AD ADCLK854 1.8 v, 12-lvds/24-cmos output, low power clock fanout buffer Datasheet

1.8 V, 12-LVDS/24-CMOS Output,
Low Power Clock Fanout Buffer
ADCLK854
FEATURES
FUNCTIONAL BLOCK DIAGRAM
2 selectable differential inputs
Selectable LVDS/CMOS outputs
Up to 12 LVDS (1.2 GHz) or 24 CMOS (250 MHz) outputs
<12 mW per channel (100 MHz operation)
54 fs rms integrated jitter (12 kHz to 20 MHz)
100 fs rms additive broadband jitter
2.0 ns propagation delay (LVDS)
135 ps output rise/fall (LVDS)
70 ps output-to-output skew (LVDS)
Sleep mode
Pin programmable control
1.8 V power supply
ADCLK854
VREF
VS/2
LVDS/
CMOS
OUT0 (OUT0B)
CLK0
OUT1 (OUT1A)
CLK0
OUT1 (OUT1B)
CLK1
OUT2 (OUT2A)
CLK1
OUT2 (OUT2B)
IN_SEL
OUT3 (OUT3A)
CTRL_A
OUT3 (OUT3B)
LVDS/
CMOS
APPLICATIONS
OUT4 (OUT4B)
OUT5 (OUT5A)
The ADCLK854 offers two selectable inputs and a sleep mode
feature. The IN_SEL pin state determines which input is fanned
out to all the outputs. The SLEEP pin enables a sleep mode to
power down the device.
OUT5 (OUT5B)
CTRL_B
OUT6 (OUT6A)
OUT6 (OUT6B)
OUT7 (OUT7A)
OUT7 (OUT7B)
GENERAL DESCRIPTION
The ADCLK854 is a 1.2 GHz/250 MHz LVDS/CMOS fanout
buffer optimized for low jitter and low power operation. Possible
configurations range from 12 LVDS to 24 CMOS outputs,
including combinations of LVDS and CMOS outputs. Three
control lines are used to determine whether fixed blocks of
outputs (three banks of four) are LVDS or CMOS outputs.
OUT4 (OUT4A)
LVDS/
CMOS
OUT8 (OUT8A)
OUT8 (OUT8B)
OUT9 (OUT9A)
OUT9 (OUT9B)
CTRL_C
OUT10 (OUT10A)
OUT10 (OUT10B)
SLEEP
OUT11 (OUT11A)
OUT11 (OUT11B)
07218-001
Low jitter clock distribution
Clock and data signal restoration
Level translation
Wireless communications
Wired communications
Medical and industrial imaging
ATE and high performance instrumentation
OUT0 (OUT0A)
Figure 1.
The inputs accept various types of single-ended and differential
logic levels including LVPECL, LVDS, HSTL, CML, and CMOS.
Table 8 provides interface options for each type of connection.
This device is available in a 48-pin LFCSP package. It is specified
for operation over the standard industrial temperature range of
−40°C to +85°C.
Rev. 0
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
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One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2009 Analog Devices, Inc. All rights reserved.
ADCLK854
TABLE OF CONTENTS
Features .............................................................................................. 1
Typical Performance Characteristics ..............................................9
Applications ....................................................................................... 1
Functional Description .................................................................. 12
General Description ......................................................................... 1
Clock Inputs ................................................................................ 12
Functional Block Diagram .............................................................. 1
AC-Coupled Input Applications............................................... 12
Revision History ............................................................................... 2
Clock Outputs ............................................................................. 12
Specifications..................................................................................... 3
Control and Function Pins........................................................ 13
Electrical Characteristics ............................................................. 3
Power Supply............................................................................... 13
Timing Characteristics ................................................................ 4
Applications Information .............................................................. 14
Clock Characteristics ................................................................... 5
Logic and Power Characteristics ................................................ 5
Using the ADCLK854 Outputs for ADC Clock Applications
....................................................................................................... 14
Absolute Maximum Ratings............................................................ 6
LVDS Clock Distribution .......................................................... 14
Determining Junction Temperature .......................................... 6
CMOS Clock Distribution ........................................................ 14
ESD Caution .................................................................................. 6
Input Termination Options ....................................................... 15
Thermal Performance .................................................................. 6
Outline Dimensions ....................................................................... 16
Pin Configuration and Function Descriptions ............................. 7
Ordering Guide .......................................................................... 16
REVISION HISTORY
4/09—Revision 0: Initial Version
Rev. 0 | Page 2 of 16
ADCLK854
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
Typical (Typ) values are given for VS = 1.8 V and TA = 25°C, unless otherwise noted. Minimum (Min) and maximum (Max) values are given over
the full VS = 1.8 V ± 5% and TA = −40°C to +85°C variation, unless otherwise noted. Input slew rate > 1 V/ns, unless otherwise noted.
