ec2357 lab manual
TRANSCRIPT
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Contents
1 Current-Controlled Ring Oscillators 7
1 Duration : 2 weeks . . . . . . . . . . . . . . . . . . . . . . . . 72 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Laboratory Work . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Switching Noise Injector . . . . . . . . . . . . . . . . . 9
3.3 Simulation and Analysis . . . . . . . . . . . . . . . . . 9
4 Laboratory Report . . . . . . . . . . . . . . . . . . . . . . . . 10
2 D-flipflop Phase/Frequency Detectors 13
1 Duration : 2 weeks . . . . . . . . . . . . . . . . . . . . . . . . 132 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3 Laboratory Work . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1 D-Flipflops . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2 D-Flipflops with RESET . . . . . . . . . . . . . . . . . 14
3.3 AND2 Gate . . . . . . . . . . . . . . . . . . . . . . . . 14
3.4 D-flipflop Phase/Frequency Detector . . . . . . . . . . 15
4 Laboratory Report . . . . . . . . . . . . . . . . . . . . . . . . 16
3 Phase-Locked Loops 191 Duration: 2 weeks . . . . . . . . . . . . . . . . . . . . . . . . . 19
2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3 Laboratory Work . . . . . . . . . . . . . . . . . . . . . . . . . 20
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3.1 Charge Pumps . . . . . . . . . . . . . . . . . . . . . . 20
3.2 Loop Filters . . . . . . . . . . . . . . . . . . . . . . . . 223.3 Open-Loop Test . . . . . . . . . . . . . . . . . . . . . . 22
3.4 Closed-Loop Test . . . . . . . . . . . . . . . . . . . . . 23
4 Laboratory Report . . . . . . . . . . . . . . . . . . . . . . . . 24
4 Phase-Locked Loop Chip Set 27
1 Duration : 4 weeks . . . . . . . . . . . . . . . . . . . . . . . . 27
2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3 Models for Packaging . . . . . . . . . . . . . . . . . . . . . . . 27
4 Models for Bond Pads . . . . . . . . . . . . . . . . . . . . . . 285 Models for Bond Wires . . . . . . . . . . . . . . . . . . . . . . 29
6 Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7 Laboratory Work . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.1 Complete Test Circuit Construction . . . . . . . . . . . 29
7.2 VDD and VSSPads . . . . . . . . . . . . . . . . . . . . 30
7.3 VCO Output Buffering . . . . . . . . . . . . . . . . . . 31
7.4 PLL Test . . . . . . . . . . . . . . . . . . . . . . . . . 31
8 Layout of PLL . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.1 Floor-Planning of PLL . . . . . . . . . . . . . . . . . . 328.2 Layout of PLL . . . . . . . . . . . . . . . . . . . . . . 32
8.3 I/O Pin Assignment . . . . . . . . . . . . . . . . . . . 33
8.4 Layout of Pads . . . . . . . . . . . . . . . . . . . . . . 33
8.5 Layout of Output Buffers . . . . . . . . . . . . . . . . 33
9 Laboratory Report . . . . . . . . . . . . . . . . . . . . . . . . 34
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List of Figures
1.1 Four-stage fully differential current-controlled ring oscillator . 9
1.2 Symbol of the delay cell of fully differential current-controlled
ring oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1 D flip-flop phase/frequency detector. . . . . . . . . . . . . . . 15
2.2 D flip-flops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1 Basic configuration of type II phase-locked loops. . . . . . . . 20
3.2 Current-steering charge pump. The charge pump conveysJUP
to the downstream loop filter when UP=1 and DN=0. It sinks
JDN from the loop filter when DN=1 and UP=0. . . . . . . . 21
3.3 Implementation of the current-steering charge pump. . . . . . 223.4 Open-loop test circuit. . . . . . . . . . . . . . . . . . . . . . . 23
3.5 Fully differential cross-coupled voltage-controlled oscillator. . . 24
4.1 Simplified schematic of complete chip set . . . . . . . . . . . . 30
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List of Tables
4.1 Pad assignment of phase-locked loop chip set. . . . . . . . . . 31
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Chapter 1
Current-Controlled Ring
Oscillators
1 Duration : 2 weeks
2 Introduction
Voltage (current)-controlled ring oscillators are used extensively in computer
systems and data communication networks. This laboratory investigates the
design of fully differential CMOS current-controlled ring oscillators with an
emphasis on switching noise and their impact on the timing jitter of the os-
cillators. In this laboratory, you are required to design a four-stage fully dif-
ferential CMOS current-controlled ring oscillator using TSMC-0.18m 1.8V
CMOS technology and analyze the performance of the designed oscillator
using Spectre from Cadence Design Systems with BSIM3.3v device models.
