622 Mbps Clock and Data Recovery IC
with Integrated Limiting Amplifier
ADN2804
Data Sheet
FEATURES
GENERAL DESCRIPTION
Exceeds SONET requirements for jitter transfer/
generation/tolerance
Quantizer sensitivity: 3.3 mV typical
Adjustable slice level: ±95 mV
Patented clock recovery architecture
Loss-of-signal (LOS) detect range: 2.6 mV to 18.4 mV
Independent slice level adjust and LOS detector
No reference clock required
Loss-of-lock indicator
I2C® interface to access optional features
Single-supply operation: 3.3 V
Low power: 423 mW typical
5 mm × 5 mm, 32-lead LFCSP, Pb free
The ADN2804 provides the receiver functions of quantization,
signal level detect, clock and data recovery, and data retiming
for 622 Mbps NRZ data. The ADN2804 automatically locks to
622 Mbps data without the need for an external reference clock
or programming. All SONET jitter requirements are met,
including jitter transfer, jitter generation, and jitter tolerance.
All specifications are quoted for −40°C to +85°C ambient
temperature, unless otherwise noted.
This device, together with a PIN diode and a TIA preamplifier,
can implement a highly integrated, low cost, low power fiber
optic receiver.
The receiver’s front-end loss-of-signal (LOS) detector circuit
indicates when the input signal level falls below a user-adjustable
threshold. The LOS detect circuit has hysteresis to prevent chatter
at the output.
APPLICATIONS
BPON ONT
SONET OC-12
WDM transponders
Regenerators/repeaters
Test equipment
Broadband cross-connects and routers
The ADN2804 is available in a compact 5 mm × 5 mm,
32-lead LFCSP.
FUNCTIONAL BLOCK DIAGRAM
REFCLKP/REFCLKN
(OPTIONAL)
SLICEP/SLICEN
2
LOL
CF1
CF2
FREQUENCY
DETECT
LOOP
FILTER
PHASE
DETECT
LOOP
FILTER
VCC
VEE
PIN
NIN
QUANTIZER
PHASE
SHIFTER
VCO
VREF
DATA
RE-TIMING
2
2
THRADJ
LOS
DATAOUTP/
DATAOUTN
CLKOUTP/
CLKOUTN
ADN2804
05801-001
LOS
DETECT
Figure 1.
Rev. D
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ADN2804
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Jitter Specifications ......................................................................... 13
Applications ....................................................................................... 1
Theory of Operation ...................................................................... 14
General Description ......................................................................... 1
Functional Description .................................................................. 16
Functional Block Diagram .............................................................. 1
Frequency Acquisition ............................................................... 16
Revision History ............................................................................... 2
Limiting Amplifier ..................................................................... 16
Specifications..................................................................................... 3
Slice Adjust .................................................................................. 16
Jitter Specifications ....................................................................... 4
Loss-of-Signal (LOS) Detector ................................................. 16
Output and Timing Specifications ............................................. 5
Lock Detector Operation .......................................................... 17
Absolute Maximum Ratings ............................................................ 6
SQUELCH Modes ...................................................................... 17
Thermal Characteristics .............................................................. 6
I2C Interface ................................................................................ 17
ESD Caution .................................................................................. 6
Reference Clock (Optional) ...................................................... 19
Timing Characteristics ..................................................................... 7
Applications Information .............................................................. 21
Pin Configuration and Function Descriptions ............................. 8
PCB Design Guidelines ............................................................. 21
Typical Performance Characteristics ............................................. 9
DC-Coupled Application .......................................................... 23
I2C Interface Timing and Internal Register Description ........... 10
Outline Dimensions ....................................................................... 24
Terminology .................................................................................... 12
Ordering Guide .......................................................................... 24
REVISION HISTORY
4/14—Rev. C to Rev. D
5/10—Rev. A to Rev. B
Updated Outline Dimensions ....................................................... 24
Changes to Ordering Guide .......................................................... 24
Changes to Figure 5 and Table 5......................................................8
Changes to Figure 24...................................................................... 21
1/12—Rev. B to Rev. C
2/09—Rev. 0 to Rev. A
Changed Pin 1 from VCC to TEST1 and Changed Pin 32 from
VCC to TEST2 ............................................................... Throughout
Changes to General Description .................................................... 1
Changes to Quantizer—AC Characteristics, Output Clock
Range Parameter, Table 1................................................................. 3
Changes to Table 6 and Table 10................................................... 11
Updated Outline Dimensions ....................................................... 24
Updated Outline Dimensions ....................................................... 24
Changes to Ordering Guide .......................................................... 24
2/06—Revision 0: Initial Version
Rev. D | Page 2 of 24
Data Sheet
ADN2804
SPECIFICATIONS
TA = TMIN to TMAX, VCC = VMIN to VMAX, VEE = 0 V, CF = 0.47 µF, SLICEP = SLICEN = VEE, input data pattern: PRBS 223 − 1,
unless otherwise noted.
