THE 555 TIMER IC

An Interview with Hans Camenzind

 

Oral History Hans Camenzind

Continued)

 

I read your article in the IEEE Spectrum and noticed you provided a detailed description of the design process you used for the 555. How has the IC design process changed since then?

Incredible! The design process itself for the 555 took a year, from start to prototypes and small production quantities. Now, it was right the first time, but that was just luck. I have gone through so many projects where you have teams of people, two people each with one looking at the circuit diagram and the other checking back and forth maybe three teams checking in succession, and there were still mistakes. So, in this case, I had to do it all myself. I was a one man design house, and I got it right the first time. I think that was luck I may have spent extra time doing it because it was my project. There was no way at that time to make absolutely sure you had it right.

 

In the IEEE Article, you mentioned that there was a design review at Signetics. Was that a contractual obligation?

No. I just thought it was a good idea. Ive always had design reviews for all my designs. Get feedback, bounce off ideas with colleagues. But, just how laborious the design was. First, the breadboarding of the circuit. The one thing you want to do is make sure the circuit works well in production, and in production you have parameter variation - high gain, low gain for transistors, high resistor values, low resistor values, all sorts of combinations.

 

 

 

Oral History Hans Camenzind

(Continued)

 

So, in the breadboard, all you can do is build the first one and it works. And then you start plugging in other components. You know, maybe ten different sets, at least, to make sure you get the variations. You still cant be sure you get all of the variations. This is what I did with the breadboard, and this just takes months.

 

If you didnt do this well, there might be a bad outcome in production?

Matter of fact, that was the rule, rather than the exception. You see, there are so many lazy designers that build a breadboard, or nowadays, do a simulation, and not worry about the variations. A circuit may work fine the first time (they were lucky), and then in production they have problems, yield loss. And thats why you see so many revision letters. I have circuits that go to M in production, afterwards, for the first two or three years, with revision after revision.

 

The second stage is where you have a circuit diagram and youre pretty confident it will work. Now you have to make a layout. The only choice I had was to buy a large drafting board, and just draw it out. You know, you want to shift the components around so you have a minimum total area. You may make ten different drawings. Another few months gone!

 

 

 

Go To Camenzind Oral History,Page 8

 

 

 

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