I am looking to build an absolute value circuit using a pair of op-amps, hopefully using a single supply and would like to simulate my design using TINA-TI.
The ultimate aim is to measure the voltage difference between an input and a reference voltage that is not necessarily ground. The modified LT1001 circuit in the answer to this question would be okay, but it is dual supply.
TI provide a useful application bulletin with various designs for absolute value circuits. Figure 5 in the application bulletin offers a nice single supply variant. I have reproduced it here in case of a stale link later.
I have entered the design into TINA-TI - I think without errors, but the simulation is not working with the output swinging immediately to mid-supply.
Why aren't I seeing the waveform as shown in the application bulletin?
Also at the bottom of the clip (below Figure 5.1) it contains the sentence "Notice that the input range of the circuit is 4V below the power supply rail.". What does this mean - the diagram shows the input to be -4V to +4V and the output 0 to 4V for a 5V supply?