Table 1.
Parameter
QUANTIZER—DC CHARACTERISTICS
Input Voltage Range
Peak-to-Peak Differential Input
Input Common-Mode Level
Differential Input Sensitivity
Input Offset
Input RMS Noise
QUANTIZER—AC CHARACTERISTICS
Data Rate
Output Clock Range
S11
Input Resistance
Input Capacitance
QUANTIZER—SLICE ADJUSTMENT
Gain
Differential Control Voltage Input
Control Voltage Range
Slice Threshold Offset
LOSS-OF-SIGNAL (LOS) DETECT
Loss-of-Signal Detect Range (see Figure 6)
Hysteresis (Electrical)
LOS Assert Time
LOS Deassert Time
LOSS-OF-LOCK (LOL) DETECT
VCO Frequency Error for LOL Assert
VCO Frequency Error for LOL Deassert
LOL Response Time
ACQUISITION TIME
Lock to Data Mode
Optional Lock to REFCLK Mode
DATA RATE READBACK ACCURACY
Fine Readback
POWER SUPPLY VOLTAGE
POWER SUPPLY CURRENT
OPERATING TEMPERATURE RANGE
1
2
Conditions
Min
@ PIN or NIN, dc-coupled
PIN − NIN
DC-coupled (see Figure 27, Figure 28, and Figure 29)
223 − 1 PRBS, ac-coupled,1 BER = 1 × 10–10
1.8
2.3
6
BER = 1 × 10–10
2.5
3.3
500
290
Max
Unit
2.8
2.0
2.8
V
V
V
mV p-p
µV
µV rms
622
622
−15
100
0.65
Locked to 622 Mbps input data
@ 622 MHz
Differential
SLICEP − SLICEN = ±0.5 V
SLICEP − SLICEN
DC level @ SLICEP or SLICEN
Typ
0.10
−0.95
VEE
0.11
Mbps
MHz
dB
Ω
pF
0.13
+0.95
0.95
V/V
V
V
mV
1
RTHRESH = 0 Ω
RTHRESH = 100 kΩ
OC-12
RTHRESH = 0 Ω
RTHRESH = 100 kΩ
DC-coupled2
DC-coupled2
14.9
2.6
16.7
3.5
18.4
4.4
mV
mV
6.2
4.1
6.9
6.1
500
400
7.7
8.1
dB
dB
ns
ns
With respect to nominal
With respect to nominal
OC-12
1000
250
200
ppm
ppm
µs
OC-12
2.0
20.0
ms
ms
In addition to REFCLK accuracy
OC-12
3.0
Locked to 622.08 Mbps
–40
100
3.3
128
3.6
+85
ppm
V
mA
°C
PIN and NIN should be differentially driven and ac-coupled for optimum sensitivity.
When ac-coupled, the LOS assert and deassert times are dominated by the RC time constant of the ac coupling capacitor and the 50 Ω input termination of the
ADN2804 input stage.
Rev. D | Page 3 of 24
ADN2804
Data Sheet
JITTER SPECIFICATIONS
TA = TMIN to TMAX, VCC = VMIN to VMAX, VEE = 0 V, CF = 0.47 µF, SLICEP = SLICEN = VEE, input data pattern: PRBS 223 − 1,
unless otherwise noted.
Table 2.
Parameter
PHASE-LOCKED LOOP CHARACTERISTICS
Jitter Transfer Bandwidth
Jitter Peaking
Jitter Generation
Jitter Tolerance
1
Conditions
Min
OC-12
OC-12
OC-12, 12 kHz to 5 MHz
OC-12, 223 − 1 PRBS
30 Hz1
300 Hz1
25 kHz
250 kHz1
100
44
2.5
1.0
Jitter tolerance of the ADN2804 at these jitter frequencies is better than what the test equipment is able to measure.
Rev. D | Page 4 of 24
Typ
Max
Unit
75
0
0.001
0.011
130
0.03
0.003
0.026
kHz
dB
UI rms
UI p-p
UI p-p
UI p-p
UI p-p
UI p-p
Data Sheet
ADN2804
OUTPUT AND TIMING SPECIFICATIONS
Table 3.