Table 1. Clock Inputs and Outputs
Parameter
CLOCK INPUTS
Input Frequency
Input Sensitivity, Differential
Symbol
Min
Typ
0
Input Resistance (Differential)
Input Capacitance
Input Bias Current (Each Pin)
LVDS CLOCK OUTPUTS
Output Frequency
Output Voltage Differential
Delta VOD
Offset Voltage
Delta VOS
Short-Circuit Current
Unit
1200
MHz
mV p-p
150
Input Level
Input Common-Mode Voltage
Input Common-Mode Range
Input Voltage Offset
Input Sensitivity, Single-Ended
Max
VCM
VCMR
VS/2 − 0.1
0.4
1.8
V p-p
VS/2 + 0.5
VS − 0.4
V
V
mV
mV p-p
30
150
7
2
CIN
−350
VOD
ΔVOD
VOS
ΔVOS
ISA, ISB
247
344
1.125
1.25
3
+350
kΩ
pF
μA
1200
454
50
1.375
50
6
MHz
mV
mV
V
mV
mA
CMOS CLOCK OUTPUTS
Jitter performance improves with higher slew
rates (greater voltage swing)
Larger voltage swings can turn on the protection
diodes and degrade jitter performance
Inputs are self-biased; enables ac coupling
Inputs dc-coupled with 200 mV p-p signal applied
CLKx ac-coupled; CLKx ac bypassed to ground
Full input swing
Termination = 100 Ω; differential (OUTx, OUTx)
See Figure 9 for swing vs. frequency
Each pin (output shorted to GND)
Single-ended; termination = open; OUTx and
OUTx in phase
Output Frequency
Output Voltage High
Output Voltage Low
Output Voltage High
Output Voltage Low
Reference Voltage
Output Voltage
Output Resistance
Output Current
Conditions
Differential input
250
VOH
VOL
VOH
VOL
VREF
VS − 0.1
0.1
VS − 0.35
0.35
VS/2 − 0.1
VS/2
60
VS/2 + 0.1
500
Rev. 0 | Page 3 of 16
MHz
V
V
V
V
V
Ω
μA
With 10 pF load per output; see Figure 16 for
swing vs. frequency
@ 1 mA load
@ 1 mA load
@ 10 mA load
@ 10 mA load
±500 μA
ADCLK854
TIMING CHARACTERISTICS
Table 2. Timing Characteristics
Parameter
LVDS OUTPUTS
Output Rise/Fall Time
Propagation Delay, Clock-to-LVDS Output
Temperature Coefficient
Output Skew 1
LVDS Outputs in the Same Bank
All LVDS Outputs
On the Same Part
Across Multiple Parts
Additive Time Jitter
Integrated Random Jitter
Symbol
Min
Typ
Max
Unit
tR , tF
tPD
1.5
135
2.0
2.0
235
2.7
ps
ns
ps/°C
50
ps
65
390
ps
ps
54
74
86
150
260
Broadband Random Jitter 2
Crosstalk Induced Jitter
CMOS OUTPUTS
Output Rise/Fall Time
Propagation Delay, Clock-to-CMOS Output
Temperature Coefficient
Output Skew1
CMOS Outputs in the Same Bank
All CMOS Outputs
On the Same Part
Across Multiple Parts
Additive Time Jitter
Integrated Random Jitter
Broadband Random Jitter2
Crosstalk Induced Jitter
LVDS-TO-CMOS OUTPUT SKEW 3
LVDS Output(s) and CMOS Output(s) on the
Same Part
tR, tF
tPD
2.5
525
3.2
2.2
fs rms
fs rms
fs rms
fs rms
fs rms
BW = 12 kHz to 20 MHz; clock = 1000 MHz
BW = 50 kHz to 80 MHz; clock = 1000 MHz
BW = 10Hz to 100 MHz; clock = 1000 MHz
Input slew = 1 V/ns, see Figure 11
Calculated from spur energy with an
interferer 10 MHz offset from the carrier
950
4.2
ps
ns
ps/°C
20% to 80%; CLOAD = 10 pF
10 pF load
155
ps
175
640
ps
ps
56
100
260
0.8
1
1.6
fs rms
fs rms
fs rms
BW = 12 kHz to 20 MHz; clock = 200 MHz
Input slew = 2 V/ns, see Figure 11
Calculated from spur energy with an
interferer 10 MHz offset from the carrier
ns
CMOS load = 10 pF and LVDS load = 100 Ω
This is the difference between any two similar delay paths while operating at the same voltage and temperature.
Calculated from the SNR of the ADC method.
3
Measured at the rising edge of the clock signal.
