DIGITAL TO ANALOG CONVERSION
Digital Signal – A signal that
represents data as a sequence of discrete values at any given time.
Analog Signal – Continuous signal for which the time-varying feature of the signal.
INTRODUCTION OF DIGITAL TO ANALOG CONVERSION
· Digital-to-analog conversion (DAC) is a fundamental process in Data Communication Networks (DCN)
for converting digital signals to analog signals such as telephone lines, radio
frequencies, or cable TV lines.
· DAC translating
discrete digital values into continuous analog signals that vary in amplitude
or frequency.
· DAC used in various
applications including Modems, Wireless Communication, Voice over IP (VoIP ) Remote
Sensing and Telemetry, and Control Systems.
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FEATURES
Some key features:
1. Resolution: the number of bits
used to represent the analog output.
2. Sampling Rate: how frequently
the digital input signal is sampled and converted into analog form.
3. Accuracy: how closely the analog output matches the
original digital signal.
4. Linearity: how faithfully the DAC converts digital
values to analog voltages across its entire range.
5. Noise
Performance: low noise levels to ensure that unwanted
noise does not degrade the quality of the analog signal.
6. Dynamic Range: the ratio between
the maximum and minimum levels of the analog signal it can produce.
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ADVANTAGES
Some key
advantages are:
1.
Interoperability:
between digital and analog communication systems.
2. Efficient
Transmission:
more cost-effective or readily available in certain situations.
3. Integration
with Existing Infrastructure: without the need for extensive
infrastructure upgrades or replacements.
4. Noise
Resilience: reducing
the impact of noise and ensuring reliable communication.
5. Flexibility: encoding
digital data into analog signals, allowing adaptation to different
communication environments and requirements.
6. Support for
Voice and Multimedia:
the transmission of voice, audio, video, and multimedia data over analog
communication channels.
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DRAWBACKS
Certain drawbacks
and challenges are:
1. Loss of
Information:
loss can result in degradation of signal quality and affect the accuracy of the
transmitted data.
2. Noise and
Interference:
distortion during transmission, leading to potential errors in the received
data.
3. Complexity of
Circuitry:
Increases the cost of hardware implementation and maintenance.
4. Limited
Bandwidth:
restrict the data rate and transmission capacity of analog communication
systems.
5. Signal
Degradation over Distance: leading to potential errors or loss of data
integrity.
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USAGES OR
APPLICATIONS
Some of the key
usages or applications are:
1. Modems:
2. Voice over IP
(VoIP):
3. Analog
Transmission:
4. Wireless
Communication:
5. Control
Systems:
6. Remote Sensing
and Telemetry:
7. Data
Transmission over Power Lines:
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TECHNIQUES OF DIGITAL TO ANALOG CONVERSION
Several techniques
are employed for this purpose, each offering different advantages and suitable
for specific applications:
1. Pulse Amplitude Modulation (PAM)/Amplitude Shift Keying (ASK):–
Amplitude Shift
Keying is a technique in which the carrier signal is analog and the data to be
modulated is digital.
The amplitude of the analog carrier signal is modified to reflect binary data.
The binary signal
when modulated gives a zero value when the binary data represents 0 while giving
the carrier output when the data is 1.
The frequency and
phase of the carrier signal remain constant.
In PAM, the
amplitude of a series of pulses is varied according to the amplitude of the
analog signal being encoded. a simple form of modulation that can be implemented
using basic electronic components.
FIGURES FROM WEB RESOURCE
1. Amplitude
Encoding:
2. Simple
Implementation:
3. Bandwidth
Efficiency:
4. Low Complexity:
--------------------------
Advantages:
1. Simplicity:
2. Efficiency:
3. Compatibility:
4. Flexibility:
5. Transmit
digital data over optical fiber.
6. Inexpensive: - The
receiver and transmitter have a simple design.
7. High bandwidth efficiency:
- Use lesser bandwidth as compared to FSK
---------------------
DRAWBACKS:
1. Susceptibility
to Noise:
2. Limited
Signal-to-Noise Ratio (SNR):
3. Bandwidth
Limitations:
4. Limited Data
Rate:
5. Susceptible to
noise interference:- entire transmissions could be lost.
6. lower power
efficiency:
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USAGES
1. Modems:
2. Audio
Transmission:
3.
