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clamping diodes on the input pins of logic IC chips

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calton57

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I always see these clamping diodes on the input pins of logic IC chips, mostly for TTL chips, any reasons why for TTL logic chips and not for CMOS logic chips?

The Clamping diodes are to protect the Input pins of the logic IC chips to go into the "negative region" which will damage the input section of the IC chip. Any reasons why the Logic IC chip doesn't like a negative voltage?

They make amplifiers with one transistors that swings both positive and negative voltages, but they use DC offset so the negative cycle voltage is not below ground or zero voltage.

What are some signals or Logic IC chips causes a negative voltage on the input to logic circuits or to a logic IC chips?

I read that Flip flops cause a negative output voltage signal which damages IC TTL logic chips, any reasons why flip flop chips output a negative signal or they call it a ringing
 

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I always see these clamping diodes on the input pins of logic IC chips, mostly for TTL chips, any reasons why for TTL logic chips and not for CMOS logic chips?

The Clamping diodes are to protect the Input pins of the logic IC chips to go into the "negative region" which will damage the input section of the IC chip. Any reasons why the Logic IC chip doesn't like a negative voltage?
Forward bias of the substrate. Can result in large current flow thereby destroying the input transistors.

What are some signals or Logic IC chips causes a negative voltage on the input to logic circuits or to a logic IC chips?

I read that Flip flops cause a negative output voltage signal which damages IC TTL logic chips, any reasons why flip flop chips output a negative signal or they call it a ringing
It's called overshoot and undershoot, it can occur or get really really bad when there is an impedance mismatch between the driver, receiver, and the trace. The higher the edge rate of the transitioning signal means the higher the frequency components of the signal, which results in reflections on the transmission line if it's not terminated or impedance matched correctly. And it's not just Flip-Flops it's any high speed digital signal.
 

calton57

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So the higher the switching speed their will be overshoot and undershoot? but what is causing the overshoot and undershoot? its creating spikes and transients

The clamping diodes Forward bias of the substrate?
 

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Here's an animation of a reflection on a transmission line http://www.williamson-labs.com/xmission.htm

The clamp diode is there to prevent the substrate from conducting current, which would damage the part. It's not there to forward bias anything.
 

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