# unable to understand a symbol

#### rohit75

Joined Nov 28, 2013
1
In this circuit, there is a current source Ib.
Its one end is connected to the circuit.
While the other end goes out to an arrow.
What does this arrow signify?
Should I connect it to Vcc i.e. +5 V DC or AC GND or if not, then where?

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#### t06afre

Joined May 11, 2009
5,934
Ib is a constant current source

#### MrChips

Joined Oct 2, 2009
21,373
You are not really planning on building this, are you?

Joined Apr 30, 2011
1,569
This looks like a representation of part of the internal circuitry of an op amp or comparator but it's not a complete (buildable) schematic.

#### t06afre

Joined May 11, 2009
5,934
Looks like some sort of an analog multiplier function

#### WBahn

Joined Mar 31, 2012
25,927
In this circuit, there is a current source Ib.
Its one end is connected to the circuit.
While the other end goes out to an arrow.
What does this arrow signify?
Should I connect it to Vcc i.e. +5 V DC or AC GND or if not, then where?
Ib is a current source and all that matters, as far as this circuit is concerned, is the current coming out of it and going into the input transistor. So you can use any circuit that will produce Ib. That might be as simple as a resistor to Vcc.

This circuit relies on close matching of the transistor parameters and, hence, is only suitable for fabrication on an IC. If you want to build a circuit like this using discrete parts, you need to us ballast resistors in a number of places to force adequate matching in the mirrors.

#### #12

Joined Nov 30, 2010
18,210
you can use any circuit that will produce Ib. That might be as simple as a resistor to Vcc.
I interpret the current supply to be a negative supply (electrons arriving at the arrow in question) because M7 is a P type, so drain voltage will be negative.

Do you think I am correct?

#### WBahn

Joined Mar 31, 2012
25,927
M7 is an NFET. M5 is a PFET.

Note that the diode arrow that is part of the symbol is not going from the channel to the bulk, but rather from the channel to the source.

#12

#### #12

Joined Nov 30, 2010
18,210
Oh, I get it. The placement of the arrow is as important as the direction of the arrow. Thank you.

#### Ramussons

Joined May 3, 2013
828
In this circuit, there is a current source Ib.
Its one end is connected to the circuit.
While the other end goes out to an arrow.
What does this arrow signify?
Should I connect it to Vcc i.e. +5 V DC or AC GND or if not, then where?
It's not an arrow - It's a ground symbol upside down - the substrate.

Ramesh

#### WBahn

Joined Mar 31, 2012
25,927
It's not an arrow - It's a ground symbol upside down - the substrate.

Ramesh
That could well be. The image doesn't have enough resolution for me to tell if it is a ground symbol or an arrow. It doesn't really matter -- it's just signifying that the other side of the current source goes somewhere. Ground is as good a place as any, although the substrate, in general, is NOT a good place for it to go. While there are exceptions -- and processes designed for those exceptions -- you generally try to keep signal currents out of the substrate.

#### Ramussons

Joined May 3, 2013
828
Ground is as good a place as any, although the substrate, in general, is NOT a good place for it to go. While there are exceptions -- and processes designed for those exceptions -- you generally try to keep signal currents out of the substrate.
Agreed, but since there is no "ground" terminal shown, it will have to be the substrate.

Ramesh

#### WBahn

Joined Mar 31, 2012
25,927
Agreed, but since there is no "ground" terminal shown, it will have to be the substrate.

Ramesh
Why? It's just a generic schematic. Gives no indication of what type of process it is. Might be N-Well, might be P-Well, might be Twin-Well, might be epi or non-epi. Heck, might be SOS.

The current source is just there to indicate a programming current going into M7. As I said before, it might well be nothing more than a resistor to Vcc.