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You might notice that many of my writings start with “Back in the day”. Not wanting to disappoint I will say that back in the day we used to use wire wrap technology when we needed a somewhat solid, somewhat reliably assembly. Given a readable schematic a good tech could return a working or near-working unit in a day or two depending on the completeness and accuracy of the schematic.
A great tech not on OP Amps driving capacitance. http://www.analog.com/library/analogDialogue/archives/31-2/appleng.html
Q. How does capacitive loading affect op amp performance?
A. To put it simply, it can turn your amplifier into an oscillator. Here's how:
Op amps have an inherent output resistance, Ro, which, in conjunction with a capacitive load, forms an additional pole in the amplifier's transfer function. As the Bode plot shows, at each pole the amplitude slope becomes more negative by 20 dB/ decade. Notice how each pole adds as much as -90° of phase shift. We can view instability from either of two perspectives. Looking at amplitude response on the log plot,circuit instability occurs when the sum of open-loop gain and feedback attenuation is greater than unity. Similarly, looking at phase response, an op amp will tend to oscillate at a frequency where loop phase shift exceeds -180°, if this frequency is below the closed-loop bandwidth. The closed-loop bandwidth of a voltage-feedback op amp circuit is equal to the op amp's bandwidth product (GBP, or unity-gain frequency), divided by the circuit's closed loop gain (ACL).
I will be doing a workshop this Friday at VCF East on computer architecture. Each year is bigger and better and this is the second year for three days of computer related festivities. Worth the drive if you are in the NJ, NY, PA area!
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