a
Fiber Optic Receiver with Quantizer and
Clock Recovery and Data Retiming
AD807
reliance on external components such as a crystal or a SAW
filter, to aid frequency acquisition.
FEATURES
Meets CCITT G.958 Requirements
for STM-1 Regenerator—Type A
Meets Bellcore TR-NWT-000253 Requirements for OC-3
Output Jitter: 2.0 Degrees RMS
155 Mbps Clock Recovery and Data Retiming
Accepts NRZ Data, No Preamble Required
Phase-Locked Loop Type Clock Recovery—
No Crystal Required
Quantizer Sensitivity: 2 mV
Level Detect Range: 2.0 mV to 30 mV
Single Supply Operation: +5 V or –5.2 V
Low Power: 170 mW
10 KH ECL/PECL Compatible Output
Package: 16-Lead Narrow 150 mil SOIC
The AD807 acquires frequency and phase lock on input data
using two control loops that work without requiring external
control. The frequency acquisition control loop initially acquires
the frequency of the input data, acquiring frequency lock on
random or scrambled data without the need for a preamble. At
frequency lock, the frequency error is zero and the frequency
detector has no further effect. The phase acquisition control
loop then works to ensure that the output phase tracks the input
phase. A patented phase detector has virtually eliminated pattern
jitter throughout the AD807.
The device VCO uses a ring oscillator architecture and patented
low noise design techniques. Jitter is 2.0 degrees rms. This low
jitter results from using a fully differential signal architecture,
Power Supply Rejection Ratio circuitry and a dielectrically
isolated process that provides immunity from extraneous signals
on the IC. The device can withstand hundreds of millivolts of
power supply noise without an effect on jitter performance.
PRODUCT DESCRIPTION
The AD807 provides the receiver functions of data quantization,
signal level detect, clock recovery and data retiming for 155 Mbps
NRZ data. The device, together with a PIN diode/preamplifier
combination, can be used for a highly integrated, low cost, low
power SONET OC-3 or SDH STM-1 fiber optic receiver.
The user sets the jitter peaking and acquisition time of the PLL
by choosing a damping factor capacitor whose value determines
loop damping. CCITT G.958 Type A jitter transfer requirements can easily be met with a damping factor of 5 or greater.
The receiver front end signal level detect circuit indicates when
the input signal level has fallen below a user adjustable threshold. The threshold is set with a single external resistor. The
signal level detect circuit 3 dB optical hysteresis prevents chatter
at the signal level detect output.
Device design guarantees that the clock output frequency will
drift by less than 20% in the absence of input data transitions.
Shorting the damping factor capacitor, CD, brings the clock
output frequency to the VCO center frequency.
The AD807 consumes 170 mW and operates from a single
power supply at either +5 V or –5.2 V.
The PLL has a factory-trimmed VCO center frequency and a
frequency acquisition control loop that combine to guarantee
frequency acquisition without false lock. This eliminates a
FUNCTIONAL BLOCK DIAGRAM
CF1 CF2
PIN
QUANTIZER
+
COMPENSATING
ZERO
⌽DET
–
NIN
⌺
LOOP
FILTER
PHASE-LOCKED LOOP
VCO
THRADJ
