Top 7 bizarre Applications of Mosfet |and its features.

Hello everyone, hope you all are doing great. Consequently, The topic for today is the applications of MOSFET. However this particular time I am considering that you all are clear with all the basics about a MOSFET. But if haven’t then I highly recommend first read the article given below and then come back here;


All about MOSFET


Subsequently, we are now clear with all the basics which are in need so let’s straight jump into the core.

Applications of Mosfet

1. Applications of Mosfet as Switch

  • Mosfet mainly shows three type of region of operation i.e. active, non-saturation and cut-off.
  • among these when mosfet is to be operated as switch it must shift between active and cut-off region.applications of mosfet as a switch
  • This is because in cutoff region 0 current flows through the circuit whereas in active region a constant current flows through in the same vein as that when the switch is off and on respectively.
  • firstly, assume that Vgs is less then Vt due to this there will be no channel present and hence as a result large impedance will be occur this in turn results in no flow of current i.e the switch is open.

Vo = Id * Rd

Ron = ∂Vds / ∂Id

  • Now consider that Vgs is greater than Vt. which means that the mosfet is operating in active region which in turn means that the current flowing throughout the circuit is constant i.e. the switch act as close.

Vds = Vgs – Vt

Id = [(K’W)/L] [2(Vgs – Vt) Vds – (Vds2 )/2]

Roff = ∞

  • Thus the mosfet can be operated as switch.

Application

  • High Efficiency due to this the switching rate increases.
  • Power requirement is low because it draws zero current.

Applications of Mosfet as a Diode/ Active Resistance

Whenever the gate and the drain terminal of the MOSFET are shot together its V-I characteristics are similar to that of a PN Junction diode. Thus it has the name MOS Diode.Application of mosfet as a diode or as a active resistance

Above all, for these applications, Mosfet must operate in the saturation region.

I = Id = [(K’W)/2L] * [(Vgs – Vt)2]

Connecting gate to drain in other words which means Vds controls Id. Therefore Conductance;

∴Gm = Id / Vds = Id / Vgs

Thus the output resistance is;

Rout = 1 / Gm

∴Rds = 1 / [K’W(Vgs – Vt)]

Applications of Mosfet as a Current Source

  • Current source and sink are basically two terminal devices whose current at any instance of time is independent of the voltage across two terminal
  • However the current of sink and source flows from positive node through sink or source to negative node.
  • Certainly the current sink has negative node at Vss and current source has positive node at VddApplication of e mosfet as current source

Vout > Vgs – Vt

For instance, if substrate and source are connected to ground. The output resistance is;

Rout = 1 / λ Idapplication of mosfet as a current source

Vout ≤ Vgg – Vt

Current Mirror

However, the current mirror circuit uses the principle that if the gate to source voltage of two MOSFET is equal then the current flowing through the channel should be the same.current mirror circuit

Whenever M1 is in saturation region Vds1 = Vgs1

Although assuming that Vds2 > Vgs2 – Vt2 which in turn allows the M2 to be in the saturation region.

(I1/I2) = (L1W2/W1L2)(Vgs−Vt2/Vgs−Vt1)2(1+λVds2/1+λVds1)(K2/K1)

The current mirror circuit is processed on the same integrate circuit. Therefore VT and K are equal

∴(I1/I2) = (L1W2/W1L2)(1+λVds2/1+λVds1)

whenever; Vds2 = Vds1

(I1/I2) = (L1W2/W1L2)

Certainly, there are three main effects that cause the current mirror to be different from the ideal condition.

  • Firstly, Channel length modulation
  • Secondly, Threshold offset between the transistors
  • and finally, Imperfect geometrical Structure

Channel length modulation

(I1 / I2) = (1 + λVds2 / 1 + λVds1)

Rout = 1 / λ Id

Eventually, we assume that λ is the same for both the MOSFETs. Thus the difference between drain to source voltage may cause a change from the ideal unity gain condition.

Threshold offset voltage

Besides channel length modulation second non-ideal effect is the offset threshold voltage of two MOSFETs. However, assume that both the MOSFETs are identical in all aspects except Vt.

