ECE 3741 Experiment 9

In Experiment 9, we will be working with

pulse width modulation encoding

A PWM signsl encodes information in the

width of a train of regularly spaced square pulses

a PWM signal has many uses including

power delivery, motor control, high efficiency amplifiers, analog to digital conversion, voltage regulators

A input signal is used to modulate the

pulse width of the output PWM signal

frequency at which samples are taken is known as

sample rate

The reciprocal of the sample rate is the

sample period

duty cycle

the time that the output is high vs low within one sample period

as the input signal increases

the duty cycle increases

the higher the input amplitude

the longer the output PWM will stay high within that sampling period

a PWM signal is a form of

analog to discrete conversion (ADC)

PWM generator schematic

draw and see book

The ramp (sawtooth waveform) is used to

modulate the input signal

sawtooth waveform

linearly increases from predefined minimum value to a predefined maximum, then drops back to minimum

LM311 features a

open collector output

the LM311 ______ directly output supply voltages on its own

cannot

If the BJT is turned off by a low output

Col_out and E_out are open circuited

If the BJT is turned on by a high output

Col_out and E_out are shorted

What is the function of the pull-up resistor Rp

ensures that the Col_out terminal has the well-defined value Vs+

A class D amplifier uses

rapid on/off switching of transistors instead of a constant current bias

A class D amplifier consists of a

PWM Generator, Mosfet switching, Low Pass Filter

What are the two types of MOSFET

N-type and P-type

Switch OFF

open circuit

Switch ON

short circuit

Vgs < -1V

N: Open P:Short

Vgs = 0V

N:Open P:Open

Vgs > 1V

N:Short P:Open

Sample rate for a PWM generator is equal to

the frequency of the RAMP signal

Offset voltages are applied because

both signals will be in the positive voltage range and the comparator can operate effectively

the LED gets brighter when

the duty cycle is longer

PWMin and PWMmod are

inverse of each other

cutoff frequency (fc)

1/2piRC

A limitation of op amps is that they have

current limited outputs

a physical relay switch consists of two mechanisms

the switch itself that is opened or closed by default and a magnetic coil which generates an electromagnetic field that applies a force to the switch mechanism

a physical relay is a

current controlled switch

physical relay schematic

draw and see book

a MOSFET switch is

purely electrical

a MOSFET has 3 terminals,

gate,source and drain

The MOSFET is a

voltage controlled switch

MOSFET schematic

draw and see book

in a push button switch

switch terminals are shorted when the button is pressed and open circuit otherwise

push button schematic

draw and see book

Schmitt trigger is used for

de-bouncing a switch circuit

Schmitt trigger schematic

draw and see book

Upper threshold voltage

Vu = Vb + R1/R2 * Vs

Lower threshold voltage

Vl = Vb - R1/R2 * Vs

Write the input output behavior for a Schmitt trigger

see book

Photocell and temperature sensors are

transducers (taking environmental parameter as input and outputting another parameter as a function of the input)