E&tc

1. Unit 06: Converters & PLL
Unit 01, Module 01
Matoshri College of Engineering and Research
Centre, Nashik
1
 M1: Voltage to Current, Current to Voltage converters,
Introduction to ADC and DAC.
 M2: DAC: Resistor weighted and R-2R DAC;
Characteristics, block diagrams, Circuits, Specifications,
Merits, Demerits, Comparisons.
 M3: ADC: SAR, Flash and dual slope ADC Type
Characteristics, block diagrams, Circuits, Specifications,
Merits, Demerits, Comparisons.
 M4: PLL: Block Diagram, Characteristics, phase detectors,
Details of PLL IC 565 Applications, Typical circuits.

2. Voltage to Current converter,
Unit 01, Module 01
Matoshri College of Engineering and Research
Centre, Nashik
2
 Sometimes it is essential to create
current which is proportional or
corresponding to the voltage.
 Floating Load
 Ground Load

3. Voltage to Current converter,
• .
• VD=0;
• .
• .

4. Voltage to Current converter,
• .
• .
• .
• .
• .
• .
• .
• .
• .
• .
• .
• ..

5. Current to Voltage converter
Unit 01, Module 01
Matoshri College of Engineering and Research
Centre, Nashik
5
 A current to voltage converter or I to V converter is an
electronic circuit that takes current as the input and
produces voltage as the output.

6. What is a DAC?
A digital to analog converter (DAC) is a device that converts
digital numbers (binary) into an analog voltage or current
output.

7. Principal components of DAC

8. What is a DAC?
• Digital to Analog
• Each binary number sampled by the DAC
corresponds to a different output level.
l
na
Si
g t
Outpu
og
al
An
0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011
Digital Input Signal
Analog
Output
Signal
0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011
Digital Input Signal

9. Types of DACs
• Many types of DACs available.
• Usually switches, resistors, and op- amps
used to implement conversion
• Two Types:
• Binary Weighted Resistor
• R-2R Ladder

10. Binary Weighted Resistor
• Utilizes a summing op-amp circuit
• Weighted resistors are used to distinguish each
bit from the most significant to the least
significant
• Transistors are used to switch between Vref and
ground (bit high or low)

11. Binary Weighted Resistor
Assume Ideal Op-
amp
No current into op-
amp
Virtual ground at
inverting input
Vout= -IRf
-
+
R
2R
4R
2n-1R
Rf
Vout
I
Vref

12. Binary Weighted Resistor






n-1
Vn
V

V2

V3
1
V  IRf  Rf
out
2 R
R 2R 4R

MSB
LSB
1 n
Voltages V through V are either
Vref if corresponding bit is high or
ground if corresponding bit is low
V1 is most significantbit
Vn is least significant bit
I
-
+
2n-1R
Rf
Vout
Vref
V1
V2
V
R
2R
3 4R
Vn

13. Binary Weighted Resistor
Advantages
◦ Simple
◦ Fast
Disadvantages
◦ Need large range of resistor values
(2048:1 for 12-bit) with high precision in
low resistor values
◦ Need very small switch resistances
◦ Op-amp may have trouble producing low
currents at the low range of a high
precision DAC

14. R-2R Ladder
Each bit corresponds to a switch:
◦ If the bit is high, the corresponding switch is connected
to the inverting input of the op-amp.
◦ If the bit is low, the corresponding switch is connected
to ground.

15. R-2R Ladder
B2
B1
B0

16. R-2R Ladder
Circuit may be
analyzed using
Thevenin’s
theorem (replace
network with
equivalent
voltage source
and resistance)
out ref
R 2ni
i0
V  V
Rf

n1
Bi
B2
B1
B0
Rf
R B
f
R
n1
i
2(n1)i
Vout  Vref 
i0

17. R-2R Ladder
Advantages:
◦ Only 2 resistor values
◦ Lower precision resistors acceptable
Disadvantages
◦ Slower conversion rate

18. DAC Specifications:
Reference Voltages
Resolution
Speed
Settling Time
Linearity

19. Reference Voltage
Internal vs. External Vref?
Internal External
•Non-Multiplier DAC
•Vref fixed by manufacturer
•Qualified for specified
temperature range
•Multiplying DAC
•Vary Vref
•Consider current required
•Consider Voltage range
•Consider dynamic effects
of inner structure