Parameter
LVDS OUTPUT CHARACTERISTICS
(CLKOUTP/CLKOUTN, DATAOUTP/DATAOUTN)
Output Voltage High
Output Voltage Low
Differential Output Swing
Output Offset Voltage
Output Impedance
LVDS Outputs’ Timing
Rise Time
Fall Time
Setup Time
Hold Time
I2C INTERFACE DC CHARACTERISTICS
Input High Voltage
Input Low Voltage
Input Current
Output Low Voltage
I2C INTERFACE TIMING
SCK Clock Frequency
SCK Pulse Width High
SCK Pulse Width Low
Start Condition Hold Time
Start Condition Setup Time
Data Setup Time
Data Hold Time
SCK/SDA Rise/Fall Time
Stop Condition Setup Time
Bus Free Time Between a Stop and a Start
REFCLK CHARACTERISTICS
Input Voltage Range
Minimum Differential Input Drive
Reference Frequency
Required Accuracy
LVTTL DC INPUT CHARACTERISTICS
Input High Voltage
Input Low Voltage
Input High Current
Input Low Current
LVTTL DC OUTPUT CHARACTERISTICS
Output High Voltage
Output Low Voltage
1
Conditions
Min
VOH (see Figure 3)
VOL (see Figure 3)
VOD (see Figure 3)
VOS (see Figure 3)
Differential
925
250
1125
20% to 80%
80% to 20%
TS (see Figure 2), OC-12
TH (see Figure 2), OC-12
LVCMOS
VIH
VIL
VIN = 0.1 VCC or VIN = 0.9 VCC
VOL, IOL = 3.0 mA
See Figure 11
760
760
Typ
Max
Unit
1475
mV
mV
mV
mV
Ω
320
1200
100
400
1275
115
115
800
800
220
220
840
840
ps
ps
ps
ps
0.3 VCC
+10.0
0.4
V
V
µA
V
0.7 VCC
−10.0
400
tHIGH
tLOW
tHD;STA
tSU;STA
tSU;DAT
tHD;DAT
TR/TF
tSU;STO
tBUF
Optional lock to REFCLK mode
@ REFCLKP or REFCLKN
VIL
VIH
600
1300
600
600
100
300
20 + 0.1 Cb1
600
1300
300
0
VCC
100
10
160
100
VIH
VIL
IIH, VIN = 2.4 V
IIL, VIN = 0.4 V
VOH, IOH = −2.0 mA
VOL, IOL = +2.0 mA
Cb = total capacitance of one bus line in picofarads. If used with Hs-mode devices, faster fall times are allowed.
Rev. D | Page 5 of 24
2.0
0.8
5
−5
2.4
0.4
kHz
ns
ns
ns
ns
ns
ns
ns
ns
ns
V
V
mV p-p
MHz
ppm
V
V
µA
µA
V
V
ADN2804
Data Sheet
ABSOLUTE MAXIMUM RATINGS
TA = TMIN to TMAX, VCC = VMIN to VMAX, VEE = 0 V, CF =
0.47 µF, SLICEP = SLICEN = VEE, unless otherwise noted.
Table 4.
Parameter
Supply Voltage (VCC)
Minimum Input Voltage (All Inputs)
Maximum Input Voltage (All Inputs)
Maximum Junction Temperature
Storage Temperature Range
Rating
4.2 V
VEE − 0.4 V
VCC + 0.4 V
125°C
−65°C to +150°C
Stress above those listed under Absolute Maximum Ratings may
cause permanent damage to the device. This is a stress rating
only; functional operation of the device at these or any other
conditions above those indicated in the operational sections of
this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
THERMAL CHARACTERISTICS
Thermal Resistance
32-lead LFCSP, 4-layer board with exposed paddle soldered to
VEE, θJA = 28°C/W.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. D | Page 6 of 24
Data Sheet
ADN2804
TIMING CHARACTERISTICS
CLKOUTP
TH
05801-002
TS
DATAOUTP/
DATAOUTN
Figure 2. Output Timing
DIFFERENTIAL CLKOUTP/N, DATAOUTP/N
VOH
VOS
05801-032
|VOD|
VOL
Figure 3. Differential Output Specifications
5mA
RLOAD
100Ω
100Ω
VDIFF
SIMPLIFIED LVDS
OUTPUT STAGE
Figure 4. Differential Output Stage
Rev. D | Page 7 of 24
05801-033
5mA
ADN2804
Data Sheet
32 TEST2
31 VCC
30 VEE
29 DATAOUTP
28 DATAOUTN
27 SQUELCH
26 CLKOUTP
25 CLKOUTN
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
ADN2804*
TOP VIEW
(Not to Scale)
24 VCC
23 VEE
22 LOS
21 SDA
20 SCK
19 SADDR5
18 VCC
17 VEE
* THERE IS AN EXPOSED PAD ON THE BOTTOM OF
THE PACKAGE THAT MUST BE CONNECTED TO GND.