SIGNAL
LEVEL
DETECTOR
LEVEL
DETECT
COMPARATOR/
BUFFER
CLKOUTP
FDET
CLKOUTN
RETIMING
DEVICE
+
–
DATAOUTP
DATAOUTN
AD807
SDOUT
REV. B
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2000
AD807–SPECIFICATIONS (T = T
A
Parameter
QUANTIZER–DC CHARACTERISTICS
Input Voltage Range
Input Sensitivity, VSENSE
Input Overdrive, VOD
Input Offset Voltage
Input Current
Input RMS Noise
Input Peak-to-Peak Noise
QUANTIZER–AC CHARACTERISTICS
Upper –3 dB Bandwidth
Input Resistance
Input Capacitance
Pulsewidth Distortion
LEVEL DETECT
Level Detect Range
Response Time
Hysteresis (Electrical)
SDOUT Output Logic High
SDOUT Output Logic Low
MIN to TMAX, VCC = VMIN to VMAX, CD = 0.1 F, unless
Condition
Min
@ PIN or NIN
PIN–NIN, Figure 1, BER = ≤ 1 × 10–10
Figure 1, BER = ≤ 1 × 10–10
2.5
2
0.001
BER = ≤ 1 × 10–10
BER = ≤ 1 × 10–10
RTHRESH = INFINITE
RTHRESH = 49.9 kΩ
RTHRESH = 3.4 kΩ
DC-Coupled
RTHRESH = INFINITE
RTHRESH = 49.9 kΩ
RTHRESH = 3.4 kΩ
Load = +4 mA
Load = –1.2 mA
0.8
4
14
0.1
2.3
3.0
3.0
3.6
PHASE DRIFT
JITTER
240 Bits, No Transitions
27–1 PRN Sequence
223–1 PRN Sequence
f = 10 Hz
f = 6.5 kHz
f = 65 kHz
f = 1.3 MHz
PECL OUTPUT VOLTAGE LEVELS
Output Logic High, V OH
Output Logic Low, VOL
SYMMETRY (Duty Cycle)
Recovered Clock Output, Pin 5
OUTPUT RISE / FALL TIMES
Rise Time (tR)
Fall Time (tF)
2
5
20
4.0
5.0
7.0
VCC
V
mV
V
µV
µA
µV
µV
2.5
500
10
MHz
MΩ
pF
ps
4.0
7.4
25
1.5
10.0
9.0
10.0
0.4
155
155
27–1 PRN Sequence
Figure 2
Figure 2
POWER SUPPLY VOLTAGE
POWER SUPPLY CURRENT
Unit
155.52
STATIC PHASE ERROR
SETUP TIME (tSU)
HOLD TIME (tH)
Bandwidth
Acquisition Time
CD = 0.1 µF
CD = 0.33 µF
Max
180
1
2
100
CAPTURE RANGE
TRACKING RANGE
JITTER TRANSFER
Peaking (Figure 11)
Typ
50
5
50
650
PHASE-LOCKED LOOP NOMINAL
CENTER FREQUENCY
JITTER TOLERANCE
otherwise noted.)
3.0
3.0
4
3.2
3.1
4.5
0.45
0.45
2.0
2.0
3000
7.6
1.0
0.67
65
0.08
0.04
92
CD = 0.15 µF
CD = 0.33 µF
4 × 105
2 × 106
223–1 PRN Sequence, TA = 25°C
VCC = 5 V, VEE = GND
mV
mV
mV
µs
dB
dB
dB
V
V
MHz
156
156
MHz
MHz
20
3.5
3.3
Degrees
ns
ns
40
Degrees
Degrees RMS
Degrees RMS
Unit Intervals
Unit Intervals
Unit Intervals
Unit Intervals
2.7
130
dB
dB
kHz
2 × 106
Bit Periods
Bit Periods
Volts
mA
VMIN to VMAX
VCC = 5.0 V, VEE = GND, TA = 25°C
4.5
25
34.5
5.5
39.5
VCC = 5.0 V, VEE = GND, TA = 25°C
Referenced to VCC
ρ = 1/2, TA = 25°C,
VCC = 5 V, VEE = GND
–1.2
–2.0
–1.0
–1.8
–0.7
–1.7
Volts
Volts
54.1
%
1.5
1.5
ns
ns
20%–80%
80%–20%
50.1
1.1
1.1
Specifications subject to change without notice.
–2–
REV. B
AD807
PIN FUNCTION DESCRIPTIONS
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 V
Input Voltage (Pin 12 or Pin 13) . . . . . . . . . . . . . VCC + 0.6 V
Maximum Junction Temperature . . . . . . . . . . . . . . . . . 165°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature Range (Soldering 10 sec) . . . . . . . . . 300°C
ESD Rating (Human Body Model) . . . . . . . . . . . . . . . . . 500 V
*Stresses 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
section of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
Thermal Characteristics:
16-Lead Narrow Body SOIC Package: θJA = 110°C/W.
OUTPUT
NOISE
1
0
INPUT (V)
OFFSET
OVERDRIVE
SENSITIVITY
Figure 1. Input Sensitivity, Input Overdrive
Pin
No.
