The Zoo Circuit

Circuit startup or overdrive causes the circuit's AC-coupled feedback to latch. If this occurs, C1 's output goes high. C2 , detecting this via the inverters and the 2.7 M–0.1 μF lag also goes high. This lifts C1 's negative input and grounds the positive input with Q7 , initiating normal circuit action. Because the charge pump is directly coupled to C1 's output, response is fast. This scheme promises both lower temperature drift and lower power. Assuming ideal junction compensation, the remaining uncompensated drift terms are C1 's–120 ppm temperature coefficient and the input resistor. This configuration does nothing to fix the PSRR problem. The only realistic fix for that is to replace R1 with a current source. The current source doesn't have to be very stable but must run with only 2 V of headroom because the circuit has to work down to 6.5 V. The simplest alternative is the monolithic LM134. This three-terminal, resistor-programmable device will function with only 800 mV across it, although it does have a 0.33%/°C temperature coefficient.