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The "decoupled" in this scenario probably refers both to the series capacitor that blocks DC (C24), and the C part of the RC (C23) although it should be "coupling capacitor" for C24 (decoupling is also used to refer to the DC blocking function, but I think it gets confusing this way, as it usually means the other sort that shunts AC to ground) and decoupling for C23 (if anything at all)
The coupling cap is used commonly in audio amplifier circuits to allow one stages input to be independently biased from the previous stages DC output level.

Yes, as long as you supply the opamp with the same voltage as the FPGA pins (e.g. 3.3V, 2.5V, etc) rather than the 5V shown. You should be able to use pretty much any opamp for the comparator function (rail to rail is preferable to make things easy, as Steven says, but not essential as long as you meet FPGA input min-high max-low)

The "decoupled" in this scenario probably refers both to the series capacitor that blocks DC (C24), and the C part of the RC (C23) although it should be "coupling capacitor" for C24 (decoupling is also used to refer to the DC blocking function, but I think it gets confusing this way, as it usually means the "other sort" that shunts AC to ground) and "decoupling" for C23 (if anything at all)
The coupling cap is used commonly in audio amplifier circuits to allow one stages input to be independently biased from the previous stages DC output level.

Yes, as long as you supply the opamp with the same voltage as the FPGA pins (e.g. 3.3V, 2.5V, etc) rather than the 5V shown. You should be able to use pretty much any opamp for the comparator function (rail to rail is preferable to make things easy, as Steven says, but not essential as long as you meet FPGA input min-high max-low)

The "decoupled" in this scenario would probably refer to the series capacitor that blocks DC, although it should be "coupling capacitor" (decoupling is also used to refer to the DC blocking function, but I think it gets confusing this way, as it can mean the other sort that shunts AC to ground)
This is used commonly in audio amplifier circuits to allow one stages input to be independently biased from the previous stages DC output level. In the "tape earphone" circuit C24 performs this function. I'm not sure about the "tape input" bit though, as the tape recorders input circuit should have a coupling capacitor in place anyway (maybe it means this, but it does say "prior to..") It looks just like a RC attenuating circuit to me.

Yes, as long as you supply the opamp with the same voltage as the FPGA pins (e.g. 3.3V, 2.5V, etc) rather than the 5V shown. You should be able to use pretty much any opamp for the comparator function (rail to rail is preferable to make things easy, as Steven says, but not essential as long as you meet FPGA input min-high max-low)

The "decoupled" in this scenario probably refers both to the series capacitor that blocks DC (C24), and the C part of the RC (C23) although it should be "coupling capacitor" for C24 (decoupling is also used to refer to the DC blocking function, but I think it gets confusing this way, as it usually means the other sort that shunts AC to ground) and decoupling for C23 (if anything at all)
The coupling cap is used commonly in audio amplifier circuits to allow one stages input to be independently biased from the previous stages DC output level.

Yes, as long as you supply the opamp with the same voltage as the FPGA pins (e.g. 3.3V, 2.5V, etc) rather than the 5V shown. You should be able to use pretty much any opamp for the comparator function (rail to rail is preferable to make things easy, as Steven says, but not essential as long as you meet FPGA input min-high max-low)

The "decoupled" in this scenario would probably refer to the series capacitor that blocks DC, although it should be "coupling capacitor". This is used commonly in audio amplifier circuits to allow one stages input to be independently biased from the previous stages DC output level. In the "tape earphone" circuit C24 performs this function. I'm not sure about the "tape input" bit though, as the tape recorders input circuit should have a coupling capacitor in place anyway (maybe it means this, but it does say "prior to..") It looks just like a RC attenuating circuit to me.

Yes, as long as you supply the opamp with the same voltage as the FPGA pins (e.g. 3.3V, 2.5V, etc) rather than the 5V shown. You should be able to use any opamp for the comparator function.

The "decoupled" in this scenario would probably refer to the series capacitor that blocks DC, although it should be "coupling capacitor" (decoupling is also used to refer to the DC blocking function, but I think it gets confusing this way, as it can mean the other sort that shunts AC to ground)
This is used commonly in audio amplifier circuits to allow one stages input to be independently biased from the previous stages DC output level. In the "tape earphone" circuit C24 performs this function. I'm not sure about the "tape input" bit though, as the tape recorders input circuit should have a coupling capacitor in place anyway (maybe it means this, but it does say "prior to..") It looks just like a RC attenuating circuit to me.

Yes, as long as you supply the opamp with the same voltage as the FPGA pins (e.g. 3.3V, 2.5V, etc) rather than the 5V shown. You should be able to use pretty much any opamp for the comparator function (rail to rail is preferable to make things easy, as Steven says, but not essential as long as you meet FPGA input min-high max-low)