Please explain the difference between body effect and body bias.
Body bias is the voltage at which the body terminal (4th terminal of mos) is connected. Body effect occurs when body or substrate of transistor is not biased at same level as that of source. (basically formation of PN junction diode in case of NMOS as example). Detail can be obtained from this video.
http://www.youtube.com/watch?v=m-4YUDbRc6k
=the voltage of the substrate w.r.t. the source of a CMOS device. Usually it is grounded but you can bias it to some voltage to adjust Vth of the device.
A/
The change in the threshold voltage of the MOS Transistor because of the non zero bias to the body is called Body Effect. It is represented by gamma and has units of rootV
Body effect refers to the change in the transistor threshold voltage (VT) resulting from a voltage difference between the transistor source and body.Because the voltage difference between the source and body affects the VT, the body can be thought of as a second gate that helps determine how the transistor turns on and off.
Body bias involves connecting the transistor bodies to a bias network in the circuit layout rather than to power or ground.The body bias can be supplied from an external (off-chip) source or an internal (on-chip) source.
Nice explanation by Amir Mahdi....but so far i have seen only three pins for mosfets and body is internally connected to Source...
Is there any mosfets which do have a separate (external)Body pin?
To the above comments, MOSFETs do have only 3 pins but the body/substrate is the metal panel that you see behind the MOSFET. You can bias it with what can be called the body voltage.
But it is interesting to note that most MOSFETs available in the market already have the body-source shorted and hence VSB is already put to zero, and it may be hard to observe the required effect.
The MOSFET transistor has a backgate connected to its substrate also called bulk of the transistor. This backgate or bulk electrode is normally connected to the source. In this case the transistor will have a threshold voltage called Vth0 which means the threshold voltage with bulk bias equal to zero. However, one can change the threshold voltage by a reverse gate bias which leads to an increase in the threshold voltage. So, the body effect is accomplished by its bias.
For more details about the body effect and the threshold voltage of the transistor please refer to the book:Book Electronic Devices
Best wishes
Because Drain and Source are of same type (N-type in case of NMOS) and Body/Substrate/Bulk is of opposite type therefore it makes two diodes ( one between drain and substrate, other between source and substrate). if both the diodes are forward biased, it will not allow to turn the MOS ON, therefore we make one diode reverse biased (source to substrate diode) for turning MOS ON.
Body bias is used to dynamically adjust the threshold voltage (Vt) of a CMOS transistor. While CMOS transistors are usually thought of as having three terminal devices, with terminals for the source, gate, and drain, it’s increasingly common to have a fourth terminal connected to the body (substrate). Because the voltage difference between the source voltage (Vs) and body voltage (Vb) affects the Vt, the body can be thought of as a second gate that helps determine how a transistor turns on and off.
Should we consider body effect in our experiments? Is there body effect in CMOS devices?
So there is body effect in chips like FPGAs. Is it ture?
Without considering body effect the Threshold voltage of NMOS transistors equals Vdd/2 for 45nm and smaller technologies, however by considering the body effect the Threshold voltage of NMOS transistors will be increased. How much will it be increased?
Could you please guide me in this regard?
The body effect is the threshold voltage variation due to the bulk/source voltage.
To cancel the body effect you need to tie both S and B to the same potential.
In addition, the body effect increases the threshold voltage if you have a positive Vb
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