2
Rev. 0 | Page 4 of 16
Conditions
Termination = 100 Ω differential; 3.5 mA
20% to 80% measured differentially
VICM = VREF, VID = 0.5 V
ADCLK854
CLOCK CHARACTERISTICS
Table 3. Clock Output Phase Noise
Parameter
CLOCK-TO-LVDS ABSOLUTE PHASE NOISE
1000 MHz
Min
CLOCK-TO-CMOS ABSOLUTE PHASE NOISE
200 MHz
Typ
Max
Unit
−90
−108
−117
−126
−135
−141
−146
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
−101
−119
−127
−138
−147
−153
−156
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
Conditions
Input slew rate > 1 V/ns
@ 10 Hz offset
@ 100 Hz offset
@ 1 kHz offset
@ 10 kHz offset
@ 100 kHz offset
@ 1 MHz offset
@ 10 MHz offset
Input slew rate > 1 V/ns
@ 10 Hz offset
@ 100 Hz offset
@ 1 kHz offset
@ 10 kHz offset
@ 100 kHz offset
@ 1 MHz offset
@ 10 MHz offset
LOGIC AND POWER CHARACTERISTICS
Table 4. Control Pin Characteristics
Parameter
CONTROL PINS (IN_SEL, CTRL_x, SLEEP) 1
Logic 1 Voltage
Logic 0 Voltage
Logic 1 Current
Logic 0 Current
Capacitance
POWER
Supply Voltage Requirement
LVDS Outputs
LVDS @ 100 MHz
LVDS @ 1200 MHz
Symbol
Min
VIH
VIL
IIH
IIL
VS − 0.4
5
−5
Typ
Max
Unit
8
0.4
20
+5
V
V
μA
μA
pF
1.8
1.89
V
84
175
100
215
mA
mA
115
265
140
325
3
mA
mA
mA
2
VS
1.71
CMOS Outputs
CMOS @ 100 MHz
CMOS @ 250 MHz
SLEEP
Power Supply Rejection 2
LVDS
CMOS
PSR t PD
0.9
ps/mV
PSR t PD
1.2
ps/mV
1
These pins each have a 200 kΩ internal pull-down resistor.
2
Change in tPD per change in VS.
Rev. 0 | Page 5 of 16
Conditions
VS = 1.8 V ± 5%
Full operation
All outputs enabled as LVDS and loaded, RL = 100 Ω
All outputs enabled as LVDS and loaded, RL = 100 Ω
Full operation
All outputs enabled as CMOS and loaded, CL = 10 pF
All outputs enabled as CMOS and loaded, CL = 10 pF
SLEEP pin pulled high; does not include power dissipated
in the external resistors
ADCLK854
ABSOLUTE MAXIMUM RATINGS
DETERMINING JUNCTION TEMPERATURE
Table 5.
Parameter
Supply Voltage
VS to GND
Inputs
CLKx and CLKx
Rating
CMOS Inputs
Outputs
Maximum Voltage
Voltage Reference Voltage (VREF)
Operating Temperature
Ambient Range
Junction
Storage Temperature Range
−0.3 V to +2 V
To determine the junction temperature on the application
printed circuit board (PCB), use the following equation:
TJ = TCASE + (ΨJT × PD)
2V
where:
TJ is the junction temperature (°C).
TCASE is the case temperature (°C) measured by the user at the
top center of the package.
ΨJT is from Table 6.
PD is the power dissipation.
−0.3 V to +2 V
−0.3 V to +2 V
−0.3 to +2 V
Values of θJA are provided for package comparison and PCB
design considerations. θJA can be used for a first-order approximation of TJ by the equation
−40°C to +85°C
150°C
−65°C to +150°C
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.
TJ = TA + (θJA × PD)
where TA is the ambient temperature (°C).
Values of θJB are provided in Table 6 for package comparison
and PCB design considerations.
ESD CAUTION
THERMAL PERFORMANCE
Table 6.
Parameter
Junction-to-Ambient Thermal Resistance
Still Air
0.0 m/sec Air Flow
Moving Air
1.0 m/sec Air Flow
2.5 m/sec Air Flow
Junction-to-Board Thermal Resistance
Moving Air
1.0 m/sec Air Flow
Junction-to-Case Thermal Resistance
Moving Air
Die-to-Heat Sink
Junction-to-Top-of-Package Characterization Parameter
Still Air
0 m/sec Air Flow
1
Symbol
Description (Using a 2S2P Test Board)
Value 1
Unit
42
°C/W
37
33
°C/W
°C/W
26
°C/W
2
°C/W
0.5
°C/W
θJA
Per JEDEC JESD51-2
θJMA
Per JEDEC JESD51-6
θJB
Per JEDEC JESD51-8
θJC
Per MIL-STD 883, Method 1012.1
ΨJT
Per JEDEC JESD51-2
Results are from simulations. The PCB is a JEDEC multilayer type. Thermal performance for actual applications requires careful inspection of the conditions in the
application to determine if they are similar to those assumed in these calculations.
