Electronic Design published my first Idea for Design, “AC-DC Converter Runs Off One Power Supply” (April 16, 1992, p. 93), more than 16 years ago (Fig. 1). It set a theme that I have continued to employ ever since—using the nifty venue of IFDs to present and develop new circuit design ideas and themes to the engineering community. Over the years, examples of some of those basic concepts and the IFDs that showcased them (which are still available at www.electronicdesign.com) still stand out.
Take Back Half
High-performance temperature control looks easy enough in theory, but is far from simple in practice. The Take Back Half (TBH) method takes deliberate advantage of the (approximate) equality of straightintegration’s undamped over/undershoots (Fig. 2).
Experience gained from applying TBH reveals that the algorithm’s stability is robust. Simulation and experimentation agree that convergence can always be achieved while steady-state error remains equal to zero. Four of my IFDs use TBH:
• “Take Back Half: A Novel Integrating Temperature- Control Algorithm,” Dec. 4, 2000, p. 132-134, ED Online 4994
• “Precision Thermostat Uses TBH and AC Feed- Forward Compensation,” March 19, 2001, p. 126-128, ED Online 4129
• “‘Take-Back-Half’ HVAC Thermostat Is Precise and Energy Efficient,” July 9, 2001, p. 100-102, ED Online 3850
• “Thermostat for High-Altitude Atmospheric Sampler is Fault-Tolerant,” Nov. 19, 2001, p. 88-90, ED Online 3523
Among the techniques for measuring airspeed, thermal anemometry has the virtues of simplicity and easy miniaturization (Fig. 3). Thermal airspeed sensors face two practical problems, though. First, the accuracy of the thermal airspeed measurement depends on accurate compensation for ambient temperature, and accurate temperature measurement isn’t easy, so portable operation is problematic. Next, the second-order exponent makes the raw sensor output nonlinear with airspeed. So, thermal anemometers typically need some provision for measurement linearization. Five of my IFDs look at these problems:
• “Portable Airspeed Measurement,” Jan. 22, 1996, 92-94, ED Online 19696
• “Linear Pitot-Tube Air-Speed Indicator,” June 9, 1997, p. 164-166, ED Online 6396
• “Low Power Thermal Airspeed Sensor,” May 25, 1998, p. 116-118, ED Online 6292
• “Low-Power Solid-State Airflow Detector,” Jan. 22, 2001, p. 118-125, ED Online 4294
• “Series-Connected Transistors Use Differential Heating to Sense Airflow,” May 7, 2001, p. 99-100, ED Online 3990
Self-Compensating Charge Pump
The classic diode-capacitor charge pump is one of the many starting points for voltageto- frequency converter designs (Fig. 4). An obvious snag with this scheme is the need to cope with the forward voltage drop of VD of the pump diodes, including the associated temperature dependence. But commonly used methods for doing so sometimes run into trouble caused by parasitic capacitiance. Two IFDs illustrate a different VD fix, in which multiple diodes work together to make a compensatory charge pulse. Not only do we get compensation for the bothersome VDs, but the effects of stray capacitance also get rubbed out.
• “Nanopower VFC Includes Self- Compensating Charge Pump,” June 22, 1998, p. 131, ED Online 6283
• “Available-Light Phototachometer Simplifies Outdoor Remote Sensing,” Jan. 25, 1999, p. 96-97, ED Online 6237