Celebrating Hans Camenzind’s other achievements
On this fourth anniversary of Hans Camenzind’s passing on August 15, 2012, I wanted to highlight some of the other technical achievements he had besides the ubiquitous 555 timer.
A low power version of Camenzind’s 5551
Camenzind’s paper for the IEEE Journal of Solid-State Circuits in December 1978, entitled A Low Voltage IC Timer, co-authored by Richard Kash. Kash joined Fairchild after he got his BSEE in 1976 and later joined Interdesign in 1977. By the time that this paper was presented in 1978, Camenzind had founded Interdesign in 1970 to further his revolutionary ideas for IC design and was President there until 1977 when he founded Tridar to develop a phone that would function as a handheld phone and a speakerphone. Unfortunately, this company did not succeed.
In this design, Camenzind used a neat sensing circuit to achieve the lower threshold and demonstrated that the 555 could function with a supply voltage of under 1 volt with good precision. This functional block could then be added to a then limited collection of low-voltage ICs. Figure 1 is a block diagram of his low-voltage timer.
Figure 1: The block diagram of the low-voltage timer (Image courtesy of Reference 1)
It’s all about the current source design. In n-p-n diode-based current sources like in his original design and other existing IC designs at that time, designers needed to keep the transistors out of saturation so as to not steal current from the other current sources in the architecture of the current source design. Camenzind fashioned a saturation detector from n-p-n transistors because lateral p-n-p transistors would not function properly in sensing a saturation occurance.
Figure 1 shows a timing circuit using Camenzind’s new saturation detection scheme. He uses an external resistor and capacitor to create the timing network. A comparator whose threshold is selectable externally, then sets a flip-flop when an end-of-charge voltage is reached. Then the capacitor is discharged through the n-p-n transistor current source. When this transistor saturates, the trigger circuit is enabled, the flip-flop is reset, and the cycle starts all over again.
A Modulated Pulse Audio Amplifier2
Back in 1966, ten years after the first issue of EDN, Camenzind determined that pulse width modulation (PWM) had great potential advantages in ICs, especially in a conventional audio amplifier which, at that time, was not really suitable for an IC design because of poor efficiency and high power. In Reference 2 he discussed some three different approaches for amplitude to pulse-width conversion circuits.
Camenzind mentions that the maximum theoretical efficiency of a class B amplifier was 78 percent and, in practical circuits, it was difficult to reach an efficiency of more than 60 %. For example, a 5W integrated circuit amplifier design will have 33W of heat produced inside a silicon chip. This heat degrades the reliability of the amplifier as well as limits the minimum chip size.
Integrated class A and B amplifiers would not follow the trend of decreasing costs of that time. Also at that time, conventional amplifiers needed stable biasing points. Designers could use coupling capacitors or transformers to solve that problem; this could not be done in an integrated circuit in 1966. Camenzind knew that there was a method that had been used for 35 years known as Class-D, pulse-width modulation, pulse-duration modulation, or two-state amplification.
In the two-state amplifier, amplification of a signal is enabled by quickly switching an inductive load between a positive and negative voltage. Figure 2 shows that pulse train.
Figure 2: Output waveforms produced by a two-state amplifier, un-modulated (above) and width-modulated (below) (Image courtesy of Reference 2)
Camenzind showed in breadboarded models, using complementary transistors, an efficiency of 89 % was reached at 1W with a +/- 3-dB frequency response from DC to 15 kHz and a distortion of under 1 percent. Just employing n-p-n transistors, Camenzind saw an efficiency of 76% at 1 watt and a +/- 3 dB frequency response from DC to 10 kHz and a distortion of less than 5%.
No external components or heatsinks were needed and a TO-5 transistor case was able to hold the circuit.
- A Low Voltage IC Timer, Hans Camenzind and Richard Kash, IEEE Journal of Solid-State Circuits, December 1978
- Modulated Pulse Audio Power Amplifiers for Integrated Circuits, Hans Camenzind, IEEE Transactions on Audio and Electroacoustics, September 1966
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- 555 timer inventor Hans Camenzind remembered
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