Rev. 0 | Page 6 of 16
ADCLK854
48
47
46
45
44
43
42
41
40
39
38
37
OUT0 (OUT0A)
OUT0 (OUT0B)
OUT1 (OUT1A)
OUT1 (OUT1B)
GND
VS
OUT2 (OUT2A)
OUT2 (OUT2B)
OUT3 (OUT3A)
OUT3 (OUT3B)
GND
VS
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
VREF
CLK0
1
2
ADCLK854
TOP VIEW
(Not to Scale)
36
35
34
33
NC
NC
OUT4 (OUT4A)
OUT4 (OUT4B)
32
31
30
29
28
27
26
25
OUT5 (OUT5A)
OUT5 (OUT5B)
VS
GND
OUT6 (OUT6A)
OUT6 (OUT6B)
OUT7 (OUT7A)
OUT7 (OUT7B)
NOTES:
1. NC = NO CONNECT.
2. EXPOSED PADDLE MUST BE CONNECTED TO GND.
07218-002
CTRL_C
SLEEP
OUT10 (OUT10B)
OUT10 (OUT10A)
GND
VS
OUT9 (OUT9B)
OUT9 (OUT9A)
OUT8 (OUT8B)
OUT8 (OUT8A)
GND
VS
13
14
15
16
17
18
19
20
21
22
23
24
CLK0 3
GND 4
CLK1 5
CLK1 6
VS 7
OUT11 (OUT11B) 8
OUT11 (OUT11A) 9
IN_SEL 10
CTRL_A 11
CTRL_B 12
PIN 1
INDICATOR
Figure 2. Pin Configuration
Table 7. Pin Function Descriptions
Pin No.
1
2
Mnemonic
VREF
CLK0
Description
Reference Voltage.
Input (Negative) 0.
3
7, 18, 24, 30,
37, 43
5
CLK0
VS
Input (Positive) 0.
Supply Voltage.
CLK1
Input (Negative) 1.
6
8
CLK1
OUT11 (OUT11B)
Input (Positive) 1.
Complementary Side of Differential LVDS Output 11, or CMOS Output 11 on Channel B.
9
10
OUT11 (OUT11A)
IN_SEL
True Side of Differential LVDS Output 11, or CMOS Output 11 on Channel A.
Input Select. (0 = CLK0, CLK0; 1 = CLK1, CLK1). CMOS logic input with 200 kΩ pull-down resistor.
11
12
13
14
15
CTRL_A
CTRL_B
CTRL_C
SLEEP
OUT10 (OUT10B)
Control for Output 3 to Output 0 (0 = LVDS, 1 = CMOS). CMOS logic input with 200 kΩ pull-down resistor.
Control for Output 7 to Output 4 (0 = LVDS, 1 = CMOS). CMOS logic input with 200 kΩ pull-down resistor.
Control for Output 11 to Output 8 (0 = LVDS, 1 = CMOS). CMOS logic input with 200 kΩ pull-down resistor.
Sleep Mode Control (0 = normal operation, 1 = sleep). CMOS logic input with 200 kΩ pull down resistor.
Complementary Side of Differential LVDS Output 10, or CMOS Output 10 on Channel B.
16
4, 17, 23, 29,
38, 44
19
OUT10 (OUT10A)
GND
True Side of Differential LVDS Output 10, or CMOS Output 10 on Channel A.
Ground Pin.
OUT9 (OUT9B)
Complementary Side of Differential LVDS Output 9, or CMOS Output 9 on Channel B.
20
21
OUT9 (OUT9A)
OUT8 (OUT8B)
True Side of Differential LVDS Output 9, or CMOS Output 9 on Channel A.
Complementary Side of Differential LVDS Output 8, or CMOS Output 8 on Channel B.
22
25
OUT8 (OUT8A)
OUT7 (OUT7B)
True Side of Differential LVDS Output 8, or CMOS Output 8 on Channel A.
Complementary Side of Differential LVDS Output 7, or CMOS Output 7 on Channel B.
Rev. 0 | Page 7 of 16
ADCLK854
Pin No.
26
27
Mnemonic
OUT7 (OUT7A)
OUT6 (OUT6B)
Description
True Side of Differential LVDS Output 7, or CMOS Output 7 on Channel A.
Complementary Side of Differential LVDS Output 6, or CMOS Output 6 on Channel B.
28
31
OUT6 (OUT6A)
OUT5 (OUT5B)
True Side of Differential LVDS Output 6, or CMOS Output 6 on Channel A.
Complementary Side of Differential LVDS Output 5, or CMOS Output 5 on Channel B.
32
33
OUT5 (OUT5A)
OUT4 (OUT4B)
True Side of Differential LVDS Output 5, or CMOS Output 5 on Channel A.
Complementary Side of Differential LVDS Output 4, or CMOS Output 4 on Channel B.
34
35
36
39
OUT4 (OUT4A)
NC
NC
OUT3 (OUT3B)
True Side of Differential LVDS Output 4, or CMOS Output 4 on Channel A.
No Connect.
No Connect.
Complementary Side of Differential LVDS Output 3, or CMOS Output 3 on Channel B.
