EGR220 Than & Bhavin Lab #2

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Introduction and Objectives

Diodes are non-linear devices and there are many non-

linear circuit applications of diodes. However, limiter

circuits, which involve diodes, can act as a linear

circuit for a certain range. Therefore, in this lab, we

were instructed to measure and analyze transfer

characteristic of limiter circuits. The primary

objectives of this lab are:

1. To analyze and understand the nature of

limiter circuits and clipping

2. To understand about transfer characteristic of

limiter circuit

3. To be able to approximate the transfer

characteristic of limiter circuit with ideal and

constant voltage drop model.

4. To be able to capture the transfer functions of

limiter circuit

Equipments and Components used

In this lab, the equipments and components we used

are:- diodes: 1N914 (x2); resistors: 10KΩ @ 1W (or

more) (x2); a breadboard, a waveform generator,

±20V power supply, a multi-meter, an Oscilloscope to

capture the I-V curve, wires and cords.

Procedures

Procedure 1: Analyzing Transfer Functions of

Half-Wave Rectifier Circuits

Figure 1

In order to capture the transfer function on

Oscilloscope, we used time varying voltage source

( ±10V Sine Wave with frequency of 1kHz). One

oscilloscope probe was directly connect to the voltage

source and the other was placed across the diode to

measure diode voltage. We, then, captured the

oscilloscope images of the both Vi and Vo.

Figure 2: 2 Waveforms of Vi (10Vpp) and Vo

Figure 3: Transfer Function of Vi and Vo

By moving the cursor, we figured out the

maximum and minimum Vo . We found that the

maximum output voltage is nearly zero and the

minimum output voltage is almost -10.0V and the

maximum current is 1 mA, and Vpp for output voltage

is 10V. Our findings were agreed with our calculations

based on Ideal Model. In oder to calculate the

conduction angle, we solved for θ from the following

equation:

10 Sin (θ) = 0 (1)

θ = 0 or θ = π. Δθ = π; therefore, half cycle of the

input waveform. We could also see that effect on

transfer function image, in which the slanted line

EGR220 Than & Bhavin Lab #2

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represents the half of waveform.

In oder to understand the effect of changing amplitude

of input voltage, we again used the ±8V Sine Wave

with frequency of 1kHz for input voltage, and captured

the oscilloscope images.

Figure 4: 2 Waveforms of Vi (8 Vpp) and Vo

Figure 5: Transfer Function of Vi (8 Vpp) and Vo

From our measurement, we found that the minimum

output voltage of the limiter circuit became smaller as

the input voltage became smaller.

Figure 5: Transfer Function of Vi (8 Vpp) and Vo

(Opposite Polarity of Diode in Circuit 1)

We also found that when we changed the polarity of

the diode, the minimum and maximum output voltage

became 0V and +8V. We could make a conclusion that

we could change the polarity and amplitude of transfer

function by changing the polarity of diode in the

limiter circuit and input voltage source.

Procedure 2: Analyzing Transfer Functions of

Double- Limiter Circuits

Figure 6

We built the circuit as shown in figure 6, and captured

the oscilloscope image of the transfer function. From

our pre-lab, calculation we estimated that the max and

min of output voltage would be ±5V (~6.5V) , since

the diode can give linearity between 0 and 0.65V .

Figure 7: 2 Waveforms of Vi (10Vpp) and Vo

n oder to calculate the conduction angle, we solved for

θ from the following equation:

EGR220 Than & Bhavin Lab #2

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10 Sin (θ1) = 5 (2)

10 Sin (θ2) = -5 (3)

θ1 = π/6 or θ1 = 5π/6. Δθ1 = 4π/6; θ2 = -π/6 or θ2 = -

5π/6. Δθ2 = -4π/6.

Figure 8: Transfer Function of Vi (10 Vpp) and Vo

From the screen image, we could see that the

saturation range would be between π/6 and 5π/6, -π/6

and -5π/6.

Procedure 3: Analyzing Transfer Functions of

Limiter Circuits with DC Components

Figure 9

By using Ideal Model, we got [1]:

Vo = Vi Vi < 1.5

Vo = ½ Vi 1.5 < Vi < 3

Vo = 0 Vi > 3

By using constant voltage drop Model [1], we got:

Vo = Vi Vi < 2.2

Vo = 1/2Vi 2.2 < Vi < 3.7

Vo = 0 Vi > 3.7

When we captured the screen image of transfer

function of the circuit in figure 9, we got the following

image.

From the screen image, we found that there are 3

regions corresponding to the 3 stages of the output

voltage.

By moving cursors, we found that the first voltage

range in the transfer function is almost +2.5V, the

second range is between 2.5V and 3.7V, and the third

range is over 3.7V.

Discussion

Limiters have many uses in signal processing systems.

Depending on the polarity and existence of DC

components, we are able to change the linear range,

threshold value and saturation range of limiters. The

half-wave rectifier circuits can provide piece-wise

linear transfer function, which has a slope that equals

to ratio of Vo and Vi. Double limiter circuits have

linear transfer function with a certain saturation range.

And finally, saturation range of the limiter circuit could

be changed by adding DC components to the limiter

circuits.

References [1] Sedra, Adel S., and Smith. Kenneth C. “Microelectronics

Circuits”. 5th. New York: Oxford University Press, 2004.