Simple Instrumenatation Amplifier Circuit
I'm trying to debug a larger circuit of mine by breaking it up into smaller parts and dealing with them one by one. One of the parts of the circuit is an instrumentation amplifier.
The chip is using is the INA118 for TI (datasheet #-Link-Snipped-#).
The pin-out of the chip is shown here:-
![[IMG]](proxy.php?image=http%3A%2F%2Fimg4.imageshack.us%2Fimg4%2F452%2Finadata.png&hash=c34c9be1396070cc956fdf3a584eb195)
The chip is capable of operating with a single supply, or at least that's what the datsheet has led me to believe. However, to this point I have only been able to get it to do anything meaningful when I use a dual supply of +/- 2.5V. At the moment I'm trying to get it to work witha single supply of +5V & 0V and I'm having no luck at all.
The setup i have at the moment is as follows:-
Pin 1: Connected through two 40kOhm resistors in series to pin 8. Sets the amplifier gain.
Pin 2: Connected through a 390kohm resistor. This is the inverting input pin.
Pin 3: Connected through a 390kohm resistor. This is the non-inverting input pin.
Pin 4: Connected to the negative port of the power supply to give -Vcc = 0V.
Pin 5: Grounded to give 0V offset.
Pin 6: Output.
Pin 7: Connected to the positive port of the power supply to give +Vcc = 5V.
Pin 8: Connected through two 40kOhm resistors in series to pin 1. Sets the amplifier gain.
Using a probe (with the negative end connected to the negative power supply port) I've checked and found that Pins 4 & 7 are at 0V and 5V respectively as desired. Pin 5 is at 0V as desired. Pins 2 & 3 for some reason show a voltage of around 0.48V that I don't know the reason for. Finally, pins 1 & 8 each show a voltage of around 3.5V which i also am not sure is desirable.
I've tried grounding one of the inputs and connecting the other to both a small DC (~20mV)voltage and also to a small amplitude (~20mV p-p) sine wave. In each case I failed to see the expected, amplified and uninverted, output signal.
Can anybody see any issues with how I'm supplying power to my chip? Or any other issue that might be causing my problem?
Thanks...
The chip is using is the INA118 for TI (datasheet #-Link-Snipped-#).
The pin-out of the chip is shown here:-
The chip is capable of operating with a single supply, or at least that's what the datsheet has led me to believe. However, to this point I have only been able to get it to do anything meaningful when I use a dual supply of +/- 2.5V. At the moment I'm trying to get it to work witha single supply of +5V & 0V and I'm having no luck at all.
The setup i have at the moment is as follows:-
Pin 1: Connected through two 40kOhm resistors in series to pin 8. Sets the amplifier gain.
Pin 2: Connected through a 390kohm resistor. This is the inverting input pin.
Pin 3: Connected through a 390kohm resistor. This is the non-inverting input pin.
Pin 4: Connected to the negative port of the power supply to give -Vcc = 0V.
Pin 5: Grounded to give 0V offset.
Pin 6: Output.
Pin 7: Connected to the positive port of the power supply to give +Vcc = 5V.
Pin 8: Connected through two 40kOhm resistors in series to pin 1. Sets the amplifier gain.
Using a probe (with the negative end connected to the negative power supply port) I've checked and found that Pins 4 & 7 are at 0V and 5V respectively as desired. Pin 5 is at 0V as desired. Pins 2 & 3 for some reason show a voltage of around 0.48V that I don't know the reason for. Finally, pins 1 & 8 each show a voltage of around 3.5V which i also am not sure is desirable.
I've tried grounding one of the inputs and connecting the other to both a small DC (~20mV)voltage and also to a small amplitude (~20mV p-p) sine wave. In each case I failed to see the expected, amplified and uninverted, output signal.
Can anybody see any issues with how I'm supplying power to my chip? Or any other issue that might be causing my problem?
Thanks...
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