Mnemonic
Description
1
DATAOUTN
Differential Retimed Data Output
2
DATAOUTP
Differential Retimed Data Output
3
VCC2
Digital VCC for ECL Outputs
4
CLKOUTN
Differential Recovered Clock Output
5
CLKOUTP
Differential Recovered Clock Output
6
VCC1
Digital VCC for Internal Logic
7
CF1
Loop Damping Capacitor
8
CF2
Loop Damping Capacitor
9
AVEE
Analog VEE
10
THRADJ
Level Detect Threshold Adjust
11
AVCC1
Analog VCC for PLL
12
NIN
Quantizer Differential Input
13
PIN
Quantizer Differential Input
14
AVCC2
Analog VCC for Quantizer
15
SDOUT
Signal Detect Output
16
VEE
Digital VEE for Internal Logic
PIN CONFIGURATION
SETUP
HOLD
tSU
tH
DATAOUTP
(PIN 2)
DATAOUTN 1
16 VEE
DATAOUTP 2
15 SDOUT
VCC2 3
CLKOUTN 4
14 AVCC2
AD807
13 PIN
TOP VIEW
CLKOUTP 5 (Not to Scale) 12 NIN
CLKOUTP
(PIN 5)
VCC1 6
Figure 2. Setup and Hold Time
CF1 7
CF2 8
11 AVCC1
10 THRADJ
9
AVEE
ORDERING GUIDE
Model
Temperature Range
Package Description
Package Option
AD807A-155BR
AD807A-155BRRL7
AD807A-155BRRL
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
16-Lead Narrowbody SOIC
750 Pieces, 7" Reel
2500 Pieces, 13" Reel
R-16A
R-16A
R-16A
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
the AD807 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. B
–3–
WARNING!
ESD SENSITIVE DEVICE
AD807
Nominal Center Frequency
DEFINITION OF TERMS
Maximum, Minimum and Typical Specifications
This is the frequency at which the VCO will oscillate with the
loop damping capacitor, CD, shorted.
Specifications for every parameter are derived from statistical
analyses of data taken on multiple devices from multiple wafer
lots. Typical specifications are the mean of the distribution of
the data for that parameter. If a parameter has a maximum (or a
minimum), that value is calculated by adding to (or subtracting
from) the mean six times the standard deviation of the distribution.
This procedure is intended to tolerate production variations: if the
mean shifts by 1.5 standard deviations, the remaining 4.5 standard
deviations still provide a failure rate of only 3.4 parts per million.
For all tested parameters, the test limits are guardbanded to
account for tester variation to thus guarantee that no device is
shipped outside of data sheet specifications.
Tracking Range
This is the range of input data rates over which the AD807 will
remain in lock.
Capture Range
This is the range of input data rates over which the AD807 will
acquire lock.
Static Phase Error
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 1.
For sufficiently large positive input voltage the output is always
Logic 1 and similarly, for negative inputs, the output is always
Logic 0. However, the transitions between output Logic Levels 1
and 0 are not at precisely defined input voltage levels, but occur
over a range of input voltages. Within this Zone of Confusion,
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 (650 µV at the 1 × 10–10
confidence level). The center of the Zone of Confusion is the
quantizer input offset voltage (± 500 µV maximum). Input Overdrive is the magnitude of signal required to guarantee correct
logic level with 1 × 10–10 confidence level.
With a single-ended PIN-TIA (Figure 3), ac coupling is used and
the inputs to the Quantizer are dc biased at some common-mode
potential. Observing the Quantizer input with an oscilloscope
probe at the point indicated shows a binary signal with 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 1, since both positive and negative offsets need to be
accommodated, the Sensitivity is twice the Overdrive. The AD807
Quantizer has 2 mV Sensitivity.
With a differential TIA (Figure 3), Sensitivity seems to improve
from observing the Quantizer input with an oscilloscope probe.
This is an illusion caused by the use of a single-ended probe. A
1 mV peak-to-peak signal appears to drive the AD807 Quantizer.
However, the single-ended probe measures only half the signal.
The true Quantizer input signal is twice this value since the
other Quantizer input is a complementary signal to the signal being observed.
Response Time
Response time is the delay between removal of the input signal
and indication of Loss of Signal (LOS) at SDOUT. The response
time of the AD807 (1.5 µs maximum) is much faster than the
SONET/SDH requirement (3 µs ≤ response time ≤ 100 µs). In
practice, the time constant of the ac coupling at the Quantizer
input determines the LOS response time.