40
41
OUT3 (OUT3A)
OUT2 (OUT2B)
True Side of Differential LVDS Output 3, or CMOS Output 3 on Channel A.
Complementary Side of Differential LVDS Output 2, or CMOS Output 2 on Channel B.
42
45
OUT2 (OUT2A)
OUT1 (OUT1B)
True Side of Differential LVDS Output 2, or CMOS Output 2 on Channel A.
Complementary Side of Differential LVDS Output 1, or CMOS Output 1 on Channel B.
46
47
OUT1 (OUT1A)
OUT0 (OUT0B)
True Side of Differential LVDS Output 1, or CMOS Output 1 on Channel A.
Complementary Side of Differential LVDS Output 0, or CMOS Output 0 on Channel B.
48
(49)
OUT0 (OUT0A)
EPAD
True Side of Differential LVDS Output 0, or CMOS Output 0 on Channel A.
Exposed Paddle. The exposed paddle must be connected to GND.
Rev. 0 | Page 8 of 16
ADCLK854
TYPICAL PERFORMANCE CHARACTERISTICS
VS = +1.8 V, TA = 25°C, unless otherwise noted.
2
M 200ps 10.0GS/s
CH1
–36.0mV
CH2 100mV
Figure 3. LVDS Output Waveform @ 1200 MHz
M 1.0ns 10.0GS/s
CH1
–36.0mV
07218-006
CH2 100mV
07218-003
2
Figure 6. LVDS Output Waveform @ 200 MHz
2.3
2.4
2.3
2.2
PROPAGATION DELAY (ns)
PROPATATION DELAY (ns)
2.2
2.1
2.0
1.9
2.1
2.0
1.9
1.8
1.7
1.6
1.8
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
INPUT DIFFERENTIAL (V p-p)
1.4
200
07218-004
1.7
0.1
800
1000
1200
1400
1600
Figure 7. LVDS Propagation Delay vs. VICM
715
DIFFERENTIAL OUTPUT SWING (mV p-p)
54
53
52
51
50
49
48
47
0
200
400
600
800
1000
FREQUENCY (MHz)
1200
07218-005
46
Figure 5. LVDS Output Duty Cycle vs. Frequency
705
695
685
675
1.62
1.72
1.82
POWER SUPPLY (V)
1.92
07218-008
55
DUTY CYCLE (%)
600
INPUT COMMON-MODE (mV)
Figure 4. LVDS Propagation Delay vs. Input Differential Voltage (VID)
45
400
07218-007
1.5
Figure 8. LVDS Differential Output Swing vs. Power Supply Voltage
Rev. 0 | Page 9 of 16
ADCLK854
–80
ABSOLUTE PHASE NOISE MEASURED @ 1GHz WITH AGILENT
E5052 USING WENZEL CLOCK SOURCE CONSISTING OF A
WENZEL 100MHz CRYSTAL OSCILLATOR (P/N 500-06672),
WENZEL 5× MULTIPLIER (P/N LNOM-100-5-13-14-F-A), AND A
WENZEL 2× MULTIPLIER (P/N LNDD-500-14-14-1-D).
–90
–100
PHASE NOISE (dBc/Hz)
800
700
600
–110
ADCLK854
–120
–130
–140
–150
CLOCK SOURCE
–160
500
100
1k
10k
100k
1M
Figure 9. LVDS Differential Output Swing vs. Input Frequency
300
325
ALL BANKS CMOS
300
250
275
2 BANKS CMOS
1 BANK LVDS
250
225
CURRENT (mA)
200
175
150
125
200
150
100
100
1 BANK CMOS
2 BANKS LVDS
75
50
50
0
200
400
600
800
1000
1200
1400
1600
1800
FREQUENCY (MHz)
0
25
07218-110
0
54
400
53
350
52
DUTY CYCLE (%)
55
450
300
250
200
46
INPUT SLEW RATE (V/ns)
2.5
07218-011
47
50
2.0
175
200
225
250
49
100
1.5
150
50
48
1.0
125
51
150
0.5
100
Figure 13. LVDS/CMOS Current vs. Frequency with Various Logic
Combinations
500
0
75
FREQUENCY (MHz)
Figure 10. LVDS Current vs. Frequency; All Banks Set to LVDS
0
50
07218-113
ALL BANKS LVDS
25
Figure 11. Additive Broadband Jitter vs. Input Slew Rate
45
0
50
100
150
200
250
FREQUENCY (MHz)
Figure 14. CMOS Output Duty Cycle vs. Frequency (10 pF Load)
Rev. 0 | Page 10 of 16
07218-014
CURRENT (mA)
100M
Figure 12. Absolute Phase Noise LVDS @ 1000 MHz
350
JITTER (fs rms)
10M
FREQUENCY OFFSET (Hz)
07218-012
1700
INPUT FREQUENCY (MHz)
–180
10
07218-009
1600
1500
1400
1300
1200
1100
900
1000
800
700
600
500
400
100
300
–170
400
200
DIFFERENTIAL OUTPUT SWING (mV p-p)
900
ADCLK854
CH1 300mV
1.25ns/DIV
CH1
954mV
CH1 300mV
Figure 15. CMOS Output Waveform @ 200 MHz (10 pF Load)
5.0ns/DIV
954mV
Figure 18. CMOS Output Waveform @ 50 MHz (10 pF Load)
1.9
1.8
1.8
RLOAD = 750Ω
25°C
RLOAD = 1kΩ
1.7
OUTPUT SWING (V)
1.7
OUTPUT SWING (V)
CH1
07218-018
1
07218-015
1
1.6
85°C
1.5
1.4
1.3
1.6
RLOAD = 500Ω
RLOAD = 300Ω
1.5
100
150
200
250
FREQUENCY (MHz)
Figure 16. CMOS Output Swing vs. Frequency by Temperature (10 pF Load)