05801-004
PIN 1
INDIC ATOR
THRADJ 9
REFCLKP 10
REFCLKN 11
VCC 12
VEE 13
CF2 14
CF1 15
LOL 16
TEST1 1
VCC 2
VREF 3
NIN 4
PIN 5
SLICEP 6
SLICEN 7
VEE 8
Figure 5. Pin Configuration
Table 5. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Exposed Pad
1
Mnemonic
TEST1
VCC
VREF
NIN
PIN
SLICEP
SLICEN
VEE
THRADJ
REFCLKP
REFCLKN
VCC
VEE
CF2
CF1
LOL
VEE
VCC
SADDR5
SCK
SDA
LOS
VEE
VCC
CLKOUTN
CLKOUTP
SQUELCH
DATAOUTN
DATAOUTP
VEE
VCC
TEST2
Pad
Type1
P
AO
AI
AI
AI
AI
P
AI
DI
DI
P
P
AO
AO
DO
P
P
DI
DI
DI
DO
P
P
DO
DO
DI
DO
DO
P
P
P
Description
Connect to VCC.
Power for Limiting Amplifier, LOS.
Internal VREF Voltage. Decouple to GND with a 0.1 µF capacitor.
Differential Data Input. CML.
Differential Data Input. CML.
Differential Slice Level Adjust Input.
Differential Slice Level Adjust Input.
GND for Limiting Amplifier, LOS.
LOS Threshold Setting Resistor.
Differential REFCLK Input. 10 MHz to 160 MHz.
Differential REFCLK Input. 10 MHz to 160 MHz.
VCO Power.
VCO GND.
Frequency Loop Capacitor.
Frequency Loop Capacitor.
Loss-of-Lock Indicator. LVTTL active high.
FLL Detector GND.
FLL Detector Power.
Slave Address Bit 5.
I2C Clock Input.
I2C Data Input.
Loss-of-Signal Detect Output. Active high. LVTTL.
Output Buffer, I2C GND.
Output Buffer, I2C Power.
Differential Recovered Clock Output. LVDS.
Differential Recovered Clock Output. LVDS.
Disable Clock and Data Outputs. Active high. LVTTL.
Differential Recovered Data Output. LVDS.
Differential Recovered Data Output. LVDS.
Phase Detector, Phase Shifter GND.
Phase Detector, Phase Shifter Power.
Connect to VCC.
Connect to GND.
Type: P = power, AI = analog input, AO = analog output, DI = digital input, DO = digital output.
Rev. D | Page 8 of 24
Data Sheet
ADN2804
TYPICAL PERFORMANCE CHARACTERISTICS
16
12
10
8
6
4
2
1
10
100
1k
10k
Figure 6. LOS Comparator Trip Point Programming
Rev. D | Page 9 of 24
100k
05801-005
TRIP POINT (mV p-p)
14
ADN2804
Data Sheet
I2C INTERFACE TIMING AND INTERNAL REGISTER DESCRIPTION
1
A5
MSB = 1
SET BY
PIN 19
0
0
0
0
0
X
0 = WR
1 = RD
05801-007
R/W
CTRL.
SLAVE ADDRESS [6...0]
S
SLAVE ADDR, LSB = 0 (WR) A(S) SUB ADDR A(S) DATA A(S)
DATA A(S)
P
05801-008
Figure 7. Slave Address Configuration
Figure 8. I2C Write Data Transfer
SLAVE ADDR, LSB = 0 (WR) A(S) SUB ADDR
A(S) S SLAVE ADDR, LSB = 1 (RD) A(S) DATA
A(M)
DATA A(M) P
P = STOP BIT
A(M) = LACK OF ACKNOWLEDGE BY MASTER
A(M) = ACKNOWLEDGE BY MASTER
05801-009
S
S = START BIT
A(S) = ACKNOWLEDGE BY SLAVE
Figure 9. I2C Read Data Transfer
SDA
SLAVE ADDRESS
A6
SUB ADDRESS
A5
A7
STOP BIT
DATA
A0
D7
D0
SCK
S
WR
ACK
ACK
SLADDR[4...0]
ACK
SUB ADDR[6...1]
DATA[6...1]
Figure 10. I2C Data Transfer Timing
tF
tSU;DAT
tHD;STA
tBUF
SDA
tR
tR
tSU;STO
tF
tLOW
tHIGH
tHD;STA
S
tSU;STA
S
tHD;DAT
Figure 11. I2C Port Timing Diagram
Rev. D | Page 10 of 24
P
S
05801-011
SCK
P
05801-010
START BIT
Data Sheet
ADN2804
Table 6. Internal Register Map1
Reg
Name
FREQ0
FREQ1
FREQ2
MISC
R/W
R
R
R
R
Addr
0x0
0x1
0x2
0x4
D7
MSB
MSB
0
x
CTRLA
CTRLB
W
W
0x8
0x9
CTRLC
W
0x11
FREF range
Config Reset
LOL
MISC[4]
0
0
1
D6
D5
D4
D3
MSB
x
LOS status
Static
LOL
LOL
status
System
reset
0
D2
D1
Data rate
measurement
complete
Data rate/DIV_FREF ratio
0
Reset
0
MISC[2]
0
0
Config LOS
x
D0
LSB
LSB
LSB
x
Measure data rate
0
Lock to reference
0
SQUELCH mode
0
All writeable registers default to 0x00.
