Polysilicon gate in .NET Drawer ean13+5 in .NET Polysilicon gate

Polysilicon gate using vs .net todevelop ean-13 supplement 2 in web,windows application Web application framework Source Drain W xd Ld xd Gate-bulk overlap (a) Top view Gate oxide tox n+ (b) Cross section L n+ Figure 3.28 MOSFET overlap capacitance. C GSO = C GDO = C ox x d W = C o W (3.45). Since xd is a technology-de termined parameter, it is customary to combine it with the oxide capacitance to yield the overlap capacitance per unit transistor width Co (more specifically, Cgso and Cgdo). Channel Capacitance Perhaps the most significant MOS parasitic circuit element, the gate-to-channel capacitance CGC varies in both magnitude and in its division into three components CGCS, CGCD, and CGCB (being the gate-to-source, gate-to-drain, and gate-to-body capacitances, respectively), depending upon the operation region and terminal voltages. This varying distribution is best explained with the simple diagrams of Figure 3.

29. When the transistor is in. Page 110 Friday, January 18, 2002 9:00 AM THE DEVICES 3 . cut-off (a), no channel exi sts, and the total capacitance CGC appears between gate and body. In the resistive region (b), an inversion layer is formed, which acts as a conductor between source and drain. Consequently, CGCB = 0 as the body electrode is shielded from the gate by the channel.

Symmetry dictates that the capacitance distributes evenly between source and drain. Finally, in the saturation mode (c), the channel is pinched off. The capacitance between gate and drain is approximately zero, and so is the gate-body capacitance.

All the capacitance hence is between gate and source.. G CGC S (a) cut-off D S (b) resistive G CGC D S (c) saturation G CGC D Figure 3.29 The gate-to-cha nnel capacitance and how the operation region influences is distribution over the three other device terminals..

To actual value of the tota .net vs 2010 EAN13 l gate-channel capacitance and its distribution over the three components is best understood with the aid of a number of charts. The first plot (Figure 3.

30a) captures the evolution of the capacitance as a function of VGS for VDS = 0. For VGS = 0, the transistor is off, no channel is present and the total capacitance, equal to WLCox, appears between gate and body. When increasing VGS, a depletion region forms under the gate.

This seemingly causes the thickness of the gate dielectric to increase, which means a reduction in capacitance. Once the transistor turns on (VGS = VT), a channel is formed and CGCB drops to 0. With VDS = 0, the device operates in the resistive mode and the capacitance divides equally between source and drain, or CGCS = CGCD = WLCox/2.

The large fluctuation of the channel capacitance around VGS=VT is worth remembering. A designer looking for a well-behaved linear capacitance should avoid operation in this region..

WLCox WLCox CGC CGCS 2WLCox 3 WLCox 2 CGCB CGCS = CGCD WLCox 2 CGCD VGS VT (a) CGC as a function of VGS (with VDS=0) Figure 3.30 VDS/(VGS-VT). (b) CGC as a function of the degree of saturation Distribution o f the gate-channel capacitance as a function of VGS and VDS (from [Dally98]).. Once the trans .NET EAN-13 istor is on, the distribution of its gate capacitance depends upon the degree of saturation, measured by the VDS/(VGS-VT) ratio. As illustrated in Figure 3.

30b,. Page 111 Friday, January 18, 2002 9:00 AM Section 3.3 The MOS(FET) Transistor CGCD gradually .net framework European Article Number 13 drops to 0 for increasing levels of saturation, while CGCS increases to 2/3 CoxWL. This also means that the total gate capacitance is getting smaller with an increased level of saturation.

From the above, it becomes clear that the gate-capacitance components are nonlinear and varying with the operating voltages. To make a first-order analysis possible, we will use a simplified model with a constant capacitance value in each region of operation in the remainder of the text. The assumed values are summarized in Table 3.

4.. Table 3.4 Aver age distribution of channel capacitance of MOS transistor for different operation regions. CGCB CoxWL 0 0 CGCS 0 CoxWL / 2 (2/3)CoxWL CGCD 0 CoxWL / 2 0 CGC CoxWL CoxWL (2/3)CoxWL CG CoxWL+2CoW CoxWL+2CoW (2/3)CoxWL+2CoW.

Operation Region Cutoff Resistive Saturation Example 3.9 Us ing a circuit simulator to extract capacitance Determining the value of the parasitic capacitances of an MOS transistor for a given operation mode is a labor-intensive task, and requires the knowledge of a number of technology parameters that are often not explicitly available. Fortunately, once a SPICE model of the transistor is attained, a simple simulation can give you the data you are interested in.

Assume we would like to know the value of the total gate capacitance of a transistor in a given technology as a function of VGS (for VDS = 0). A simulation of the circuit of Figure 3.31a will give us exactly this information.

In fact, the following relation is valid:. I = C G(V GS).
Copyright © . All rights reserved.