By: David W. Hess (dwhess.delete@this.banishedsouls.org), September 27, 2007 5:31 pm
Room: Moderated Discussions
Jonathan Kang (johnbk@gmail.com) on 9/27/07 wrote:
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>David W. Hess (dwhess@banishedsouls.org) on 9/27/07 wrote:
>---------------------------
>>Why would latch-up be an additional problem? Isn't that just an aspect of circuit
>>design and process? I have only had to deal with it in old op-amp and comparator
>>designs as well as CMOS processes that suffer from their parasitic SCR structure.
>
>Sorry, I meant for CMOS. I've hardly worked in any other process so my thinking
>automatically goes to what problems (bi)CMOS would have.
Early integrated bipolar op-amp and comparator designs often suffered from non-destructive latch up. Simple JFET input op-amps usually suffer a similar problem with the output undergoing phase inversion if the input common mode voltage exceeds the input common mode range.
CMOS process related latchup can of course be very destructive and is often better described then witnessed.
>>Testing fast devices is actually more difficult from one perspective because parts
>>like tunnel diodes which can be used in fast pulse generators have gotten much more
>>difficult to find. The replacement in these applications is naturally the emitter coupled multivibrator.
>
>I've only worked in high-speed digital so it may be different for RF or other types
>of signals, but we generally test a high-speed driver/receiver with an LFSR signal
>going in rather than a pulse. This, of course, means we'd have to build both a
>transmitter and receiver but a lot of the technology that goes into one can go into the other.
Fast rise and fall time sources are used for fixture and instrument calibration and their design is almost an art form. Tunnel diodes were often used to get into the picosecond range but with their increasingly tenuous availability, I have seen emitter coupled multivibrators use RF bipolar transistors for the same purpose.
I suspect the transconductance advantage that bipolar transistors enjoy over CMOS prevents the later from supplanting the former in this type of application.
---------------------------
>David W. Hess (dwhess@banishedsouls.org) on 9/27/07 wrote:
>---------------------------
>>Why would latch-up be an additional problem? Isn't that just an aspect of circuit
>>design and process? I have only had to deal with it in old op-amp and comparator
>>designs as well as CMOS processes that suffer from their parasitic SCR structure.
>
>Sorry, I meant for CMOS. I've hardly worked in any other process so my thinking
>automatically goes to what problems (bi)CMOS would have.
Early integrated bipolar op-amp and comparator designs often suffered from non-destructive latch up. Simple JFET input op-amps usually suffer a similar problem with the output undergoing phase inversion if the input common mode voltage exceeds the input common mode range.
CMOS process related latchup can of course be very destructive and is often better described then witnessed.
>>Testing fast devices is actually more difficult from one perspective because parts
>>like tunnel diodes which can be used in fast pulse generators have gotten much more
>>difficult to find. The replacement in these applications is naturally the emitter coupled multivibrator.
>
>I've only worked in high-speed digital so it may be different for RF or other types
>of signals, but we generally test a high-speed driver/receiver with an LFSR signal
>going in rather than a pulse. This, of course, means we'd have to build both a
>transmitter and receiver but a lot of the technology that goes into one can go into the other.
Fast rise and fall time sources are used for fixture and instrument calibration and their design is almost an art form. Tunnel diodes were often used to get into the picosecond range but with their increasingly tenuous availability, I have seen emitter coupled multivibrators use RF bipolar transistors for the same purpose.
I suspect the transconductance advantage that bipolar transistors enjoy over CMOS prevents the later from supplanting the former in this type of application.
