# Electronic Devices and Circuits Questions and Answers – Transconductance Amplifiers

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Transconductance Amplifiers”.

1. A transconductance amplifier is also called ___________
a) current to voltage convertor
b) voltage to current convertor
c) resistor
d) inductor

Explanation: A transconductance amplifier converts an input of voltage to an output of current. It is also called a current to voltage converter or I to V converter. There is usually an additional input for a current to control the amplifier’s transconductance.

2. The transconductance of a JFET ranges from ____________
a) 100 to 500 mA/V
b) 500 to 1000 mA/V
c) 0.5 to 30 mA/V
d) above 1000 mA/V

Explanation: It is very often denoted as a conductance, gm, with a subscript, m, for mutual. Transconductance is defined as follows:
Gm = IOUT/VIN
The transconductance of a JFET ranges from 0.5 to 30 mA/V.

3. The constant-current region of a JFET lies between__________
a) Cut off and saturation
b) Cut off and pinch off
c) 0 and IDSS
d) Cut off and breakdown

Explanation: Value of drain-source voltage, VDS for breakdown with the increase in negative bias voltage is reduced simply due to the fact that gate-source voltage, VGS keeps adding to the reverse bias at the junction produced by current flow. Thus the current flow remains constant between the cut off and breakdown region of JFET.

4. The source terminal of a JEFT corresponds to ____________ of a vacuum tube
a) plate
b) cathode
c) grid
d) anode

Explanation: Electron-flow from the source terminal towards the drain terminal is influenced by an applied voltage. In vacuum tube, the source terminal of JFET corresponds to the cathode of vacuum tube.

5. The output characteristics of a JFET closely resemble the output characteristics of a __________ Valve
a) diode
b) pentode
c) triode
d) tetrode

Explanation: The pentode consists of an evacuated glass envelope containing five electrodes in this order: a cathode heated by a filament, a control grid, a screen grid, a suppressor grid, and a plate (anode).
Similar to a pentode valve, with which the junction FET greatly resembles in its operational characteristics, the simplest way of calculating stage gain is by the relationship –

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A = gfs . RL

6. If the cross-sectional area of the channel in n-channel JFET increases, the drain current__________
a) is increased
b) is decreased
c) remains the same
d) decreases exponentially then increase

Explanation: The gate source junctions are reverse biased as a result depletion regions from which extend to the bar by changing gate to source voltage; effective cross sectional area decreases with the function of the gate to source voltage. With increasing the cross section area of the channel, the drain current is increased.

7. The channel of a JFET is between the ________
a) gate and drain
b) gate and source
c) drain and source
d) input and output

Explanation: The field effect transistor is a three terminal device that is constructed with no PN-junctions within the main current carrying path between the Drain and the Source terminals. The current path between these two terminals is called the “channel” which may be made of whichever a P-type or an N-type semiconductor material.

8. A certain common-source JFET has a voltage gain of 10. If the source bypass capacitor is removed, _____________
a) the voltage gain will increase
b) transconductance will increase
c) voltage gain will decrease
d) the Q-point will shift

Explanation: In common source JFET, The main purpose of a source bypass capacitor is to provide additional gain at AC. Here, the common-source JFET has a voltage gain of 10; which includes the additional AC gain provided. If the source bypass capacitor is removed, then the voltage gain will eventually decrease.

9. At cut-off, the JFET channel is ___________
a) at its widest point
b) completely closed by the depletion region
c) extremely narrow
d) reverse baised

Explanation: At cut off, the JFET channel is completely isolated by the depletion region. Gate connection is completely isolated from the main current carrying channel. At cut-off, VGS is sufficient to cause the JFET to act as an open circuit as the channel resistance is at maximum.

10. MOSFET from a JFET differs mainly because _____________
a) of power rating
b) of the output
c) the JFET has a pn junction
d) the MOSFET has two gates

Explanation: A MOSFET has no pn junction, instead at the gate of the constituent there is an insulated silicon dioxide layer that insulates from the channel. A JFET is a depletion mode transistor. A JFET has diode junction between the gate and the channel.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

To practice all areas of Electronic Devices and Circuits, here is complete set of 1000+ Multiple Choice Questions and Answers.