. Use that as a starting point. Run it as it is, to check if it works on your install.
If it works, change the negative source V2 from -18V to 0V. With single supply it will take a little more to enter the normal working regime. Simulate 60us instead of only the first 6us. Then to remove the 2 at the end of the pulsed current source Id (so to generate a continuous train of pulses instead of only 2 pulses). You may want to limit the max time step to 1ns (now it is not specified) in case the time steps are not fine enough for 60us.
, so to make it single supply, and start tweaking from there.
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look at Net-Name carefully. you have "+10" and "+10V".
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Good catch!
look at Net-Name carefully. you have "+10" and "+10V".
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Thanks a lot - this is indeed a reassuring approach for not getting into trouble for missing some of the recommended settings.
Most Analog Devices models have a demo/test schematic that comes with LTspice, provided by ADI, and guaranteed to work.
Start a new schematic, place only an ADA4625, then right click on the symbol and press the button Open this macromodel's test fixture. A complete schematic will open, with a test circuit for a photodiode amplifier. Use that as a starting point. Run it as it is, to check if it works on your install.
If it works, change the negative source V2 from -18V to 0V. With single supply it will take a little more to enter the normal working regime. Simulate 60us instead of only the first 6us. Then to remove the 2 at the end of the pulsed current source Id (so to generate a continuous train of pulses instead of only 2 pulses). You may want to limit the max time step to 1ns (now it is not specified) in case the time steps are not fine enough for 60us.
, so to make it single supply, and start tweaking from there.