2.0
1.9
CL = 5pF
1.7
CL = 10pF
1.6
1.5
CL = 20pF
1.4
1.3
1.2
1.1
1.0
0
50
100
150
200
250
FREQUENCY (MHz)
07218-017
OUTPUT SWING (V)
1.8
Figure 17. CMOS Output Swing vs. Frequency by Capacitive Load
Rev. 0 | Page 11 of 16
1.4
0
50
100
150
200
250
FREQUENCY (MHz)
Figure 19. CMOS Output Swing vs. Frequency by Resistive Load
07218-019
1.1
50
07218-016
1.2
ADCLK854
FUNCTIONAL DESCRIPTION
The ADCLK854 accepts a clock input from one of two inputs
and distributes the selected clock to all output channels. The
outputs are grouped into three banks of four and can be set to
either LVDS or CMOS levels. This allows the selection of multiple logic configurations ranging from 12 LVDS to 24 CMOS
outputs, along with other combinations using both types of logic.
CLOCK INPUTS
The ADCLK854 differential inputs are internally self-biased.
The clock inputs have a resistor divider that sets the commonmode level for the inputs. The complementary inputs are biased
about 30 mV lower than the true input to avoid oscillations if
the input signal stops. See Figure 20 for the equivalent input
circuit.
The inputs can be ac-coupled or dc-coupled. Table 8 displays a
guide for input logic compatibility. A single-ended input can be
accommodated by ac or dc coupling to one side of the differential
input; bypass the other input to ground with a capacitor.
The second option allows the use of the VREF pin to set the dc
bias level for the ADCLK854. The VREF pin can be connected to
CLKx and CLKx through resistors. This method allows lower
impedance termination of signals at the ADCLK854 (for more
information, see Figure 32). The internal bias resistors remain
in parallel with the external biasing. However, the relatively
high impedance of the internal resistors allows the external
termination to VREF to dominate. This method is also useful
when offsetting the inputs; using only the internal biasing, as
previously mentioned, is not desirable.
CLOCK OUTPUTS
Each driver consists of a differential LVDS output or two singleended CMOS outputs (always in phase). When the LVDS driver
is enabled, the corresponding CMOS driver is in tristate; when
the CMOS driver is enabled, the corresponding LVDS driver is
powered down and tristated. Figure 21 and Figure 22 display
the equivalent output stage.
VS
Note that jitter performance degrades with low input slew rate,
as shown in Figure 11. See Figure 27 through Figure 32 for
different termination schemes.
3.5mA
OUTx
VS
9kΩ
OUTx
9.5kΩ
CLKx
8.5kΩ
GND
07218-021
10kΩ 10kΩ
07218-020
CLKx
9kΩ
3.5mA
Figure 21. LVDS Output Simplified Equivalent Circuit
Figure 20. ADCLK854 Input Stage
VS
VS
AC-COUPLED INPUT APPLICATIONS
The ADCLK854 offers two options for ac coupling. The first
option requires no external components (excluding the dc
blocking capacitor), it allows the user to simply couple the
reference signal onto the clock input pins. For more information, see Figure 29.
OUTB
07218-022
OUTA
Figure 22. CMOS Output Equivalent Circuit
Table 8. Input Logic Compatibility
Supply (V)
3.3
2.5
1.8
3.3
2.5
1.8
1.5
3.3
2.5
1.8
Logic
CML
CML
CML
CMOS
CMOS
CMOS
HSTL
LVDS
LVPECL
LVPECL
LVPECL
Common Mode (V)
2.9
2.1
1.4
1.65
1.25
0.9
0.75
1.25
2.0
1.2
0.5
Output Swing (V)
0.8
0.8
0.8
3.3
2.5
1.8
0.75
0.4
0.8
0.8
0.8
Rev. 0 | Page 12 of 16
AC-Coupled
Yes
Yes
Yes
Not allowed
Not allowed
Yes
Yes
Yes
Yes
Yes
Yes
DC-Coupled
Not allowed
Not allowed
Yes
Not allowed
Not allowed
Yes
Yes
Yes
Not allowed
Yes
Yes
ADCLK854
CONTROL AND FUNCTION PINS
CTRL_A—Logic Select
This pin selects either CMOS (high) or LVDS (low) logic for
Output 3, Output 2, Output 1, and Output 0. This pin has an
internal 200 kΩ pull-down resistor.