Table 7. Miscellaneous Register, MISC
D7
x
D6
x
LOS Status
D5
0 = No loss of signal
1 = Loss of signal
Static LOL
D4
0 = Waiting for next LOL
1 = Static LOL until reset
LOL Status
D3
0 = Locked
1 = Acquiring
Data Rate Measurement Complete
D2
0 = Measuring data rate
1 = Measurement complete
D1
x
D0
x
Table 8. Control Register, CTRLA1
FREF Range
D7
D6
0
0
0
1
1
0
1
1
1
Data Rate/Div_FREF Ratio
D5
D4
D3
D2
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
19.44 MHz
38.88 MHz
77.76 MHz
155.52 MHz
32
32
32
32
Measure Data Rate
D1
Set to 1 to measure data rate
Lock to Reference
D0
0 = Lock to input data
1 = Lock to reference clock
Where DIV_FREF is the divided down reference referred to the 10 MHz to 20 MHz band (see the Reference Clock (Optional) section).
Table 9. Control Register, CTRLB
Config LOL
D7
0 = LOL pin normal operation
1 = LOL pin is static LOL
Reset MISC[4]
D6
Write a 1 followed
by 0 to reset MISC[4]
System Reset
D5
Write a 1 followed by
0 to reset ADN2804
D4
Set to 0
Reset MISC[2]
D3
Write a 1 followed
by 0 to reset MISC[2]
D2
Set to 0
D1
Set to 0
D0
Set to 0
Table 10. Control Register, CTRLC
D7
Set to 0
D6
Set to 0
D5
Set to 0
D4
Set to 0
D3
Set to 0
Config LOS
D2
0 = Active high LOS
1 = Active low LOS
Rev. D | Page 11 of 24
SQUELCH Mode
D1
0 = Squelch data outputs and
clock outputs
1 = Squelch data outputs or
clock outputs
D0
0 (Default output swing)
ADN2804
Data Sheet
TERMINOLOGY
OUTPUT
NOISE
1
10mV p-p
VREF
SCOPE
PROBE
ADN2804
PIN
+
QUANTIZER
–
50Ω
Figure 13. Single-Ended Sensitivity Measurement
When the ADN2804 is driven differentially (see Figure 14),
sensitivity seems to improve if observing the quantizer input
with an oscilloscope probe. This is an illusion caused by the use
of a single-ended probe. A 5 mV p-p signal appears to drive the
ADN2804 quantizer; however, the single-ended probe measures
only half the signal. The true quantizer input signal is twice this
value, because the other quantizer input is a complementary
signal to the signal being observed.
5mV p-p
0
INPUT (V p-p)
SCOPE
PROBE
PIN
+
OVERDRIVE
QUANTIZER
05801-012
SENSITIVITY
(2 × OVERDRIVE)
2.5V
3kΩ
VREF
OFFSET
50Ω
VREF
05801-013
Input Sensitivity and Input Overdrive
Sensitivity and overdrive specifications for the quantizer involve
offset voltage, gain, and noise. The relationship between the
logic output of the quantizer and the analog voltage input is
shown in Figure 12. For sufficiently large positive input voltage,
the output is always Logic 1; similarly, for negative inputs, the
output is always Logic 0. However, the transitions between
output Logic Level 1 and output Logic Level 0 are not at
precisely defined input voltage levels, but occur over a range of
input voltages. Within this range of input voltages, the output
may be either 1 or 0, or it may even fail to attain a valid logic
state. The width of this zone is determined by the input voltage
noise of the quantizer. The center of the zone is the quantizer
input offset voltage. Input overdrive is the magnitude of signal
required to guarantee the correct logic level with 1 × 10−10
confidence level.