The oscillation frequency of the oscillator is 900 MHz. The delay cell of the
oscillator was the originally reported in [1], as shown in Fig.1.1. This delay
cell utilizes a positive latch formed by M12 to combat the switching noise
present on the power and ground rails in the following ways : (i) The positive
feedback reduces the transition time and sharpens both the rising and falling
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CHAPTER 1. CURRENT-CONTROLLED RING OSCILLATORS 8
edges of the waveform of the oscillator. (ii) A fast transition minimizes the
timing jitter of the oscillator. As pointed out in [2] the noise of the MOS de-vices and the switching noise of the VCOs output at the threshold-crossing
shifts the actual threshold-crossing time (timing jitter) by an amount that is
proportional to the power of the total noise injected at the threshold-crossing
and inversely proportional to the slew rate of the output voltage [2].
2 = v2n
(dvo/dt)2, (1.1)
where 2
is the timing jitter, v2n is the power of the total noise injected at
the threshold-crossing, and dvo/dt is the slew rate of the output voltage of
the oscillator at the threshold-crossing. (iii) The latch effectively rejects the
noise presented on the power and ground rails once the latch is established.
3 Laboratory Work
3.1 Oscillator
Design a four-stage CMOS fully differential current-controlled ring oscillator,as per the schematic of Fig.1.1 where all n-well pickup contacts of pMOS tran-
sistors are connected to a clean power supply. The bond wire connecting the
VDD bonding pad and the power supply pin is modeled as an ideal inductor
with its inductanceL = 0.1 nH. The inductance of the bond wire connecting
VSSand ground is neglected so that no ground bouncing is considered. The
capacitance of the bonding pads is neglected for simplicity. The width of
M34 should be at leasttwice that ofM12 in order to be able to break the
positive feedback. Over-sizing M34 will result in a large capacitance at the
output nodes, slowing down the oscillator.
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CHAPTER 1. CURRENT-CONTROLLED RING OSCILLATORS 9
VDD1
L
CL
Switching noise injector
VDD2
L
Vin+ Vin-
Vo+Vo- 4
Cross-coupled delay cell (Stage 1)
Ictrl
M1 M2M3 M4
M5 M6
Figure 1.1: Four-stage fully differential current-controlled ring oscillator
3.2 Switching Noise Injector
A static CMOS inverter whose dimension is much larger than the dimension
of the transistors in the delay stage of the oscillator is powered by the same
power supply as that of the oscillator. Let the load of the large CMOS
inverter be a large capacitor. The input of the large CMOS inverter is an
ideal square wave generator whose period is much smaller than the oscillation
period of the oscillator. This clocked large inverter is used to simulate the
injection of switching noise to the power rail of the oscillator.
3.3 Simulation and Analysis
Construct the symbol of the delay cell of the oscillator that has (i)
two input terminals vin+ and vin, (ii) two output terminals vo+ and
vo, (iii) one VDD connection terminal, (iv) one VSSconnection termi-
nal, (v) one n-well connection terminal vnwell, and (vi) one substrate
connection terminal vsub, as per Fig.1.2.
Construct the current controlled oscillator by including (i) all delaystags, (ii) the biasing circuit, (iii) the switching noise injection circuit,
and (iv)VDD andVSS circuitry including bonding wires.