20. Resolution
1 LSB (digital)=1 step size for DAC output (analog)
Increasing the number of bits results in a finer resolution
Most DAC - 8 to 16-bits (256 to 65,536 steps)
e.g. 5Vref DAC
1LSB=5/28 =0.0195V resolution(8-bit)
1LSB=5/23 =0.625V resolution(3-bit)
2n
Resolution 
Vref
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
8-bit Resolution
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
3-bit Resolution
1
LSB

21. Speed (Max. Sampling Frequency)
The maximum rate at which DAC is reproducing usable
analog output from digital input register
Digital input signal that fluctuates at/ has high frequency
require high conversion speed
Speed is limited by the clock speed of the microcontroller
(input clock speed) and the settling time of the DAC
E.g. To reproduce audio signal up to 20kHz, standard CD
samples audio at 44.1kHz with DAC ≥40kHz
Typical computer sound cards 48kHz sampling freq
>1MHz for High Speed DACs

22. Settling Time
The interval between a command to update (change) its
output value and the instant it reaches its final value,
within a specified percentage (± ½ LSB)
Ideal DAC output would be sequence of impulses 
Instantaneous update
Causes:
◦ Slew rate of output amplifier
◦ Amount of amplifier ringing and signal overshoot
Faster DACs have shorter settling time
Electronic switching  fast
Amplifier settling time  dominant effect

23. Settling Time
tsettle

24. DAC Linearity
The difference between the desired analog output and the actual
output over the full range of expected values
Does the DAC analog output vary linearly with digital input signal?
Can the DAC behavior follow a constant Transfer Function
relationship?
Ideally, proportionality constant – linear slope
Increase in input  increase in output  monotonic
Integral non-linearity (INL) & Differential non-linearity (DNL)
l
a
n
g
Si
t
tp
u
O
u
lo
g
a
An
0000 0001 0010 0011 0100 0101
Digital Input Signal
0000 0001 0010 0011 0100 0101
0101
0100
0001
0000
Analog
Output
Signal
l
a
n
g
Si
t
tp
u
O
u
lo
g
a
An
0000 0001 0010 0011 0100 0101
Digital Input Signal
0000 0001 0010 0011 0100 0101
0101
0100
0001
0000 0010 0011
Digital Input Signal
Analog
Output
Signal
0010 0011
Digital Input Signal
Linear Non-Linear

25. Common Applications:
Function Generators
Digital
Oscilloscopes
◦ Digital Input
◦ Analog Ouput
Signal Generators
◦ Triangle wave generation
◦ Sine wave generation
◦ Square wave generation
◦ Random noise generation
1
2

26. CommonApplications
Used when a continuous analog signal is
required.
Signal from DAC can be smoothed by a
Low pass filter
0 bit
nth bit
n bit DAC
011010010101010100101
101010101011111100101
000010101010111110011
010101010101010101010
111010101011110011000
100101010101010001111
Digital Input
Filter
Piece-wise
Continuous Output
Analog
Continuous Output

27. Applications – Video
Video signals from digital sources, such as a
computer or DVD must be converted to analog
signals before being displayed on an analog
monitor. Beginning on February 18th, 2009 all
television broadcasts in the United States will
be in a digital format, requiring ATSC tuners
(either internal or set-top box) to convert the
signal to analog.

28. Analog to Digital Converter(ADC )
Unit 01, Module 01
Matoshri College of Engineering and Research
Centre, Nashik
28
 It is a system that converts an analog signal, (such
as a sound picked up by a microphone or light
entering a digital camera), into a digital signal.
 Successive Approximation (SAR) ADC
 Dual Slope ADC.
 Flash ADC.
 Pipelined ADC.
 Delta-sigma (ΔΣ) ADC


29. Analog-to-Digital Conversion
 Terminology
 Analog: continuously valued signal, such as
temperature or speed, with infinite possible values
in between
 Digital: discretely valued signal, such as integers,
encoded in binary
 Analog-to-digital converter: ADC, A/D, A2D;
converts an analog signal to a digital signal

30. Analog Signals
Analog signals –directly measurable quantities
in terms of some other quantity
Examples:
• Thermometer –mercury height rises as
temperature rises
• Car Speedometer –Needle moves farther
right as you accelerate

31. Digital Signals
Digital Signals –have only two states. For
digital computers, we refer to binary states, 0
and 1. “1” canbe on, “0”canbe off.
Examples:
• Light switch can be either on or off
• Door to a room is either open or closed

32. ADC Basic
Principle:
• The basic principle of operation is to use
the comparator principle to determine
whether or not to turn on a particular bit of
the binary number output.
• It is typical for an ADC to use a digital-
to- analog converter (DAC) to
determine one of the inputs to the
comparator.