This is the steady-state phase difference, in degrees, between the
recovered clock sampling edge and the optimum sampling instant,
which is assumed to be halfway between the rising and falling
edges of a data bit. Gate delays between the signals that define
static phase error, and IC input and output signals prohibit
direct measurement of static phase error.
Data Transition Density, ρ
This is a measure of the number of data transitions, from “0” to
“1” and from “1” to “0,” over many clock periods. ρ is the ratio
(0 ≤ ρ ≤ 1) of data transitions to bit periods.
Jitter
This is the dynamic displacement of digital signal edges from
their long term average positions, measured in degrees rms or
Unit Intervals (UI). 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.
Output Jitter
This is the jitter on the retimed data, in degrees rms, due to a
specific pattern or some pseudorandom input data sequence
(PRN Sequence).
Jitter Tolerance
Jitter Tolerance is a measure of the AD807’s ability to track a
jittery input data signal. Jitter on the input data is best thought
of as phase modulation, and is usually specified in unit intervals.
The PLL must provide a clock signal that tracks the phase
modulation in order to accurately retime jittered data. In order
for the VCO output to have a phase modulation that tracks the
input jitter, some modulation signal must be generated at the
output of the phase detector. The modulation output from the
phase detector can only be produced by a phase error between
its data input and its clock input. Hence, the PLL can never
perfectly track jittered data. However, the magnitude of the
phase error depends on the gain around the loop. At low frequencies, the integrator of the AD807 PLL provides very high
gain, and thus very large jitter can be tracked with small phase
errors between input data and recovered clock. At frequencies
closer to the loop bandwidth, the gain of the integrator is much
smaller, and thus less input jitter can be tolerated. The AD807
output will have a bit error rate less than 1 × 10–10 when in lock
and retiming input data that has the CCITT G.958 specified
jitter applied to it.
Jitter Transfer (Refer to Figure 11)
The AD807 exhibits a low-pass filter response to jitter applied to
its input data.
–4–
REV. B
AD807
POWER
COMBINER
+
Bandwidth
This describes the frequency at which the AD807 attenuates
sinusoidal input jitter by 3 dB.
PIN
+
DIFFERENTIAL
SIGNAL
SOURCE
Peaking
This describes the maximum jitter gain of the AD807 in dB.
POWER
COMBINER
+
0.47F
50⍀
NIN
–
POWER
SPLITTER
100MHz
Acquisition Time
This is the transient time, measured in bit periods, required for
the AD807 to lock onto input data from its free-running state.
75⍀
100⍀
1.0F
FILTER
5V
GND
NOISE
SOURCE
Symmetry—Recovered Clock Duty Cycle
Figure 4. Bit Error Rate vs. Signal-to-Noise Ratio
Test: Block Diagram
Symmetry is calculated as (100 × on time)/period, where on
time equals the time that the clock signal is greater than the
midpoint between its “0” level and its “1” level.
AVCC2
Bit Error Rate vs. Signal-to-Noise Ratio
AD807 Bit Error Rate vs. Signal-to-Noise Ratio performance is
shown in TPC 6. Wideband amplitude noise is summed with
the input data signal as shown in Figure 4. Performance is
shown for input data levels of 5 mV and 10 mV.
SCOPE
PROBE
D.U.T.
⌺
Damping factor, ζ describes the compensation of the second
order PLL. A larger value of ζ corresponds to more damping
and less peaking in the jitter transfer function.