Perform time-domain analysis of the designed oscillator. The start of
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CHAPTER 1. CURRENT-CONTROLLED RING OSCILLATORS 10
Delay cell
Vin+
Vin-
Vo-
Vo+
VDD Vn-well
VSS Vsub
Figure 1.2: Symbol of the delay cell of fully differential current-controlled
ring oscillator
the oscillation of the oscillators can be activated by connecting a small
capacitor to the output node of one of the delay stages of the oscillator
with an initial voltage. Note that the value of the capacitor should be
small in order to minimize unwanted loading effect.
Plot the output voltage of each stage of the oscillator with two different
transistor widths of the latch. Measure the timing jitter. Comment on
the waveform difference.
Plot the output voltage of each stage of the oscillator with two different
control currents. Measure the rise and fall times of the output voltage
in both cases. Measure the timing jitter. Comment on your findings.
Use parametric analysisand calculator tools to obtain the oscillation
frequency-control current plot. Estimate the frequency tuning range
and frequency control sensitivity of the designed oscillator.
4 Laboratory ReportA professionally prepared laboratory report containing the followings is due
at the start of the next laboratory.
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CHAPTER 1. CURRENT-CONTROLLED RING OSCILLATORS 11
The schematic of the current-controlled oscillator (delay cell + entire
test circuit) with a boarder section showing your name and student ID.
A table tabulating the exact dimension of all transistors used in your
design.
The waveform of the voltage of the output of each stage of the current-
controlled oscillator with two different transistor widths of the latch.
Measure the peak-to-peak timing jitter at the threshold-crossing points
of the output waveform of the oscillator.
The waveforms of the voltage of the output of each stage of the current-controlled oscillator with two different control currents. Measured the
rise and fall times in these two cases. Measure the peak-to-peak timing
jitter at the threshold-crossing points of the output waveform of the
oscillator.
Oscillation frequency - control current plot. Determine the frequency
tuning range and frequency control sensitivity.
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Bibliography
[1] X. Mailand, F. Devisch, and M. Kuijk, A 900 Mb/s CMOS data re-
covery DLL using half-frequency clock, IEEE Journal of Solid-State
Circuits, vol. 37, No. 6, pp 711-715, June 2002.
[2] T. Weigandt, B. Kim, and P. Grey, Analysis of timing jitter in ring
oscillators, inProc. of IEEE International Symposium on Circuits and
Systems, pp. 27-30, London, 1994.
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Chapter 2
D-flipflop Phase/Frequency
Detectors
1 Duration : 2 weeks
2 Introduction
Phase/frequency detectors (PFDs) are one of the vital building blocks of
phase-locked loops (PLLs) and delay-locked loops (DLLs). The main func-
tionality of PFDs is to sense the phase/frequency difference between an input
digital stream and a reference clock and to output a pair of phase/frequency-
modulated pulses called UP and DOWN whose pulse width is directly pro-
portional to the phase/frequency difference. The output signals UP and
DOWN are then used to control a downstream charge pump whose output
voltage controls the oscillation frequency of a downstream voltage (current)-
controlled oscillator.
In this laboratory, you will investigate the characteristics of a widely
used phase/frequency detector called D-flipflop phase/frequency detector.
The D-flipflop phase/frequency detector employs two positive edge-triggered
resettable D-flipflops to detect the phase/frequency difference of two input
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CHAPTER 2. D-FLIPFLOP PHASE/FREQUENCY DETECTORS 14
digital signals, as shown in Fig.2.1. The output voltage waveforms with
A leading B are shown in the figure. The waveforms for B leading A arethe same as those for A leading B due to the symmetrical structure of the
phase/frequency detector.
3 Laboratory Work
3.1 D-Flipflops
There are a number of ways to construct a D-flipflop in CMOS. Conventional
implementations of D-flipflop, such as the one shown in Fig.2.2(a), suffersfrom a large number of transistors, high power consumption, and a long
propagation delay. True-single-phase-clocking (TSPC) logic circuits initially
developed in [1] offer the advantages of a low transistor count, a small chip
area, and a fast transient response. In this laboratory, TSPC logic circuits
are employed to construct the D-flipflop, as shown in Fig.2.2(b) [2, 3]. Only
6 transistors are needed for the construction of the positive-edge triggered
D-flipflop.