(I1 / I2) = (Vgs − Vt2 / Vgs − Vt1)

Comparatively the value of Vgs must be high enough to nullify the effect of Vt. this is for better performance.

Error in aspect ratio

Generally, to minimize the effect of this parameter the geometrical size of the device must be increased.

Advantages

  • Moreover its gain and bandwidth is quite accurate
  • besides, it is also one of the most stable devices
  • low input impedance because of this the input current becomes insensitive of o/p impedance of source.
  • High o/p impedance subsequently causes the output impedance to be insensitive load.

Disadvantages

  • Introduces Noise because of the absence of emitter resistance this can be avoided by using large emitter resistance.
  • Generally this connectivity may cause distortion in the image.

Wilson Current Mirror

Mostly Wilson current mirror circuit is known as an advance version because it has high output impedance and stability.

wilson current mirror circut

CMOS Inverter as an amplifier

CMOS inverter includes active PMOS inverter, current source inverter as well as a push-pull inverter. However, the small-signal gain of this circuit decreases from left to right in each case.

Active Load inverter

NMOS Amplifier with enhancement load

Many times low inverting stage is desired that has highly predictably small and on the other hand large-signal characteristics. Then in such cases this connection is use.

Whereas, the transistor is operating in cutoff region(V1<Vt) and the current is equal to 0 and there is no voltage drop at the output.

on the other hand when V1>Vt the transistor is on and is operating in saturation region. since Vds<Vgs-Vt

nmos active load inverter

Vds1 ≥ Vgs1 – Vt1 → Vout ≥ Vin – 0.7V

∴Ri = ∞

∴Rout = Rds1 || (1/gm2) || Rds2

Av = Vo / Vi = -gm(Rds1 || (1/gm2) || Rds2)

Certainly in the above figure of n channel Mosfet is use with gate and drain shorted. however in this type of connection the MOSFET act as an enhancement load device

Most certainly, M2 is load &mosfet M1 is a driver.

Current Source load inverter amplifier

Meanwhile, in this circuit current source is use as a load. This type of circuit mostly has common gate configurations using p-Mosfet with a gate in connection to V bias voltage. The gain of this amplifier is usually higher than the active load configuration.

Vds1 ≥ Vgs1 – Vt1 → Vout ≥ Vin – 0.7V

∴Ri = ∞

∴Rout = 1 / (gds1 + gds2 ) → 1 / Id(λ1 + λ2)

Av = Vout / Vin = -gm1 / (gds1 + gds2 )

Application of Mosfet as a Digital circuit

  • Consequently the most common application of mosfet is digital Logic gate, register or memory array.
  • for instance they are mainly used as NAND gate, nor GATE and Inverters

Mosfet as NAND Gate

CMOS NAND GATE Logic IC

The above example demonstrates the usage of MOSFET as a NAND gate. The circuit mainly consists of 2 NMOS and 2 PMOS. however here both the PMOS’s are connected in parallel whereas, both the NMOS’s are connected in series.

certainly what happens here is when any one of the applied voltages is low it results in providing a path either through PMOS1 or through PMOS 2. As both MOSFETs are in series the output gets connected to the Vdd and we get a high output.

On the other hand, if both the terminals are at low voltage results in offing both the PMOS’s. this results in no connection between the Vdd and the output. which in turn sum ups to resulting low output.

Besides all of the above, we can use inverters for making different flip flops.

Conclusion

Here we are at the last part of the blog. I hope that you liked the blog and are satisfied with the content. if you are happy then please do like and share it with others. above all please don’t forget to comment down below the part which you liked the most and also feel free to ask any doubts if you have any. Besides, I would be really to know the topic which you would like to read next on.

Have a nice day:)

Regards.

Read More

  1. Logic Families and its Features| TTL Vs CMOS
  2. What is a DC Machines?- DC Motors OR DC Generator.
  3. ALL ABOUT COMMUNICATION SYSTEM.
  4. MOSFET (Construction, Working and Characteristic)
  5. Control System(Features, Types etc)

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