AN504 Ver la hoja de datos (PDF) - Vishay Semiconductors

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componentes Descripción

Fabricante

AN504

Video Crosspoint Switch Simplifies Large Matrix Designs

Vishay Semiconductors 

AN504

Vishay Siliconix

Logic

Control

RS

VIN

Q

Input

CGS1

RDS1

CGS3

IS(on)

CGS2

RDS2

CGS4 RDS4

CGD4

Output

ID(on)

RL

Q

Logic

Control

Q

Input

FIGURE 3. On-State Model

CGS1

CGS2

Substrate (V–)

CGS4

CGD4

Output

CGS3

RS

IS(on)

VIN

RDS3

RL

ID(on)

Q

Note: Individual drain-source capacitances not shown for clarity.

Substrate (V–)

FIGURE 4. Off-State Model

Figures 3 and 4 show low-frequency models of an “on”

channel and an “off” channel, respectively. The models allow

us to visualize the effects of leakage, low-frequency

transmission loss, and analog overvoltage on the overall

circuit performance. The term “low-frequency” is used for the

models because they use single components to represent the

characteristics of the channel. In other words, components

distributed over an area of silicon are lumped together for

simplicity’s sake. An accurate high-frequency model of an “on”

channel demands a more complex RC network (more on this

later).

www.vishay.com S FaxBack 408-970-5600

6-2

Leakage-Generated Offsets

Depending on the value of source and load impedances

connected to input and output, leakage-generated offset

voltages can be obtained using Ohms Law. In practice,

however, the DG884 will be used surrounded by fast linear

circuitry whose bias currents will be much higher than the

nanoampere leakage currents of the D/CMOS process. Thus,

offset voltages will be dominated by the external circuitry

around the crosspoint and not the DG884.

Document Number: 70610

05-Aug-99

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