3.2 D-Flipflops with RESET
Modify the D-flipflop of Fig.2.2(b) by adding a RESET control mechanism
that resets Q to Logic-0 when RESET=1. Measure the propagation delay
fromD toQand record the delay.
3.3 AND2 Gate
Construct the schematic of an static AND2 gate. Construct the symbol of
the AND2 gate. Measure the average propagation delay of the AND2 gateand record the delay.
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CHAPTER 2. D-FLIPFLOP PHASE/FREQUENCY DETECTORS 15
DQ
R
DQ
R
A
B
0
Vm
A
B
Q
Vm
A
B
A
QB
A
B
QmA
QB
V /40
0(a) (b)
0
Vm
QA QB
Figure 2.1: D flip-flop phase/frequency detector.
3.4 D-flipflop Phase/Frequency Detector
Construct the schematic of the D-flipflop phase/frequency detector. Apply
two square wavesAand B of the same oscillation period and duty cycle but
difference phases to the phase/frequency detector. Let input A lead input B
with a phase difference . The following simulations are to be carried outin the laboratory work.
Plot the waveform of QA and QB when is in the neighborhood
of zero. Both QA and QB for > 0 and < 0 are considered.
Estimate the average value ofQA and QB over a period.
Plot the waveform ofQA and QB when is in the neighborhood of2
. BothQAandQB for > 2
and < 2
are considered. Estimate
the average value ofQA and QB over a period.
Plot the waveform ofQA and QB when is in the neighborhood of
. BothQA andQB for > and < are considered. Estimate
the average value ofQA and QB over a period.
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CHAPTER 2. D-FLIPFLOP PHASE/FREQUENCY DETECTORS 16
D
Q
D
CLK
Q
Q
(a) (b)
CLK
CLK
CLK
CLK
Figure 2.2: D flip-flops.
Plot the waveform ofQAand QBwhen is in the neighborhood of 32
.
Both QA and QB for > 32 and < 32 are considered. Estimatethe average value ofQA and QB over a period.
Plot the waveform ofQA and QB when approaches 2. Estimate
the average value ofQA and QB over a period.
Use the above estimated average value ofQAandQBto construct a plot
shown the relation between average output voltage and phase differ-
ence, i.e. the transfer characteristics of the D-flipflop phase/frequency
detector.
4 Laboratory Report
A professionally prepared laboratory report containing the followings is due
at the start of the next laboratory.
The schematic of the resetabble D-flipflop with a boarder section show-
ing your name and student ID.
The schematic of the AND2 gate with a boarder section showing yourname and student ID.
The schematic of the D-flipflop phase/frequency detector with a boarder
section showing your name and student ID.
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CHAPTER 2. D-FLIPFLOP PHASE/FREQUENCY DETECTORS 17
A table tabulating the exact dimension of all transistors used in your
design.
The waveform ofQA andQB when is in the neighborhood of zero.
The plot ofQA andQB for > 0 and 2
and < 2
are required.
The waveform ofQA and QB when is in the neighborhood of .
The plot ofQA andQB for > and < are required.
The waveform ofQA and QB when is in the neighborhood of 32
.
The plot ofQA andQB for > 32
and < 32
are required.
The waveform ofQA andQB when approaches 2.
The plot Average output voltage versus phase difference.
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Bibliography
[1] J. Yuan and C. Svensson, New single-clock CMOS latches and flipflops
with improved speed and power savings, IEEE J. Solid-State Circuits,
vol. 32, No.1, pp. 62-69, Jan. 1997.
[2] J. Rabaey, Digital Integrated Circuits : A Design Perspective, Upper
Saddle River, NJ : Prentice-Hall, 1996.
[3] K. Martin, Digital Integrated Circuit Design, New York : Oxford Uni-
versity Press, 2000.
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Chapter 3
Phase-Locked Loops
1 Duration: 2 weeks
2 Introduction
Phase locked loops are used extensively in data communications, computer
systems, RF communications, instrumentation, and signal processing. The
basic configuration of type II phase-locked loops is shown in Fig.3.1. The
phase/frequency detector detects the phase/frequency difference between theincoming signal Vin and the output of the local ring oscillator and converts
the phase/frequency difference into two Boolean control signals UP and DN.
