Negitive spike in circuit under no input condition

[prag.sinha]

Hi,

I was making a an op amp based circuit and came across a problem. I hope someone can help me.

The circuit consists of a transducer (Hall Sensor) with the output connected to an op amp buffer. This is followed by a RC high pass filter (~20Hz ) Low pass filter (~1KHz) to remove the DC bias and noise respectively. Next there is a non inverting op amp amplifier.

When there is input from the transducer, after the buffer, the DC bias and noise is removed and the sinusoidal signal is amplified. When there is no sensor input, only the DC level is supposed to be there, which gets removed. The problem is, when there is no input from transducer (ie only DC bias and no small signal sinusoidal), there is a negative spike of 3v at the output of the amplifier. This can cause error in the subsequent circuitry. The supply is +/- 5 v.

What can be the cause of this error and the remedy pls.



Thanks,
Pragati.

 

[udhay_cit]

Can you post your schematic. Whats the gain of the OPAMP?

 

[prag.sinha]

The gain is 147 (147k/1k). The ckt. is transducer generating mV sinusoidal o/p --> op amp buffer --> non inverting op amp stage. Most probably the problem that the amplifier is generating unbalanced output for balanced dual supply.