CTRL_B—Logic Select
This pin selects either CMOS (high) or LVDS (low) logic for
Output 7, Output 6, Output 5, and Output 4. This pin has an
internal 200 kΩ pull-down resistor.
CTRL_C—Logic Select
This pin selects either CMOS (high) or LVDS (low) logic for
Output 11, Output 10, Output 9, and Output 8. This pin has an
internal 200 kΩ pull-down resistor.
with adequate capacitance (>10 μF), and bypassing all power
pins with adequate capacitance (0.1 μF) as close to the part as
possible. The layout of the ADCLK854 evaluation board
(ADCLK854/PCBZ) provides a good layout example.
Exposed Metal Paddle
The exposed metal paddle on the ADCLK854 package is an
electrical connection as well as a thermal enhancement. For the
device to function properly, the paddle must be properly
attached to ground (GND). The ADCLK854 dissipates heat
through its exposed paddle. The PCB acts as a heat sink for the
ADCLK854. The PCB attachment must provide a good thermal
path to a larger heat dissipation area, such as the ground plane
on the PCB. This requires a grid of vias from the top layer down
to the ground plane. See Figure 23 for an example.
IN_SEL—Clock Input Select
A logic low selects CLK0 and CLK0 whereas a logic high selects
CLK1 and CLK1. This pin has an internal 200 kΩ pull-down
resistor.
VIAS TO GND PLANE
Sleep mode powers down the chip except for the internal band
gap. The input is active high, which puts the outputs into a
high-Z state. This pin has a 200 kΩ pull-down resistor.
07218-023
Sleep Mode
Figure 23. PCB Land for Attaching Exposed Paddle
POWER SUPPLY
The ADCLK854 requires a 1.8 V ± 5% power supply for VS. Best
practice recommends bypassing the power supply on the PCB
Rev. 0 | Page 13 of 16
ADCLK854
APPLICATIONS INFORMATION
USING THE ADCLK854 OUTPUTS FOR ADC CLOCK
APPLICATIONS
Any high speed, analog-to-digital converter (ADC) is extremely
sensitive to the quality of the sampling clock provided by the
user. An ADC can be thought of as a sampling mixer, and any
noise, distortion, or timing jitter on the clock is combined with
the desired signal at the analog-to-digital output. Clock integrity
requirements scale with the analog input frequency and resolution, with higher analog input frequency applications at ≥14-bit
resolution being the most stringent. The theoretical SNR of an
ADC is limited by the ADC resolution and the jitter on the
sampling clock. Considering an ideal ADC of infinite resolution
where the step size and quantization error can be ignored, the
available SNR can be expressed approximately by
LVDS CLOCK DISTRIBUTION
The ADCLK854 provides clock outputs that are selectable as
either CMOS or LVDS level outputs. LVDS is a differential
output option that uses a current-mode output stage. The
nominal current is 3.5 mA, which yields 350 mV output swing
across a 100 Ω resistor. The LVDS output meets or exceeds all
ANSI/TIA/EIA-644 specifications. A recommended termination
circuit for the LVDS outputs is shown in Figure 25.
If ac coupling is necessary, place decoupling capacitors either before
or after the 100 Ω termination resistor. See Application Note
AN-586 at www.analog.com for more information on LVDS.
VS
VS
LVDS
LVDS
07218-025
⎡ 1 ⎤
SNR = 20 × log ⎢
⎥
⎣⎢ 2πf ATJ ⎥⎦
100Ω
100Ω
DIFFERENTIAL (COUPLED)
Figure 25. LVDS Output Termination
where fA is the highest analog frequency being digitized and TJ
is the rms jitter on the sampling clock.
CMOS CLOCK DISTRIBUTION
Figure 24 shows the required sampling clock jitter as a function
of the analog frequency and effective number of bits (ENOB).
For more information, see Application Note AN-756 and
Application Note AN-501 at www.analog.com.
The output drivers of the ADCLK854 can be configured as
CMOS drivers. When selected as a CMOS driver, each output
becomes a pair of CMOS outputs. These outputs are 1.8 V
CMOS compatible.
1
SNR = 20log 2πf T
A J
100
When single-ended CMOS clocking is used, some of the
following guidelines apply.
18
16
Design point-to-point connections such that each driver has only
one receiver, if possible. Connecting outputs in this manner allows
for simple termination schemes and minimizes ringing due to
possible mismatched impedances on the output trace. Series termination at the source is generally required to provide transmission
line matching and/or to reduce current transients at the driver.