The pulse width of UP and DN is proportional to the phase difference. UP
and DN are then fed to the downstream charge pump whose mainly function
is to convert UP and DN pulses into currents of constant amplitude. When
UP=1 and DN=0, JUP is conveyed to the loop filter, increasing the output
voltage of the loop filter. When UP=0 and DN=1, JDN is sinked from the
loop filter, lowering the output voltage of the loop filter. The loop filter
is a low-pass that filters out the high-frequency components of the output
current of the preceding charge pump and outputs a voltage. The output of
the loop filter is a dc voltage that controls the oscillation frequency of the
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CHAPTER 3. PHASE-LOCKED LOOPS 20
downstream voltage-controlled oscillator (VCO). The oscillation frequency
(period) of the VCO is proportional to the phase difference between Vinand Vo of the VCO. By adjusting the oscillation period of the VCO, the
phase/frequency difference can be driven to zero.
Vin
J
JC1
UP
DN
UP
DN
Vvco C2
R2
Charge pump
Loop filter
PFDVoltage-controlled oscillator
Figure 3.1: Basic configuration of type II phase-locked loops.
In this laboratory, you are required to design a phase-locked loop that
makes use of the fully differential cross-coupled 4-stage voltage-controlled
oscillator and the D-flipflop phase/frequency detector designed in previous
laboratories. In order to construct the phase-locked loop, you are also re-
quired to design and analyze two additional function blocks of phase-lockedloops, namely the charge pump and the loop filter, as shown in Fig.3.1.
3 Laboratory Work
3.1 Charge Pumps
The main functionality of a charge pump is to convert the width-modulated
pulses UP and DN from the preceding D-flipflop phase/frequency detector
into a current whose amplitude is constant and whose direction is controlledby UP and DN signals. A charge pump is essentially a digital-to-analog
converter. Fig.3.2 is the schematic of a current-steering charge pump. The
charge pump conveys a constant current JUPto or sinks a constant current
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CHAPTER 3. PHASE-LOCKED LOOPS 21
JDNfrom the output node, depending upon the control signals UP and DN
from the preceding D-flipflop phase/frequency detector. For more informa-tion on charge pumps, please read reference [1] and the main reference text
of the course.
Construct the schematic of the charge pump and its symbol. The charge
pump symbol should have the following inputs : UP, UP, DN, DN, Vout,VDD
andVSS. All n-well and substrate contacts are connected to the same power
supply and ground as those of the charge pump.
JUP
UPUP
JDN
DNDN
vo
M1 M2M3 M4
M5M6
Figure 3.2: Current-steering charge pump. The charge pump conveys JUP to
the downstream loop filter when UP=1 and DN=0. It sinksJDN from theloop filter when DN=1 and UP=0.
An implementation of the preceding charge pump is shown in Fig.3.3.
The current sources JUP and JDN are generated by the current reference
circuit consisting ofM79 and the two current mirrorsM910 andM911. Vcp
is an external voltage that controls the value ofJUP andJDN. Vcp should be
assigned as a variable so that it can be adjusted during simulation. You can
also make use of advanced biasing circuits studied in ELE704. Note that JUP
and JDNmust not be too small as they directly affect how fast the controlvoltage can be controlled by UP and DN signals. They must also not be too
large to avoid instability of the phase-locked loop.
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CHAPTER 3. PHASE-LOCKED LOOPS 22
UPUP DNDN
vo
M1 M2M3 M4
M5M6Vcp M7
M8
M9
M10 M11
Figure 3.3: Implementation of the current-steering charge pump.
3.2 Loop Filters
In order to convert the output current of the preceding charge pump into a
voltage whose value is proportional to the pulse width of the control signals
UP and DN of the charge pump, a loop filter consisting of two capacitors C1
and C2 and a resistor R2 is employed at the output of the charge pump, as
shown in Fig.3.1. Note thatC2C1. C2 and R2 form the main part of the
loop filter. Note that high-frequency sparks can pass throughR2
C2networkand create reference spursat the output of the oscillator. To minimize this
unwanted effect, a smaller capacitor C1 is used in parallel with R2 C2 to
filter out the high-frequency sparks.
