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How are CMOS switches implemented in digital circuits?

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abhigopal

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Hi
i have a couple of basic questions

1. How are swithes implemented in digital circuits. by switch i mean just a normal on/off connection (not a MUX).. I know of one way which is by the use of transmission gates.. is there any other way

2. How does switching take place.. meanin. what is the power consumed for switching. . is it just the one transition of a gate from 0-1?

thanks in advance
abhi
 

site:www.edaboard.com cmos switch

1- first question is very strange - maybe i didnt get it -
anyway, u can use a single PMOS or NMOS as ur switch (on -off) using its gate voltage , but it's performance will differ for one and zero for both NOMS and PMOS, therfore they made the transmission gate to combine both benfiets with one and zero.

2- for power consumption there will be static power and dynamic one,
u care the dynamic one p = c f v^2

check this for more
**broken link removed**
 

Re: CMOS switches

The answer to first Qn. is same:
you can use n/p-mosfets as switches with the controlling signal at the gate. Transmission gates are better swithes in that they dont degrade the voltage levels of the signals.

regarding power consumption.

there are two kind of power consumption in the IC devices.
1. Static : in static mode : due to a direct path b/n VDD and GND and leakage.
2. Dynamic : while switching :
this in turn is of two types
a). during charging/discharging of the output load. p= 1/2 CVF2.
b). power dissipated in the MOS devices when current flows.

you can google it.
 

CMOS switches

use this chip
cd4066

regards
 

CMOS switches

switches are implement by P or N nmos or both of them due to their better conductance. but in analog circuits such as A/D some complicate switches are used to prevent distortion(Vgs=Vdd).
 

CMOS switches

I think the best device used for switching is the MOSFET cos it consume very small power
 

CMOS switches

for small signals, you can realize switching by using switching transistors and MOSFETs. for power applications(high voltage and current), you can use MOSFET, IGBT(insulated gate bipolar transistor),thyristor, GTO(gate turn off thyristor).you drive the device by controlling the gate voltage.(or current for thristor)
 

CMOS switches

Transmission gates maynot be used in low voltage design.
NMOS or PMOS can be used seperately in case of low voltage
 

Re: CMOS switches

1) you also can implement a switch by a N mosfet.

2) you are right.

best regards



abhigopal said:
Hi
i have a couple of basic questions

1. How are swithes implemented in digital circuits. by switch i mean just a normal on/off connection (not a MUX).. I know of one way which is by the use of transmission gates.. is there any other way

2. How does switching take place.. meanin. what is the power consumed for switching. . is it just the one transition of a gate from 0-1?

thanks in advance
abhi
Click to expand...
 

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