EPITAXX ERM504
50⍀
AD807
Damping Factor, ζ
VCM
0.47F
⌺
400⍀
DIFFERENTIAL
INPUT
VBE
0.8V
CURRENT SOURCES
HEADROOM 0.7V
0.5mA
2mV p-p
400⍀
1mA
0.5mA
AVEE
a. Quantizer Differential Input Stage
AD807 QUANTIZER
BINARY
OUTPUT
5.9k⍀
1.2V +VBE
THRADJ
94.6k⍀
VCM
AVEE
b. Threshold Adjust
a. Single-Ended Input Application
VCC1
VCM
IOH
1mV p-p
150⍀
SDOUT
AD8015
DIFFERENTIAL
OUTPUT TIA
+OUT
SCOPE
PROBE
150⍀
IOL
AD807 QUANTIZER
VEE
BINARY
OUTPUT
–OUT
c. Signal Detect Output (SDOUT)
VCC2
VCM
450⍀
b. Differential Input Application
Figure 3. (a–b) Single-Ended and Differential Input
Applications
450⍀
DIFFERENTIAL
INPUT
2.5mA
VEE
d. PLL Differential Output Stage—DATAOUT(N),
CLKOUT(N)
Figure 5. (a–d) Simplified Schematics
REV. B
–5–
AD807–Typical Performance Characteristics
200.0E+3
35.000E–3
RTHRESH = 0⍀
180.0E+3
30.000E–3
SIGNAL DETECT LEVEL – Volts
160.0E+3
RTHRESH – ⍀
140.0E+3
120.0E+3
100.0E+3
80.0E+3
60.0E+3
40.0E+3
20.000E–3
15.000E–3
10.000E–3
RTHRESH = 49.9k⍀
5.000E–3
20.0E+3
0.0E+0
0.0
25.000E–3
RTHRESH = OPEN
5.0
10.0
15.0
20.0
25.0
SIGNAL DETECT LEVEL – mV
30.0
0.000E+0
4.4
35.0
TPC 1. Signal Detect Level vs. RTHRESH
RTHRESH = 0⍀
ELECTRICAL HYSTERESIS – dB
7.00
25.0E–3
20.0E–3
15.0E–3
10.0E–3
RTHRESH = 49.9k⍀
5.0E–3
–20
0
20
40
TEMPERATURE – ⴗC
60
80
5.00
RTHRESH = OPEN
3.00
2.00
4.6
4.8
5.0
5.2
POWER SUPPLY – V
1E–1
8.00
5E–2
3E–2
2E–2
RTHRESH = 0⍀
BIT ERROR RATE
7.00
RTHRESH = 49.9k⍀
5.00
1E–2
1 erfc
1 S
2
2 2 N
(
1278
1E–4
NSN
1279
4.00
1276
1E–8
1E–10
1E–12
0
20
40
TEMPERATURE – ⴗC
60
80
100
1277
10
TPC 3. Signal Detect Hysteresis vs. Temperature
)
1E–3
1E–5
1E–6
RTHRESH = OPEN
–20
5.6
5.4
TPC 5. Signal Detect Hysteresis vs. Power Supply
9.00
6.00
RTHRESH = 49.9k⍀
4.00
0.00
4.4
100
TPC 2. Signal Detect Level vs. Temperature
ELECTRICAL HYSTERESIS – dB
6.00
1.00
RTHRESH = OPEN
3.00
–40
5.6
5.4
8.00
RTHRESH = 0⍀
30.0E–3
SIGNAL DETECT LEVEL – Volts
4.8
5.0
5.2
SUPPLY VOLTAGE – Volts
TPC 4. Signal Detect Level vs. Supply Voltage
35.0E–3
0.0E+0
–40
4.6
12
14
16
18
S/N – dB
20
22
24
TPC 6. Bit Error Rate vs. Signal-to-Noise Ratio
–6–
REV. B
AD807
30
XFCB’s dielectric isolation allows the different blocks within
this mixed-signal IC to be isolated from each other, hence the
2 mV Sensitivity is achieved. Traditionally, high speed comparators are plagued by crosstalk between outputs and inputs, often
resulting in oscillations when the input signal approaches 10 mV.
The AD807 quantizer toggles at ± 650 µV (1.3 mV sensitivity) at
the input without making bit errors. When the input signal is
lowered below ± 650 µV, circuit performance is dominated by
input noise, and not crosstalk.