Construct the schematic of the loop filter and its symbol. The value of
C1, C2, and R2 should be assigned as variables so that they can be tuned
when the phase-locked loop is constructed.
3.3 Open-Loop Test
Construct an open-loop test schematic containing (i) the D-flipflop phase/frequency
detector, (ii) the current-steering charge pump, and (iii) the loop filter de-
sign, as per Fig.3.4. Apply two 900 MHz square waves A and B of the same
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CHAPTER 3. PHASE-LOCKED LOOPS 23
oscillation period and duty cycle to the D-flipflop phase/frequency detector.
Let input Alead input B with a phase difference . Use parametricanal-ysis of Cadence to sweep and plot the waveform of the output voltage of
the loop filter. Repeat the simulation with A lagging B.
PD
J
JC1
UP
DN
UP
DNC2R2
Charge pump
Loop filter
AB Vc
Figure 3.4: Open-loop test circuit.
3.4 Closed-Loop Test
Construct a 4-stage fully differential cross-coupled voltage-controlled oscilla-
tor as per Fig.3.5. The VCO is very similar to the CCO that you designed inprevious laboratories except that the oscillation frequency is now controlled
by a voltage rather than a current. The oscillation frequency of the oscillator
should be in the neighborhood of 900 MHz. Simulate the VCO for a given
control voltage Vc and record the oscillation period (frequency). Make sure
that the oscillation frequency of the oscillator covers 900 MHz.
Construct a test schematic containing (i) the D-flipflop phase/frequency
detector, (ii) the current-steering charge pump, (iii) the loop filter design,
and the 4-stage 900 MHz fully differential cross-coupled voltage-controlled
oscillator as per Fig.3.5. Apply a 900 MHz square wave to the inputA of the
phase/frequency detector. The other input of the phase/frequency detector
B comes from the output of your VCO. Plot the waveform of A and B, as
well as the control voltage Vc of the VCO. When a lock state of the PLL
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CHAPTER 3. PHASE-LOCKED LOOPS 24
Vin+ Vin-
Vo+Vo-
Vc
Vc
Figure 3.5: Fully differential cross-coupled voltage-controlled oscillator.
is established, the phase difference between A and B should be zero and
the control voltage Vc of the VCO should settle down to a constant valueapproximately.
4 Laboratory Report
A professionally prepared laboratory report containing the followings is due
at the start of the next laboratory.
The schematic of the charge pump with a boarder section showing your
name and student ID.
The schematic of the open-loop test circuit with a boarder section show-
ing your name and student ID.
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CHAPTER 3. PHASE-LOCKED LOOPS 25
The response of the open-loop test circuit.
The schematic of the closed-loop test circuit with a boarder section
showing your name and student ID.
The response of the closed-loop test circuit at the locked state.
The waveform of the control voltage Vc of the VCO.
A table documenting the exact dimension of all transistors used in your
design.
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Bibliography
[1] M. El-Hage and F. Yuan, Architectures and design considerations of
CMOS charge pumps for phase-locked loops, in Proc. Canadian Conf.
Electrical and Computer Eng., Vol. 1, pp. 223-226, Montreal, May 2003.
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Chapter 4
Phase-Locked Loop Chip Set
1 Duration : 4 weeks
2 Introduction
In this laboratory, you are required to complete the schematic-level design of
a complete chip that contains the phase-locked loop that you designed in the
previous labs. Your design and simulation must take into account the effect
of
bond padsused for soldering bond wires,
bond wiresused to connect bond pads and traces,
tracesused to connect traces and pins and,
textfixtureused to model the packaging between traces and pins.