33. ©Alex Doboli
2006
Quantization
•Quantization is the process of converting the sampled continuous-
Valued signals into discrete-valued data

34. Quantizing
The number of possible states that
the converter can output is:
N=2n
where n is the number of bits in the
AD converter
Example: For a 3 bit A/D converter,
N=23=8.
Analog quantization size:
Q=(V max -V min)/N = (10V – 0V)/8 = 1.25V

35. Analog  Digital Conversion
2-Step Process:
• Quantizing - breaking down analog value
is a set of finite states
• Encoding - assigning a digital word or
number to each state and matching it to the
input signal

36. Step 1:
Quantizing
Example:
You have 0-10V
signals. Separate
them into a set of
discrete states with
1.25V increments.
(Ho
w did we get 1.25V?
(Discussed in previous
slide)
Output
States
Discrete Voltage
Ranges (V)
0 0.00-1.25
1 1.25-2.50
2 2.50-3.75
3 3.75-5.00
4 5.00-6.25
5 6.25-7.50
6 7.50-8.75
7 8.75-10.0

37. Step 2.
Encoding
• Here we assign the
digital value (binary
number) to each
state for the
computer to read.
Output
States
Output Binary Equivalent
0 000
1 001
2 010
3 011
4 100
5 101
6 110
7 111

38. ADC Basic Principle:
• The basic principle of operation is to use the
comparator principle to determine whether or
not to turn on a particular bit of the binary
number output.
• It is typical for an ADC to use a digital-to-
analog converter (DAC) to determine one of
the inputs to the comparator.

39. Elements of the Successive Approximation ADC
Successive Approximation Register
Digital to Analog Converter
Takes in a Combination of Bits

40. Successive Approximation (SAR) ADC
Unit 01, Module 01
Matoshri College of Engineering and Research
Centre, Nashik
40

41. Successive approximation
ADC
• Much faster than the digital ramp ADC
because it uses digital logic to converge
on the value closest to the input voltage.
• A comparator and a DAC are used in
the process.

42. Successive Approximation
ADC
• A Successive Approximation Register
(SAR) is added to the circuit
• Instead of counting up in binary sequence,
this register counts by trying all values of
bits starting with the MSB and finishing at
the LSB.
• The register monitors the comparators
output to see if the binary count is greater
or less than the analog signal input and
adjusts the bits accordingly

43. Successive Approximation
ADC Circuit

44. Elements of a Flash A/D Converter
Encoder
Comparator

45. FLASH A/D CONVERTER
3 Bit Digital Output
Resolution
23-1 = 7 Comparators

46. 3 Bit-FLASH A/D CONVERTER

47. Flash A/D Converter Contd.
 Pros
 Fastest (in the order of
nano seconds)
 Simple operational
theory
 Speed is limited only by
gate and comparator
propagation delay
Cons
• Each additional bit of
resolution requires twice
the number of
comparators
• Expensive
• Prone to produce
glitches in the output

48. Dual-Slope ADC
*

49. Dual-Slope ADC

50. Dual Slope A/D Converter Contd.
Pros
• High accuracy
•Fewer adverse
affects from noise
Cons
• Slow
•Accuracy is
dependent on the
use of precision
external
components

51. What is Phase Locked Loop
(PLL)
PLL is an Electronic Module (Circuit) that
locks the phase of the output to the input.
A PLL is a negative feedback system where an
oscillator-generated signal is phase and
frequency locked to a reference signal.

52. Parts of a PLL
• Phase Detector
• Filter
• Voltage Controlled Oscillator

53. Parts of a PLL
● Phase Detector
• Acts as comparator
• Produces a voltage proportional to the phase difference
between input and output signal
• Voltage becomes a control signal

54. Implementation of PD
●
Phase Detector is an XOR gate.

55. Implementation of PD

56. Parts of a PLL
● Filter
• Determines dynamic characteristics of PLL
• Specify Capture Range (bandwidth)
• Specify Tracking Range
• Receives signal from Phase Detector and filters accordingly

57. Parts of a PLL
● Voltage Controlled Oscillator
• Set tuning range
• Set noise margin
• Creates low noise clock oscillation

58. Block Diagram of IC565 PLL

59. Lock range and capture range, Free
Running Frequency of VCO