90
TJ =
100
fS
200
14
fS
400
f
70
S
12
1ps
60
2ps
10
10p
s
8
50
40
ENOB
SNR (dB)
80
100
fA FULL-SCALE SINE WAVE ANALOG FREQUENCY (MHz)
1k
07218-024
6
30
10
The value of the resistor (typically 10 Ω to 100 Ω) is dependent
on the board design and timing requirements. CMOS outputs
are also limited in terms of the capacitive load or trace length
that they can drive. Typically, trace lengths less than 3 inches are
recommended to preserve signal rise/fall times and signal integrity.
Figure 24. SNR and ENOB vs. Analog Input Frequency
Many high performance ADCs feature differential clock inputs
to simplify the task of providing the required low jitter clock on
a noisy PCB. Distributing a single-ended clock on a noisy PCB
can result in coupled noise on the sample clock. Differential
distribution has inherent common-mode rejection that can
provide superior clock performance in a noisy environment.
Consider the input requirements of the ADC (differential or
single-ended, logic level, and termination) when selecting the
best clocking/converter solution.
CMOS
10Ω
60.4Ω
1.0 INCH
CMOS
MICROSTRIP
07218-026
110
Figure 26. Series Termination of CMOS Output
Termination at the far end of the PCB trace is a second option.
The CMOS outputs of the ADCLK854 do not supply enough
current to provide a full voltage swing with a low impedance
resistive, far end termination, as shown in Figure 27. The far end
termination network should match the PCB trace impedance and
provide the desired switching point. The reduced signal swing may
Rev. 0 | Page 14 of 16
ADCLK854
still meet receiver input requirements in some applications. This
can be useful when driving long trace lengths on less critical
networks.
CLK
CLK
50Ω
VS
50Ω
10Ω
VCC – 2V
100Ω
CMOS
07218-027
CMOS
50Ω
100Ω
CLK
CLK
Figure 27. CMOS Output with Far End Termination
50Ω
50Ω
CLK
CLK
INPUT TERMINATION OPTIONS
CLK
CLK
07218-030
Because of the limitations of single-ended CMOS clocking,
consider using differential outputs when driving high speed
signals over long traces. The ADCLK854 offers LVDS outputs
that are better suited for driving long traces wherein the inherent
noise immunity of differential signaling provides superior
performance for clocking converters.
VCC – 2V
Figure 30. Typical AC-Coupled or DC-Coupled PECL Configuration
(See Table 8 for LVPECL DC-Coupling Limitations)
For single-ended operation always bypass unused input to
GND, as shown in Figure 31.
CLK
CLK
CLK
07218-031
Figure 32 illustrates the use of VREF to provide low impedance
termination into VS/2. In addition, a way to negate the 30 mV
input offset is with external resistor values; for example, using a
1.8 V CMOS with long traces to provide far end termination.
Figure 31. Typical 1.8 V CMOS Configurations for Short Trace Lengths
(See Table 8 for CMOS Compatibility)
100Ω
CLK
VREF
CLK
07218-028
100Ω
CLK
Figure 32. Use of VREF to Provide Low Impedance Termination into VS/2
Figure 28. Typical AC-Coupled or DC-Coupled LVDS or HSTL Configuration
(See Table 8 for More Information)
VCC
CLK
CLK
VCC
07218-029
CLK
CLK
07218-032
CLK
CLK
Figure 29. Typical AC-Coupled or DC-Coupled CML Configuration
(See Table 8 for CML Coupling Limitations)
Rev. 0 | Page 15 of 16
ADCLK854
OUTLINE DIMENSIONS
0.30
0.23
0.18
0.60 MAX
0.60 MAX
37
36
PIN 1
INDICATOR
6.75
BSC SQ
48
1
0.50
BSC
*2.90
2.80 SQ
2.70
EXPOSED
PAD
(BOTTOM VIEW)
25
24
TOP VIEW
1.00
0.85
0.80
12° MAX
0.80 MAX
0.65 TYP
0.50
0.40
0.30
13
12
0.20 MIN
5.50 REF
0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.20 REF
SEATING
PLANE
PIN 1
INDICATOR
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
*COMPLIANT TO JEDEC STANDARDS MO-220-VKKD-2
WITH EXCEPTION TO EXPOSED PAD DIMENSION.
080508-A
7.00
BSC SQ
Figure 33. 48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
7 mm × 7 mm Body, Very Thin Quad
CP-48-6
Dimensions shown in millimeters
ORDERING GUIDE
Model
ADCLK854BCPZ 1
ADCLK854BCPZ-REEL71
ADCLK854/PCBZ1
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
Package Description
48-Lead LFCSP_VQ
48-Lead LFCSP_VQ
Evaluation Board
Z = RoHS Compliant Part.
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D07218-0-4/09(0)
Rev. 0 | Page 16 of 16
Package Option
CP-48-6
CP-48-6