3 Models for Packaging
CMC provides many packaging options, depending upon the operation fre-
quencies of the design chips. In this lab, you will use 24 CFP (Ceramic
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CHAPTER 4. PHASE-LOCKED LOOP CHIP SET 28
Flat Pack), which has 24 pins, a small cavity and is suitable for high-
frequency (up to 4 GHz) designs. CMC has developed a library for both thepackage and testfixture for 24 CFP. These files are located in
Library :
package
Cellview :
24cfp_140_half_cell, 24cfp_140_test_fixture_half
Note that only a half of the package is provided. You need to make a
copy and rotate it to complete the package. These models are valid up to 4
GHz. CMC requires that all unused pins be grounded. This will increase the
level of signal isolation and improve the performance.
4 Models for Bond Pads
Bond pads are not part of the above package. You need to add bond pads
explicitly in your design to account for their capacitive effect. CMC does
not have bond pad cells developed in package library. CMC requires that
the bond pads must not be smaller than 6464. We use 6464in this
laboratory. You need to use this value to estimate the parasitic capacitance
of the bond pads. Bond pads should be modeled as a shunt capacitor between
signal path and the substrate. M6 M5 are to be connected together and
used for the bonding pads. You need to look at the electrical parameter file
of TSMC-0.18m CMOS technology to find out the capacitance from M5 tosubstrate per unit area to estimate the capacitance of the pads.
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CHAPTER 4. PHASE-LOCKED LOOP CHIP SET 29
5 Models for Bond Wires
Bond wires are also not part of the above package. You need to add bond
wires explicitly in your design in order to account for their inductive effect.
CMC has developed a bond wire cell located at
1) Library : package
2) Cellview : bondwire
The bond wires have a diameter of 31.75 m. The length of the bond
wires depends upon the pin/pad assignment and the location of pads. They
can only be determined once the complete layout is available. For your
simulation, we use the default parameters given in the library (hwl (horizontalwire length)=2000 m,d= 31.75m,r = 0.05,...).
6 Schematics
In order to take into account the effect of bond wires, bond pads, and pack-
aging, you need to add
Bond pads
Bond wire cells
24cfp_140_half_cell
24cfp_140_test_fixture_half
External test devices, such as supply voltage and loads can be connected
directly to the testfixture. The arrangement is shown in Fig.4.1.
7 Laboratory Work
7.1 Complete Test Circuit Construction
Construct the complete test circuit of the designed phase-locked loop. The
test circuit should contain the follows
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CHAPTER 4. PHASE-LOCKED LOOP CHIP SET 30
Your
design
Pad Bondwire
Parasitic cap. of pad
Cavity
Externalvoltagesource
Testfixture
Physical boundary
of CFP chip
Load
Figure 4.1: Simplified schematic of complete chip set
The phase-locked loop
The bonding pads.
The bonding wires.
The model for the package.
The model for the testfixture.
External power supply, ground, and input signals.
7.2 VDD and VSS Pads
To minimize the effect of switching noise, for each VDD and VSSconnection
to the outside, four pads/bond wires should be used. The number of pads
are as the followings :
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CHAPTER 4. PHASE-LOCKED LOOP CHIP SET 31
Table 4.1: Pad assignment of phase-locked loop chip set.
Type pf pads Number of pads
VDD pads 4
VSSpads 4
VCO output pads 8
Input signal pad 1
Charge pump control voltage Vcp pad 1
7.3 VCO Output Buffering
To bring the output voltage of the VCO to the outside of the chip, buffers
are needed in order to drive the parasitics of the package and the load. Add
eight voltage buffers to the eight outputs of the VCO (Two inverters are
connected in series with the first inverter of small dimensions. Note that the
first inverter should not be made large. Otherwise, it will load the VCO.).
7.4 PLL Test
Apply a 900 MHz 50% duty-cycle square wave to the input A of the phasedetector. The other input of the phase detector B comes from the output of
your VCO. Plot the waveform of A and B, as well as the control voltage Vcof
the VCO. When a lock state of the PLL is established, the phase difference
between A and B should be zero and the control voltage Vc of the VCO
should settle down to a constant value.
