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Buffers

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Hi,

I was just wondering what the little circle next to the triangle for buffers means? Inverted signal? So if there is a circle the signal is inverted, if there is no circle, no inversion?
 

audioguru

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A triangle with a little circle at the pointed end is not a buffer, instead it is a logic inverter that has a lot of voltage gain.
 

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dougy83

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I was just wondering what the little circle next to the triangle for buffers means? Inverted signal? So if there is a circle the signal is inverted, if there is no circle, no inversion?
Hi. Yes, the circle shows that the signal is inverted. No circle = no inversion.
 

audioguru

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A buffer has no voltage gain but has plenty of output current.
 

tomizett

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We should be aware that there is a difference between what is ment by a "buffer" in the contexts of digital and analogue electronics.

In the analogue domain a buffer is an amplifier having a unity voltage gain but, potentially, a current gain over unity.

In the digital domain, a buffer is a logic element with one output whose locic state is identical to that of its single input (although devices such as "tri-state buffers" could be regarded as exceptions). In practice they are generally expected to drive lines or large fan-outs, provide level translation, etc, and so may exhibit both voltage and/or current gain.

Conceptually, both analogue and digital (logic) buffers fulfill similar roles, but electrically they may be very different circuits.

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Regarding the circle, what dougy says is exactly right...
Bare in mind that you might see the circle on inputs as well as outputs, indicating that the input is inverted.
 

audioguru

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Yes, I see on their datasheet that the Cmos buffers, the CD4049 inverting and the CD4050 non-inverting have plenty of voltage gain and also have a higher maximum output current than ordinary Cmos logic.
I have used plenty of Cmos logic ICs but I have never needed and have never used these buffers.
 
I was talking about digital buffers. I did notice the same symbol being used as for logic gates which I found a bit odd. I guess not enough imagination was present when making its symbol :).
 

audioguru

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A logic gate can also invert (with a circle at its rear end) or not (no circle). Non-inverting AND or OR gate, inverting NAND or NOR gate. Some schematics show a circle at an "enable" input to show that it is active low.
 
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