# Buffers

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#### Atomic_Sheep

##### Member
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

##### Well-Known Member
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

##### Well-Known Member
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

##### Well-Known Member
A buffer has no voltage gain but has plenty of output current.

#### tomizett

##### Active Member
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

##### Well-Known Member
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.

#### Atomic_Sheep

##### Member
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

##### Well-Known Member
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.

#### Atomic_Sheep

##### Member
Yep good point.

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