8 Layout of PLL
Once the simulation of the designed PLL is completed and design specifi-cations are met, it is the time to complete the physical design of the PLL
chipset. Since all of you already have the experience in layout in either
ELE704 or ELE734, you will find this step a rather enjoyable design expe-
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CHAPTER 4. PHASE-LOCKED LOOP CHIP SET 32
rience. Note that you should not make any change to the dimension of all
transistors used in your schematic-level design.
8.1 Floor-Planning of PLL
Before you proceed with the actual layout of the PLL chipset, the first step
that you should do is the floor planning. You MUST make a decision on
critical issues such as (i) where to route your power and ground rails. (ii)
Where to route signals, both low-frequency and high-frequency signals. (iii)
How to isolate high-frequency signals from others. (iv) How to assign I/O
pins. (v) How to ensure that n-wells are properly connected to the mostpositive voltage. (vi) Where to put guard rails and how to put the guard
rails. (vii) How to protect dc biasing circuits from noisy digital circuits, (viii)
How to minimize switching noise, and (xi) How to minimize the interaction
between analog and digital circuits of the PLL system.
8.2 Layout of PLL
Once the floor of your PLL is planned, you can proceed with the layout
of each functional block of your PLL. The following guidelines should be
followed in the layout : (i) Try to put all n-wells together. This will reduce
the chip area required for n-wells. Use as many as n+ pull-up connections
as possible for n-wells to ensure that n-well is uniformly connected to the
most positive voltage of the circuit. (ii) Multiple p+ pull-down connections
of the substrate should be used throughout your layout to ensure that the
substrate of your chip is uniformly connected to the ground. (iii) Use as
many as pins/pads as possible for VDD and VSS connections to minimize
the inductance of the bonding wires of VDD and VSS pads subsequently
the switching noise associated with these pads. (iv) High-frequency signalsshould be guarded with either ground or VDD rails to minimize their effect
on other parts of the circuit. The bottom line here is to minimize the loop
area of high-frequency signal lines so that their inductance is minimized.
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CHAPTER 4. PHASE-LOCKED LOOP CHIP SET 33
Note that the shielding rails increase the capacitance of the high-frequency
signal lines.
8.3 I/O Pin Assignment
The following guidelines should be followed in the assignment of I/O pads
and pins: (i) Use as many as pads and pins as possible for VDD and VSS
connections to minimize switching noise. (ii) Separate analog pins and digital
pins as far as possible. Often analog pins should be guarded with VSS pins
(shielding pins). (iii) Separate small-signal pins (input pins) and large-signal
pins (output pins) as far as possible to minimize cross-talks from the large-signal pins to the small-signal pins. You should assign input pins to one
side of the chip and output pins to the other side of the chip to physically
separate them. (iv) Avoid using corner pins and pads. They should be left
as dummy. (v) DC biasing pins and clock pins should be dealt with caution
as the former are high-frequency pins while the latter are analog pins.
8.4 Layout of Pads
Following the design rules of TSMC for pads. Use only M6 and M5 for all
pads to minimize the capacitance from the pads to the substrate.
8.5 Layout of Output Buffers
Output buffers are usually large in size and generate large switching noise and
substrate noise. To minimize their effect, the followings guidelines should be
followed : (i) Use a separate set of VDD and VSS pads and pins for the output
buffers to eliminate the injection of their switching noise to the system. (ii)
Use guard rings to isolate the output buffers from the rest of the system.
Guard ring VDD and VSS should be completely separated from those of the
rest of the system as they carry a high level of switching noise. (iii) Minimize
the length of the interconnects connecting the output buffers and their pads.
Techniques should be used to minimize the inductance of these interconnects.
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CHAPTER 4. PHASE-LOCKED LOOP CHIP SET 34
9 Laboratory Report
A professionally prepared laboratory report containing the followings is due
at the start of the next weeks laboratory.
The schematic of the complete test circuit with a board section showing
your name and student ID.
The response of the closed-loop test circuit at the locked state.
The waveform of the voltage of all eight outputs of the VCO.
The waveform of the control voltage Vc of the VCO.
The complete layout of the PLL chipset.
The post-layout simulation results of the waveform of the voltage of
all eight outputs of the VCO and that of the control voltage Vc of the
VCO.