App Note 98 part 1

Signal sources, conditioners and power circuitry: Circuits of the fall, 2004. 28 pages.

This app note is another circuits collection of more-or-less random projects, as he has previously done in App Note 45, App Note 61, and App Note 75.

The app note starts with a simple implementation of a current source in Figure 1. The real application circuit in Figure 2, produces "alternating, equal amplitude, opposed polarity linear capacitor ramps". An interesting choice for the output waveform: I wonder what this signal was used for?

Figure 4 shows a simple sine-wave oscillator (well, really a heavily filtered triangle-wave oscillator). I think the interesting piece of this circuit is the use of the one-sided output from the single-supply A3 to implement half-wave rectification in the amplitude-control loop. Cheesy, but clever.

Figure 6 shows a wide-band high-voltage level shifter, capable of producing 50-volt pulses without overshoot. The footnote exposes a brave design choice:

Transistor data sheet aficionados may notice that the –50V potential exceeds Q1, Q2, Q3 VCEO specifications. The transistors operate under VCER conditions, where breakdown is considerably higher.

The next few circuits include several different pulse generators. He seems to be exploring a wide array of alternatives to his usual avalanche-based pulsers (such as Appendix B in App Note 79). Figure 8 uses a single-chip oscillator that achieves a 400-ps rise time (as shown in Figure 10) and a 320-ps fall time (Figure 11). Nice and simple. Figure 12, inspired by the calibrator circuit from the Tektronix 485 oscilloscope, produces a 850-ps rise time, with a flat-top pulse. Clean and pretty. Figure 15 uses a unique (and discontinued) HP tunnel diode to produce a 20-ps (twenty! picoseconds!) rise time. Yikes. Figure 19 produces pulses with controlled widths, down to 1 ns.

The next three circuits are instrumentation applications. Figure 25 shows a single-supply amplifier, which uses the chopper-clock output to drive a charge pump to allow true-zero-volt output swing. This circuit is them used in the milliohmmeter in Figure 27 and the instrumentation amplifier in Figure 30.

Figure 32 show a wide-band low-feedthrough switch using transconductance amplifiers, developed for settling time measurement (we'll see this circuit again in App Note 120).

I'll cover the rest of the circuits next time.