ELECTRONIC DEVICES NINTH EDITION FLOYD, Assignments of Electronics

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© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

Electronic Devices

Ninth Edition

Floyd

Chapter 9

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Common-Source Amplifier

The voltage gain is given by the equation Av = gmRd.

In a CS amplifier, the input

signal is applied to the gate

and the output signal is taken

from the drain. The amplifier

has higher input resistance

and lower gain than the

equivalent CE amplifier.

RL Vout R D

• V DD C 3 Vin R G C 1 R S C 2

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Common-Source Amplifier

You can estimate what the transfer characteristic looks like from values on the specification sheet, but keep in mind that large variations are common with JFETs. For example, the range of specified values for a 2N5458 is shown. –7 –1 0 9 I D (mA)

• V GS (V) 2 Gate-Source Cutoff Voltage (VDS = 15 Vdc, i (^) D = 10 nAdc) Zero Gate-Source Drain Current (VDS = 15 Vdc, VGS = 0) OFF CHARACTERISTICS ON CHARACTERISTICS 2N 2N 2N 2N V (^) GS(off) I (^) DSS -0.5 - -6.0 Vdc 1.0 3.0 5.0 mAdc -1.0 - -7. 2.0 6.0 9. Symbol Min Typ Max Unit Symbol Min Typ Max Unit

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Common-Source Amplifier

To analyze the CS amplifier. you need to start with dc values. It is useful to estimate I D based on typical values; specific circuits will vary from this estimate. For a typical 2N5458, what is the drain current? From the specification sheet, the typical I DSS = 6.0 mA and VGS(off) = 4 V. These values can be plotted along with the load line to obtain a graphical solution. V DD +12 V R D 2.7 kW R S 470 W C 2 10 mF Vin 100 mV R G 10 MW Vout 0.1 mF C 1 2N See the following slide…

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Common-Source Amplifier

Alternatively, you can obtain I D using Equation 9-2: 2 D S D DSS GS(off) 1 I R I I V    (^)        The solution to this quadratic equation is simplified using a calculator that can handle quadratic equations. ID=IDSS (1–( ID RS/VG...– ID= IDSS= RS= VGSOFF= bound=(–1 99,1 99)E E GRAPH RANGE ZOOM TRACE SOLVE After entering the equation, enter the known values, but leave I D open. For the typical values for the 2N5458, ( I DSS = 6 mA and VGS(off) = 4 V) with a source resistance of 470 W, we find 2.75 mA. **. 470

.** F (continued) enter absolute value press

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Common-Source Amplifier

Assume I DSS is 6.0 mA, V GS(off) is 4 V, and V GS = 1.3 V as found previously. What is the expected gain?

DSS^ ^ 

0 GS(off) 2 2 6.0 mA 3.0 mS 4 V m I g V    GS 0 GS(off) 1 1.3 V 3.0 mS 1 4.0 V 2.02 mS m m V g g V    (^)            (^)       V DD +12 V R D 2.7 kW R S 470 W C 2 10 mF Vin 100 mV R G 10 MW Vout 0.1 mF C 1 2N Av = gmRd = (2.02 mS)(2.7 kW) = 5. Output is inverted

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The D-MOSFET

In operation, the D-MOSFET has the unique property in that it can be operated with zero bias, allowing the signal to swing above and below ground. This means that it can operate in either D-mode or E-mode. Vout R D

• V DD C 2 RL Vin R G C 1 Q I D

• V GS^0 + V GS Id Vgs

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The E-MOSFET

The E-MOSFET is a normally off device. The n -channel device is biased on by making the gate positive with respect to the source. A voltage-divider biased E-MOSFET amplifier is shown. Vout R D

• V DD RL Vin R 2 R S^ C^2 R 1 C 3 C 1 0 V GS(th) I DQ V GS Enhancement Q V GSQ I D Id Vgs

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Common-Drain Amplifier

The voltage gain is given by the equation

In a CD amplifier, the input

signal is applied to the gate

and the output signal is taken

from the source. There is no

drain resistor, because it is

common to the input and

output signals.

• V DD Vin Vout R G R S RL C 2 C 1 1 m s v m s g R A g R

The voltage gain is always < 1, but the power gain is not.

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Cascode Amplifier

The cascode connection is

a combination of CS and

CG amplifiers. This forms

a good high-frequency

amplifier. The input and

output signals at 10 MHz

are shown for this circuit

on the following slide…

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Class-D Amplifier

MOSFETs are useful as class-D amplifiers, which are very efficient because they operate as switching amplifiers. They use pulse width modulation, a process in which the input signal is converted to a series of pulses. The pulse width varies proportionally to the amplitude of the input signal. Pulse-width modulation is easy to set up in Multisim. The following slide shows the circuit. A sine wave is compared to a faster triangle wave of the about the same amplitude using a comparator (a 741 op-amp can be used at low frequencies).

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Class-D Amplifier

A circuit that you can use in lab or in Multisim to observe pulse width modulation in action. The scope display is shown on the following slide… Op-amp set up as a comparator

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Class-D Amplifier

Q 1 Q 2 R L

• V DD

• V DD Low-pass filter Modulated input The modulated signal is amplified by class-B complementary MOSFET transistors. The output is filtered by a low-pass filter to recover the original signal and remove the higher modulation frequency. PWM is also useful in control applications such as motor controllers. MOSFETs are widely used in these applications because of fast switching time and low on- state resistance.

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition

The Analog Switch

MOSFETs are also used as analog switches to connect or disconnect an analog signal. Analog switches are available in IC form – for example the CD4066 is a quad analog switch that used parallel n - and p -channel MOSFETs. The configuration shown allows signals to be passed in either direction. Advantages of MOSFETs are that they have relatively low on-state resistance and they can be used at high frequencies, such as found in video applications. Simplified internal construction of a bidirectional IC analog switch. Control IN/OUT OUT/IN