TEST CONDITIONS
WORST-CASE:
–40ⴗC, 4.5V
PERCENTAGE – %
25
20
15
10
0.1F
5
PIN 13
0
1.4
NIN 12
0.1F
1.5
1.6
1.9
2.0
1.7
1.8
RMS JITTER – Degrees
2.1
2.2
500⍀
QUANTIZER
INPUT
500⍀
OPTIONAL FILTER
2.3
50⍀
50⍀
AD807
TPC 7. Output Jitter Histogram
FERRITE BEAD
309⍀
0.1F
3.65k⍀
0.1F
50⍀
0.1F
AVCC2 14
1E+3
0.1F
+5V
AVCC1 11
JITTER TOLERANCE – UI
311MHz
NOISE
INPUT
100E+0
VCC1
CHOKE
“BIAS TEE”
10F
0.1F
6
0.1F
VCC2
10E+0
3
0.1F
AD807
Figure 6. Power Supply Noise Sensitivity Test Circuit
1E+0
0.1F
SONET MASK
500⍀
PIN 13
0.1F
100E–3
10E+0
NIN 12
100E+0
1E+3
10E+3
100E+3
FREQUENCY – Hz
1E+6
10E+6
50⍀
50⍀
AD807
TPC 8. Jitter Tolerance
500⍀
0.1F
AVCC2 14
0.1F
309⍀
3.65k⍀
3.0
QUANTIZER
INPUT
CHOKE
“BIAS TEE”
50⍀
311MHz
NOISE
INPUT
0.1F
+5V
AVCC1 11
JITTER – ns p-p
PSR – NO FILTER
VCC1
6
VCC2
3
0.1F
10F
0.1F
2.0
CMR
0.1F
Figure 7. Common-Mode Rejection Test Circuit
1.0
Signal Detect
PSR – WITH FILTER
0
0
0.1
0.2
0.3
0.4
0.5
0.7
0.6
NOISE – V p-p @ 311MHz
0.8
0.9
TPC 9. Output Jitter vs. Supply Noise and
Output Jitter vs. Common Mode Noise
THEORY OF OPERATION
Quantizer
1.0
The input to the signal detect circuit is taken from the first stage
of the quantizer. The input signal is first processed through a gain
stage. The output from the gain stage is fed to both a positive
and a negative peak detector. The threshold value is subtracted
from the positive peak signal and added to the negative peak signal.
The positive and negative peak signals are then compared. If the
positive peak, POS, is more positive than the negative peak,
NEG, the signal amplitude is greater than the threshold, and the
output, SDOUT, will indicate the presence of signal by remaining low. When POS becomes more negative than NEG, the
signal amplitude has fallen below the threshold, and SDOUT
will indicate a loss of signal (LOS) by going high. The circuit
provides hysteresis by adjusting the threshold level higher by a
factor of two when the low signal level is detected. This means
that the input data amplitude needs to reach twice the set LOS
threshold before SDOUT will signal that the data is again valid.
This corresponds to a 3 dB optical hysteresis.
The quantizer (comparator) has three gain stages, providing a
net gain of 350. The quantizer takes full advantage of the Extra
Fast Complementary Bipolar (XFCB) process. The input stage
uses a folded cascode architecture to virtually eliminate pulse
width distortion, and to handle input signals with commonmode voltage as high as the positive supply. The input offset
voltage is factory trimmed and guaranteed to be less than 500 µV.
REV. B
–7–
AD807
AD807
COMPARATOR
STAGES AND
CLOCK RECOVERY
PLL
PIN
NIN
THRESHOLD
BIAS
+
+
ITHR
A lower damping ratio allows a faster frequency acquisition;
generally the acquisition time scales directly with the capacitor
value. However, at damping ratios approaching one, the acquisition time no longer scales directly with capacitor value. The
acquisition time has two components: frequency acquisition and
phase acquisition. The frequency acquisition always scales with
capacitance, but the phase acquisition is set by the loop bandwidth of the PLL and is independent of the damping ratio.
Thus, the 0.06% fractional loop bandwidth sets a minimum
acquisition time of 2000 bit periods. Note the acquisition time
for a damping factor of one is 15,000 bit periods. This comprises
13,000 bit periods for frequency acquisition and 2,000 bit periods for phase acquisition. Compare this to the 400,000 bit
periods acquisition time specified for a damping ratio of 5; this
consists entirely of frequency acquisition, and the 2,000 bit
periods of phase acquisition is negligible.
IHYS
⌺
POSITIVE
PEAK
DETECTOR
LEVELSHIFT
DOWN
NEGATIVE
PEAK
DETECTOR
LEVELSHIFT
UP
SDOUT
Figure 8. Signal Level Detect Circuit Block Diagram
Phase-Locked Loop
The phase-locked loop recovers clock and retimes data from
NRZ data. The architecture uses a frequency detector to aid
initial frequency acquisition; refer to Figure 9 for a block diagram.