Analog-to-Digital Conversion:
4. Power Line
Communication (PLC):
--------------------------
2. Pulse Width Modulation (PWM) or Frequency Shift Keying:
Converting digital
signals into analog signals for transmission over analog communication channels
or for controlling analog devices.
The frequency of
the analog carrier signal is modified to reflect binary data.
This technique
uses two frequencies, f1 and f2. f1 is chosen to represent binary digit 1 and f2
is used to represent binary digit 0.
In this modulation, the frequency of the analog carrier signal is modified to reflect binary data.
The output of a
frequency shift keying modulated wave is high in frequency for a binary high
input and is low in frequency for a binary low input. The amplitude and phase
of the carrier signal remain constant.
FIGURES FROM WEB RESOURCE
Features:
1. Variable Pulse
Width:
2. Fixed
Frequency:
3. Duty Cycle:
Advantages:
1. Simple Implementation
2.
Efficiency:
3.
Analog
Signal Accuracy:
4.
Noise
Immunity:
5.
Digital
Compatibility:
6.
Lower
chances of an error.
7.
High
signal-to-noise ratio.
8.
Simple
implementations for low data rate applications.
Drawbacks:
1.
Resolution
Limitations:
2.
Harmonic
Distortion:
3.
Sensitivity
to Timing Variations:
4.
Larger
bandwidth as compared to ASK
5.
Less
bandwidth efficiency.
6.
Lower
power efficiency.
Usages:
1. Modems:
2. Power Control:
3. Analog Audio
Transmission:
4. Lighting
Control:
5. Temperature
Control:
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3. Pulse Position Modulation (PPM):
Transmit digital
data over analog communication channels.
The timing of the
transmitted pulses is varied based on the digital data being encoded.
Each pulse
represents a specific information element, and its position within a fixed time
interval carries the digital information.
When a new binary
symbol is encountered, the phase of the signal is altered.
The amplitude and
frequency of the original carrier signal are kept intact.
In this modulation, the phase of the analog carrier signal is modified to reflect binary data.
The amplitude and
frequency of the carrier signal remain constant.
Features:
1. Timing-based
Encoding:
2. Simple
Implementation:
3. Resistance to
Amplitude Variations:
Advantages:
1.
Resilience
to Amplitude Variations:
2.
Efficient
Use of Bandwidth:
3.
Simple
Implementation:
4.
Low
Power Consumption:
5.
Communication
signal is much more efficient as compared to FSK.
Drawbacks
1.
Sensitive
to Timing Errors:
2.
Limited
Signal-to-Noise Ratio (SNR) Performance:
3.
Lower
Spectral Efficiency:
4.
Low
bandwidth efficiency.
5.
The
detection and recovery algorithms of binary data is very complex.
6.
A
non-coherent reference signal.
It is further
categorized as follows:
Binary Phase Shift
Keying (BPSK):
· BPSK also known as
phase reversal keying or 2PSK is the simplest form of phase shift keying.
· The Phase of the
carrier wave is changed according to the two binary inputs.
· Difference of 180
phase shift is used between binary 1 and binary 0.
· Most robust
digital modulation technique and is used for long-distance wireless
communication.
Quadrature Phase
Shift Keying
· This technique is
used to increase the bit rate i.e. we can code two bits onto one single element.
· It uses four
phases to encode two bits per symbol.
· QPSK uses phase
shifts of multiples of 90 degrees.
·
It
has double data rate carrying capacity compared to BPSK as two bits are mapped
on each constellation point.
· QPSK alters the
phase to reflect two binary digits at once.
· The mainstream of
binary data is divided equally into two sub-streams.
· The serial data is
converted into parallel in both sub-streams and then each stream is converted
to a digital signal using the NRZ technique.
Usages:
1. Wireless
Communication:
2. Optical
Communication:
3. Data
Transmission over Noisy Channels:
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Other techniques:-
Delta-Sigma Modulation
(ΔΣ):
- ΔΣ modulation is a technique that
oversamples the digital signal and uses feedback to quantize the difference
between the analog output and the desired signal.
Digital-to-Analog Converter (DAC) Chips:
- DAC chips are integrated circuits designed
specifically for converting digital signals into analog signals.
- DAC chips are widely used in DCN for their
high precision, accuracy, and flexibility.
Hybrid Methods:
- Some DAC implementations in DCN may
combine multiple techniques to achieve the desired performance characteristics.
- For example, a hybrid DAC may use PWM for
coarse resolution and switch to delta-sigma modulation for finer resolution at
lower amplitudes.
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