MOSFETs

Thread Starter

Mazaag

Joined Oct 23, 2004
255
In relation to MOSFETs, what do VSS, VDD, VCC, and Vref refer to ? and what is the difference between them

Thanks
 

Papabravo

Joined Feb 24, 2006
14,233
Vss is the voltage at the "source" terminal.
Vdd is the voltage at the "drain" terminal.
Vcc is the voltage at the collector of a bipolar junction transistor, and doesn't strictly have any meaning in a MOSFET circuit.
Vref is usually and A/D converter reference or a comparator referenc voltage, and strictly speaking has no meaningful connection with MOSFETS.

In many circuits with a mix of discrete parts and ICs you will see Vdd and Vcc connected together and be at some voltage between say 1.8 and 5.0 volts.

FYI Vgg is the gate voltage on a MOSFET.
 

Thread Starter

Mazaag

Joined Oct 23, 2004
255
Hi Papa,
Thank you for your reply..


Vref here is refered to as the Reference Voltage. Now i'm looking right now at a DDR I/O block, which uses SSTL.

Would that help determine what Vref is used for..?

Thanks
 

Dave

Joined Nov 17, 2003
6,970
SSTL stands for Stub-Series-Terminated-Logic.

DDR I/O block I would assume is something to do with Double Data Rate RAM (most likely SDRAM), of which SSTL devices are used to drive in computer memory structures.

A bit more clarity may be of use here.

Dave
 

Thread Starter

Mazaag

Joined Oct 23, 2004
255
The problem is that I am working directly from a netlist, and have no schematic to refer to. To add to that, I am not familiar with the components that would be found in such a block. In other words, I have no clue what the inside of this block looks like :S

But anyway, I do know that it Vref happens to be a port on the this, so was wondering if anyone knows what it would be used for.. but appearently its not such a common block.. So no worries :D

Thanks anyways guys
 

n9352527

Joined Oct 14, 2005
1,198
VREF is the reference voltage used at the receiving end of the SSTL as the threshold voltage between logic high and low. Usually, VREF is set at half of VDDQ - VSSQ over external variations such as voltage, process, temperature, etc. It is also highly desirable for VREF to be symmetrical between VOH and VIL. The VTT (termination voltage) also has to very closely match VREF.
 

n9352527

Joined Oct 14, 2005
1,198
VREF is the reference voltage used at the receiving end of the STTL as the threshold voltage between logic high and low. Usually, VREF is set at half of VDDQ - VSSQ over external variations such as voltage, process, temperature, etc. It is also highly desirable for VREF to be symmetrical between VOH and VIL. The VTT (termination voltage) also has to very closely match VREF.
 

Dave

Joined Nov 17, 2003
6,970
VREF is the reference voltage used at the receiving end of the SSTL as the threshold voltage between logic high and low. Usually, VREF is set at half of VDDQ - VSSQ over external variations such as voltage, process, temperature, etc. It is also highly desirable for VREF to be symmetrical between VOH and VIL. The VTT (termination voltage) also has to very closely match VREF.
This link goes some way to diagramatically explaining what n9352527 has described.

Dave
 
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