🚀 go-pugleaf

Kong Kritayakirana (kong@leland.Stanford.EDU) wrote:

: 1. I don't need an opamp with awesome slew rate to make an integrator, right?

That's not so easy! The large-signal-bandwidth is given by maximum output-
voltageswing and the slew-rate. So, you must know the maximum outputfre-
quency the integrator must work with which amplitude.

Formula:	dU out  |
		------  |     =   2 * PI * f * Upeak out
	  	  dt    |max  

The opamp internal slew-rate must be higher than the slew-rate given by
your integrator! That's important for precission. If you want a highprecis-
sion integrator for dymamics you should take an opamp with a slew-rate
what is 10 times faster than the "slew-rate" of your integrator.



: 2. How do I deal with Voffset problem.

If the opamp has no offsetcompensation-inputs, you must use the noninverting-
input of the opamp. The deviation of this input from ground compensate the
the offsetvoltage. You can make the offsetcompensation adjustable by a pot-
meter with low voltagerange.



: 3. This is going to be used in a high precision, low noise data acquisition.
:    The professor I work for doesn't know anything about electronics, but he
:    WANTS LOWEST POSSIBLE noise. What opamp should I use for Vinput with band
:    width of about 500kHz. The circuit is NOT a power circuit.

For very less noise:	It's dependet from sourceimpedance and the used
			opamp. For high-imp. it's better opamp with fet-
			input-stage, for low-imp. take such with bipolar
			pnp-input-stage. The first case, it dominate the
			input-voltage-noise and in the second case it domi-
			nate the input-current-noise which generate a vol-
			tage-noise in the source-impedance. 

Back to the slew-rate:	With a sinus-frequency of 500 kHz and a output-
			voltage-swing of 10 V peak you must take a opamp
			with 30 Volt per microsecond or more. And don't
			forget you first question. Now you can give the 
			answer of your question. You need really a fast 
			opamp!


So I hope I can help you. But I think the better way for you is to learn
about this stuff from good electronics-book.

Bye Thomas