NIN
–
Figure 12. Input Sensitivity and Input Overdrive
50Ω
VREF
50Ω
VREF
5mV p-p
3kΩ
2.5V
05801-014
Single-Ended vs. Differential
AC coupling is typically used to drive the inputs to the
quantizer. The inputs are internally dc biased to a commonmode potential of ~2.5 V. Driving the ADN2804 in a singleended fashion and observing the quantizer input with an
oscilloscope probe at the point indicated in Figure 13 shows a
binary signal with an average value equal to the common-mode
potential and instantaneous values both above and below the
average value. It is convenient to measure the peak-to-peak
amplitude of this signal and call the minimum required value
the quantizer sensitivity. Referring to Figure 13, the sensitivity is
twice the overdrive because both positive and negative offsets
need to be accommodated. The ADN2804 quantizer typically
has 3.3 mV p-p sensitivity.
Figure 14. Differential Sensitivity Measurement
LOS Response Time
LOS response time is the delay between removal of the input
signal and indication of loss of signal (LOS) at the LOS output,
Pin 22. When the inputs are dc-coupled, the LOS assert time of
the AD2804 is 500 ns typical and the deassert time is 400 ns
typical. In practice, the time constant produced by the ac
coupling at the quantizer input and the 50 Ω on-chip input
termination determines the LOS response time.
Rev. D | Page 12 of 24
Data Sheet
ADN2804
JITTER SPECIFICATIONS
The ADN2804 CDR is designed to achieve the best biterror-rate (BER) performance and to exceed the jitter
transfer, generation, and tolerance specifications proposed
for SONET/SDH equipment defined in the Telcordia
Technologies specification.
Jitter Generation
The jitter generation specification limits the amount of jitter
that can be generated by the device with no jitter and wander
applied at the input. For SONET devices, the jitter generated
must be less than 0.01 UI rms and less than 0.1 UI p-p.
Jitter Transfer
The jitter transfer function is the ratio of the jitter on the output
signal to the jitter applied on the input signal vs. the frequency.
This parameter measures the amount of jitter on an input signal
that can be transferred to the output signal (see Figure 15). This
amount is limited.
05801-015
fC
JITTER FREQUENCY (kHz)
Figure 15. Jitter Transfer Curve
Jitter Tolerance
The jitter tolerance is defined as the peak-to-peak amplitude of
the sinusoidal jitter applied on the input signal, which causes a
1 dB power penalty. This is a stress test intended to ensure that
no additional penalty is incurred under the operating
conditions (see Figure 16).
15.00
SLOPE = –20dB/DECADE
1.50
0.15
f0
f1
f2
f3
JITTER FREQUENCY (kHz)
Figure 16. SONET Jitter Tolerance Mask
Rev. D | Page 13 of 24
f4
05801-016
The following sections briefly summarize the specifications of
jitter generation, transfer, and tolerance in accordance with the
Telcordia document (GR-253-CORE, Issue 3, September 2000)
for the optical interface at the equipment level and the
ADN2804 performance with respect to those specifications.
SLOPE = –20dB/DECADE
ACCEPTABLE
RANGE
INPUT JITTER AMPLITUDE (UI p-p)
Jitter is the dynamic displacement of digital signal edges from
their long-term average positions, measured in unit intervals
(UI), where 1 UI = 1 bit period. Jitter on the input data can
cause dynamic phase errors on the recovered clock sampling
edge. Jitter on the recovered clock causes jitter on the
retimed data.
JITTER GAIN (dB)
0.1
ADN2804
Data Sheet
THEORY OF OPERATION
Another view of the circuit is that the phase shifter implements
the zero required for frequency compensation of a second-order
phase-locked loop, and this zero is placed in the feedback path;
therefore, it does not appear in the closed-loop transfer
function. Jitter peaking in a conventional second-order phaselocked loop is caused by the presence of this zero in the closedloop transfer function. Because this circuit has no zero in the
closed-loop transfer, jitter peaking is minimized.
The delay and phase loops together simultaneously provide
wideband jitter accommodation and narrow-band jitter
filtering. The linearized block diagram in Figure 17 shows that
the jitter transfer function, Z(s)/X(s), provides excellent secondorder low-pass filtering. Note that the jitter transfer has no zero,
unlike an ordinary second-order phase-locked loop. This means
that the main PLL loop has virtually no jitter peaking (see
Figure 18), making this circuit ideal for signal regenerator
applications, where jitter peaking in a cascade of regenerators
can contribute to hazardous jitter accumulation.
The error transfer, e(s)/X(s), has the same high-pass form as an
ordinary phase-locked loop. This transfer function can be
optimized to accommodate a significant amount of wideband
jitter, because the jitter transfer function, Z(s)/X(s), provides the
narrow-band jitter filtering.