Note the frequency detector is always in the circuit. When the
PLL is locked, the frequency error is zero and the frequency
detector has no further effect. Since the frequency detector is
always in the circuit, no control functions are needed to initiate
acquisition or change mode after acquisition.
DATA
INPUT
⌽DET
S+1
⌺
While a lower damping ratio affords faster acquisition, it also
allows more peaking in the jitter transfer response (jitter peaking).
For example, with a damping ratio of 10, the jitter peaking is
0.02 dB, but with a damping ratio of 1, the peaking is 2 dB.
Center Frequency Clamp (Figure 10)
An N-channel FET circuit can be used to bring the AD807 VCO
center frequency to within ± 10% of 155 MHz when SDOUT
indicates a Loss of Signal (LOS). This effectively reduces the
frequency acquisition time by reducing the frequency error
between the VCO frequency and the input data frequency at
clamp release. The N-FET can have “on” resistance as high as
1 kΩ and still attain effective clamping. However, the chosen
N-FET should have greater than 10 MΩ “off” resistance and
less than 100 nA leakage current (source and drain) so as not to
alter normal PLL performance.
1
S
VCO
RECOVERED CLOCK
OUTPUT
FDET
RETIMING
DEVICE
RETIMED DATA
OUTPUT
Figure 9. PLL Block Diagram
The frequency detector delivers pulses of current to the charge
pump to either raise or lower the frequency of the VCO. During
the frequency acquisition process the frequency detector output
is a series of pulses of width equal to the period of the VCO.
These pulses occur on the cycle slips between the data frequency
and the VCO frequency. With a maximum density data pattern
(1010 . . . ), every cycle slip will produce a pulse at the frequency
detector output. However, with random data, not every cycle
slip produces a pulse. The density of pulses at the frequency
detector output increases with the density of data transitions. The
probability that a cycle slip will produce a pulse increases as the
frequency error approaches zero. After the frequency error has
been reduced to zero, the frequency detector output will have
no further pulses. At this point the PLL begins the process of phase
acquisition, with a settling time of roughly 2000 bit periods.
1 DATAOUTN
VEE 16
2 DATAOUTP
SDOUT 15
3 VCC2
AVCC2 14
4 CLKOUTN
PIN 13
5 CLKOUTP
NIN 12
6 VCC1
N_FET
AVCC1 11
7 CF1
CD
THRADJ 10
8 CF2
AVEE 9
AD807
Figure 10. Center Frequency Clamp Schematic
Jitter caused by variations of density of data transitions (pattern
jitter) is virtually eliminated by use of a new phase detector
(patented). Briefly, the measurement of zero phase error does
not cause the VCO phase to increase to above the average run
rate set by the data frequency. The jitter created by a 27–1
pseudorandom code is 1/2 degree, and this is small compared to
random jitter.
PEAK
0.12
0.08
0.06
0.04
0.02dB/DIV
CD
0.1
0.15
0.22
0.33
The jitter bandwidth for the PLL is 0.06% of the center frequency. This figure is chosen so that sinusoidal input jitter at
92 kHz will be attenuated by 3 dB.
The damping ratio of the PLL is user programmable with a
single external capacitor. At 155 MHz, a damping ratio of 5
is obtained with a 0.15 µF capacitor. More generally, the damping ratio scales as (fDATA × CD)1/2.
