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I already know it is not a schmitt trigger, it looks like it is used as an open loop amplifier taking a reference voltage on the (+) and the V0 is fed into a schmitt trigger.

enter image description here

I have no other data. I wonder if it is "made up" like the symbol in comparator schematic symbol.

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  • \$\begingroup\$ It is clearly not a schmitt trigger because the schematic uses a different (proper) symbol for it, and a scmitt trigger is esentially a comparator with hysteresis. \$\endgroup\$ Aug 25 '14 at 15:09
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    \$\begingroup\$ I've seen it used in schematics so the reader can instantly knows the output is either a 1 or a 0. This disagrees with your amplifier conclusion so I guess a circuit would be helpful. \$\endgroup\$
    – ACD
    Aug 25 '14 at 15:15
  • \$\begingroup\$ That is not the symbol for hysteresis, but a symbol for "positive-edge". May indicate that the comparator output is being used as an edge trigger. \$\endgroup\$
    – Tut
    Aug 25 '14 at 15:36
  • \$\begingroup\$ I cannot share the whole schematic (work restrictions), sorry. \$\endgroup\$ Aug 25 '14 at 15:47
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    \$\begingroup\$ See engr.uidaho.edu/thompson/courses/ME330/lecture/… ... It appears to be a symbol for an analog comparator, probably used to differentiate it from an opamp. (link provided by endolith) \$\endgroup\$
    – Tut
    Aug 25 '14 at 15:50
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The second block in your schematic is clearly a inverter with Schmitt trigger input. Since the first block was presumably drawn by the same person, I think they are trying to point out that it does NOT exhibit hysteresis, in contrast to the second block. That's a guess, but I think makes sense. Usually one doesn't draw anything special to indicate a block has a normal "linear" response.

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    \$\begingroup\$ Many comparators have open-collector outputs; this can sometimes lead to confusion as to whether the output should be considered "on" or "off" when the "+" input exceeds the "-" input. Perhaps the rising-edge symbol indicates that the output voltage should be a logic high when "+" exceeds "-". \$\endgroup\$
    – supercat
    Aug 25 '14 at 17:14
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It is a push-pull open-drain output comparator. It has an internal input hysteresis which eliminates output switching due to internal input noise voltage, reducing current draw. ACD's digital output comment and supercat's input exceding rail voltage comment were very informative and correct.

But as far as I can tell, no manufacturer uses this symbol. Even the datasheet for the component in the actual circuit.

It should also be noted the schematic is missing a pull up resistor.

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