INPUT
DATA
X(s)
e(s)
o/s
d/sc
1/n
Z(s)
RECOVERED
CLOCK
d = PHASE DETECTOR GAIN
o = VCO GAIN
c = LOOP INTEGRATOR
psh = PHASE SHIFTER GAIN
n = DIVIDE RATIO
JITTER TRANSFER FUNCTION
Z(s)
1
=
n psh
cn
X(s)
+1
+s
s2
o
do
TRACKING ERROR TRANSFER FUNCTION
05801-017
e(s)
s2
=
d psh do
X(s)
+
s2 + s
c
cn
Figure 17. PLL/DLL Architecture
JITTER PEAKING
IN ORDINARY PLL
ADN2804
Z(s)
X(s)
o
n psh
d psh
c
FREQUENCY (kHz)
05801-018
The delay and phase loops together track the phase of the input
data signal. For example, when the clock lags the input data, the
phase detector drives the VCO to a higher frequency and
increases the delay through the phase shifter; both of these
actions serve to reduce the phase error between the clock and
the data. The faster clock picks up phase, whereas the delayed
data loses phase. Because the loop filter is an integrator, the
static phase error is driven to 0°.
psh
JITTER GAIN (dB)
The ADN2804 is a delay- and phase-locked loop circuit for
clock recovery and data retiming from an NRZ encoded data
stream. The phase of the input data signal is tracked by two
separate feedback loops, which share a common control voltage.
A high speed delay-locked loop path uses a voltage controlled
phase shifter to track the high frequency components of input
jitter. A separate phase control loop, composed of the VCO,
tracks the low frequency components of input jitter. The initial
frequency of the VCO is set by yet a third loop that compares
the VCO frequency with the input data frequency and sets the
coarse tuning voltage. The jitter tracking phase-locked loop
controls the VCO by the fine-tuning control.
Figure 18. Jitter Response vs. Conventional PLL
The delay and phase loops contribute to overall jitter accommodation. At low frequencies of input jitter on the data signal,
the integrator in the loop filter provides high gain to track large
jitter amplitudes with small phase error. In this case, the VCO is
frequency modulated, and jitter is tracked as in an ordinary
phase-locked loop. The amount of low frequency jitter that can
be tracked is a function of the VCO tuning range. A wider
tuning range gives larger accommodation of low frequency
jitter. The internal loop control voltage remains small for small
phase errors; therefore, the phase shifter remains close to the
center of its range and thus contributes little to the low
frequency jitter accommodation.
Rev. D | Page 14 of 24
Data Sheet
ADN2804
At medium jitter frequencies, the gain and tuning range of the
VCO are not large enough to track input jitter. In this case, the
VCO control voltage becomes large and saturates, and the VCO
frequency dwells at one extreme of its tuning range. The size of
the VCO tuning range, therefore, has only a small effect on the
jitter accommodation. The delay-locked loop control voltage is
now larger; therefore, the phase shifter takes on the burden of
tracking the input jitter. The phase shifter range, in UI, can be
seen as a broad plateau on the jitter tolerance curve. The phase
shifter has a minimum range of 2 UI at all data rates.
The gain of the loop integrator is small for high jitter
frequencies; therefore, larger phase differences are needed to
increase the loop control voltage enough to tune the range of
the phase shifter. However, large phase errors at high jitter
frequencies cannot be tolerated. In this region, the gain of the
integrator determines the jitter accommodation. Because the
gain of the loop integrator declines linearly with frequency,
jitter accommodation is lower with higher jitter frequency. At
the highest frequencies, the loop gain is very small, and little
tuning of the phase shifter can be expected. In this case, jitter
accommodation is determined by the eye opening of the input
data, the static phase error, and the residual loop jitter generation.
The jitter accommodation is roughly 0.5 UI in this region. The
corner frequency between the declining slope and the flat region
is the closed-loop bandwidth of the delay-locked loop, which is
roughly 1.0 MHz at 622 Mbps.
Rev. D | Page 15 of 24
ADN2804
Data Sheet
FUNCTIONAL DESCRIPTION
FREQUENCY ACQUISITION
LOSS-OF-SIGNAL (LOS) DETECTOR
The ADN2804 acquires frequency from the data. The lock
detector circuit compares the frequency of the VCO and the
frequency of the incoming data. When these frequencies differ
by more than 1000 ppm, LOL is asserted. This initiates a frequency
acquisition cycle. When the VCO frequency is within 250 ppm
of the data frequency, LOL is deasserted.
