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Showing posts from November, 2016

An Amateur’s View on the P2: Slew Rate and the Oscillator [Part 2]

In part 1, the basics of the P2 have been discussed through easy straightforward simulations in LTSPice. In this article, we delve further into the P2’s design. It hasn’t been easy investigating the nature of the P2, and below I share a realization I had while exploring this old operational amplifier.
“In my quest to understand the P2, I took a journey towards my inner self. Not being able to afford a trip to Kathmandu, I simply meditated in front of the test bench with all instruments turned on. After hours of humming [mostly from the step-down transformers in the power supplies] and pensive silence, I hit an epiphany. My arrogance and narcissism has led me to live a life of self-centeredness. But at the bottom of it all, it wasn’t really all about me, it’s all about the P2. In order to fully grasp the concept of the P2, I must feel the P2, act like the P2, become the P2! I rejoiced over my realization. With newfound strength, I set the SMU to “Pulse” mode, held the terminals with b…

An Amateur’s View on the P2 [Part 1]

The P7 was the first prototype for an op-amp to use a varactor diode bridge as a means of producing an error signal amplified by transistors (rather than the conventional vacuum tubes or the later FETs). Conceptualized by George A. Philbrick (or Lewis R. Smith?), the prototype was simplified (well, a nitpicker may argue the extra circuit current) by Bob Malter resulting in one of the most profitable operational amplifiers ever to be sold, the P2.
Sporting input bias currents in the pA range (1x10e-12), the P2 drove a $220 demand, which was 1/8 to ½ (my source for this one is obscure) the price of a VW Beetle at the time. The cost of building a P2 paralleled that of a cheap radio – around $10 to $15, so you can just imagine how lucrative things were. The P2 dominated for 30 years, becoming obsolete only after the release of the LMC660, which now offers input bias currents at the fA range (1x10e-15).
My interest for the P2 was piqued once more by Paul Rako’s great post “What’s All this…