10
100
1k
FREQUENCY – Hz
10k
20k
Figure 11. Jitter Transfer vs. CD
–8–
REV. B
AD807
C1 0.1F
R1
100⍀
J1
50⍀ STRIP LINE
EQUAL LENGTH
R2
100⍀
C3 0.1F
R9
R5 100⍀ 154⍀
R10
154⍀
DATAOUTN
NOTE:
INTERCONNECTION
RUN UNDER DUT
1
DATAOUTN
VEE 16
2
DATAOUTP
SDOUT 15
3
VCC2
4
CLKOUTN
PIN 13
5
CLKOUTP
NIN 12
6
VCC1
7
CF1
R6 100⍀
DATAOUTP
J2
J3
C4 0.1F
C5 0.1F
R7 100⍀
C7
CLKOUTN
AVCC2 14
TP7
J5
TP8
SDOUT
C12
0.1F
50⍀ STRIP LINE
EQUAL LENGTH
R13
301⍀
C9
R16
C13 3.65k⍀
R15
J6
49.9⍀ 0.1F
R14
49.9⍀
PIN
R8 100⍀
CLKOUTP
J4
C6 0.1F
R3
100⍀
C8 TP1
R4
100⍀
R11
154⍀
C2
0.1F
R12
154⍀
AVCC1 11
TP2
C10
THRADJ 10
CD
8
NIN
AVEE 9
CF2
C14
0.1F
J7
TP5
RTHRESH
AD807
TP6
VECTOR PINS SPACED FOR RN55C
TYPE RESISTOR; COMPONENT
SHOWN FOR REFERENCE ONLY
VECTOR PINS SPACED THROUGH-HOLE
CAPACITOR ON VECTOR CUPS; COMPONENT
SHOWN FOR REFERENCE ONLY
NOTES:
C7–C10 ARE 0.1F BYPASS
CAPACITORS
RIGHT ANGLE SMA CONNECTOR
OUTER SHELL TO GND PLANE
C11
10F
TP3
5V
TP4
GND
ALL RESISTORS ARE 1% 1/8 WATT
SURFACE MOUNT
TPxO TEST POINTS ARE VECTORBOARD
K24A/M PINS
Figure 12. Evaluation Board Schematic
CIRCUIT SIDE
08-002901-02
REV A
INT2
08-002901-08
REV A
INT1
08-002901-07
REV A
SILKSCREEN TOP
08-002901-03
REV A
COMPONENT SIDE
08-002901-01
REV A
SOLDERMASK TOP
08-002901-04
REV A
Figure 13. Evaluation Board Pictorials
REV. B
–9–
AD807
C1 0.1F
R1
100⍀
J1
R2
100⍀
C2 0.1F
SDOUT
TP7
R9
R5 100⍀ 154⍀
R10
154⍀
DATAOUTN
1
DATAOUTN
VEE 16
2
DATAOUTP
SDOUT 15
3
VCC2
4
CLKOUTN
5
CLKOUTP
6
VCC1
7
CF1
THRADJ 10
8
CF2
AVEE 9
R6 100⍀
DATAOUTP
J2
J3
C3 0.1F
C4 0.1F
R7 100⍀
C7
CLKOUTN
R17
3.65k⍀
C13
0.1F
R16
301⍀
C12
2.2F
C11
R14
50⍀
AVCC2 14
R15
50⍀
PIN 13
R8 100⍀
CLKOUTP
J4
C5 0.1F
R3
100⍀
C8 TP1
R4
100⍀
R11
154⍀
C2
0.1F
R12
154⍀
C10
CD
TP2
AD807
C9
10F
TP4
NOTES:
1. ALL CAPACITORS ARE CHIP,
15pF ARE MICA.
2. 150nH ARE SMT
3. C7, C8, C10, C11 ARE 0.1F
BYPASS CAPACITORS
NIN 12
AVCC1 11
ABB HAFO 1A227
FC HOUSING
0.8A/W, 0.7pF
2.5GHz
0.01F
C15
0.1F
C14
0.1F
0.1F
TP3
5V
1 NC
50⍀
LINE
10F
+VS 8
2 IIN
+OUT 7
3 NC
–OUT 6
4 VBYP
0.1F
TP6
R13
THRADJ
TP5
50⍀
LINE
150nH
15pF
15pF
150nH
–VS 5
AD8015
NC = NO CONNECT
Figure 14. Low Cost 155 Mbps Fiber Optic Receiver Schematic
Table I. AD807—AD8015 Fiber Optic Receiver Circuit:
Output Bit Error Rate and Output Jitter vs. Input Power
Average Optical
Input Power
(dBm)
Output Bit
Error Rate
–6.4
–6.5
–6.6
–6.7
Loses Lock
7.5 × 10–3
9.4 × 10–4
0 × 10–14
–7.0 to –35.5
–36.0
0 × 10–14
3 × 10–12
–36.5
–37.0
–38.0
–39.0
–39.2
–39.3
4.8 × 10–10
2.8 × 10–8
1.3 × 10–5
1.0 × 10–3
1.9 × 10–3
Loses Lock
503mV
Output Jitter
(ps rms)
100mV/
DIV
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