The receiver front-end LOS detector circuit detects when the
input signal level falls below a user-adjustable threshold. The
threshold is set with a single external resistor from Pin 9,
THRADJ, to VEE. The LOS comparator trip point vs. the
resistor value is shown in Figure 6. If the input level to the
ADN2804 drops below the programmed LOS threshold, the
output of the LOS detector, LOS (Pin 22), is asserted to Logic 1.
The LOS detector’s response time is ~500 ns by design, but is
dominated by the RC time constant in ac-coupled applications.
The LOS pin defaults to active high. However, setting Bit
CTRLC[2] to 1, configures the LOS pin as active low.
Once LOL is deasserted, the frequency-locked loop is turned
off. The PLL/DLL pulls the VCO frequency in the rest of the
way until the VCO frequency equals the data frequency.
The frequency loop requires a single external capacitor between
CF1 and CF2, Pin 14 and Pin 15. A 0.47 μF ± 20%, X7R ceramic
chip capacitor with 300MΩ INSULATION RESISTANCE
Figure 24. Typical ADN2804 Applications Circuit
Rev. D | Page 21 of 24
05801-031
0.1µF
24
EXPOSED PAD 23
TIED OFF TO 22
VEE PLANE 21
20
WITH VIAS
19
18
17
9
10
11
12
13
14
15
16
1nF
1
2
3
4
5
6
7
8
THRADJ
REFCLKP
REFCLKN
NC
VCC
VEE
CF2
CF1
LOL
0.1µF
TEST1
VCC
VREF
NIN
PIN
SLICEP
SLICEN
VEE
VCC
ADN2804
Data Sheet
Transmission Lines
Choosing AC Coupling Capacitors
Minimizing reflections in the ADN2804 requires use of 50 Ω
transmission lines for all pins with high frequency input and
output signals, including PIN, NIN, CLKOUTP, CLKOUTN,
DATAOUTP, and DATAOUTN (also REFCLKP and REFCLKN,
if a high frequency reference clock is used, such as 155 MHz). It
is also necessary for the PIN/NIN input traces to be matched in
length and for the CLKOUTP/CLKOUTN and
DATAOUTP/DATAOUTN output traces to be matched in
length to avoid skew between the differential traces.
AC coupling capacitors at the input (PIN, NIN) and output
(DATAOUTP, DATAOUTN) of the ADN2804 can be optimized
for the application. When choosing the capacitors, the time
constant formed with the two 50 Ω resistors in the signal path
must be considered. When a large number of consecutive
identical digits (CIDs) are applied, the capacitor voltage can
droop due to baseline wander (see Figure 26), causing patterndependent jitter (PDJ).
The high speed inputs, PIN and NIN, are internally terminated
with 50 Ω to an internal reference voltage (see Figure 25).
A 0.1 μF is recommended between VREF, Pin 3, and GND to
provide an ac ground for the inputs.
The user must determine how much droop is tolerable and
choose an ac coupling capacitor based on that amount of droop.
The amount of PDJ can then be approximated based on the
capacitor selection. The actual capacitor value selection can
require some trade-offs between droop and PDJ.
As with any high speed, mixed-signal design, take care to keep
all high speed digital traces away from sensitive analog nodes.
For example, assuming that 2% droop can be tolerated, the
maximum differential droop is 4%. Normalizing to V p-p:
Droop = ΔV = 0.04 V = 0.5 V p-p (1 − e−t/τ); therefore, τ = 12t
VCC
ADN2804
CIN
PIN
50Ω
CIN
NIN
TIA
0.1µF
VREF
3Ω
where:
τ is the RC time constant (C is the ac coupling capacitor, R =
100 Ω seen by C).
t is the total discharge time, which is equal to nT, where n is the
number of CIDs, and T is the bit period.
2.5V
The capacitor value can then be calculated by combining the
equations for τ and t:
05801-026
50Ω
Figure 25. ADN2804 AC-Coupled Input Configuration
C = 12 nT/R
Soldering Guidelines for Lead Frame Chip Scale Package
The lands on the 32-lead LFCSP are rectangular. The printed
circuit board (PCB) pad for these should be 0.1 mm longer than
the package land length and 0.05 mm wider than the package
land width. The land should be centered on the pad. This
ensures that the solder joint size is maximized. The bottom of
the chip scale package has a central exposed pad. The pad on
the PCB should be at least as large as this exposed pad. The user
must connect the exposed pad to VEE using plugged vias so
that solder does not leak through the vias during reflow. This
ensures a solid connection from the exposed pad to VEE.
Once the capacitor value is selected, the PDJ can be
approximated as
PDJpspp = 0.5 tr(1 − e(−nT/RC))/0.6
where:
PDJpspp is the amount of pattern-dependent jitter allowed
(
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