Multirate to 2.7 Gb/s Clock and Data Recovery IC with Integrated Limiting Amp ADN2819 FEATURES PRODUCT DESCRIPTION Meets SONET requirements for jitter transfer/generation/tolerance Quantizer sensitivity: 4 mV typical Adjustable slice level: ±100 mV 1.9 GHz minimum bandwidth Patented clock recovery architecture Loss of signal detect range: 3 mV to 15 mV Single reference clock frequency for all rates, including 15/14 (7%) wrapper rate Choice of 19.44 MHz, 38.88 MHz, 77.76 MHz, or 155.52 MHz REFCLK LVPECL/LVDS/LVCMOS/LVTTL compatible inputs (LVPECL/LVDS only at 155.52 MHz) 19.44 MHz oscillator on-chip to be used with external crystal Loss of lock indicator Loopback mode for high speed test data Output squelch and bypass features Single-supply operation: 3.3 V Low power: 540 mW typical 7 mm × 7 mm 48-lead LFCSP The ADN2819 provides the receiver functions of quantization, signal level detect, and clock and data recovery at rates of OC-3, OC-12, OC-48, Gigabit Ethernet, and 15/14 FEC rates. 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. The device is intended for WDM system applications, and can be used with either an external reference clock or an on-chip oscillator with external crystal. Both native rates and 15/14 rate digital wrappers are supported by the ADN2819, without any change of reference clock. 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 front end signal detect circuit indicates when the input signal level has fallen below a user-adjustable threshold. The signal detect circuit has hysteresis to prevent chatter at the output. APPLICATIONS SONET OC-3/-12/-48, SDH STM-1/-4/-16, GbE and 15/14 FEC rates WDM transponders Regenerators/repeaters Test equipment Backplane applications The ADN2819 is available in a compact 7 mm × 7 mm, 48-lead chip scale package. FUNCTIONAL BLOCK DIAGRAM SLICEP/N 2 VCC VEE CF1 ADN2819 CF2 LOL LOOP FILTER 2 PIN 2 QUANTIZER NIN PHASE SHIFTER PHASE DET. LOOP FILTER VCO FREQUENCY LOCK DETECTOR /n REFSEL[0..1] REFCLKP/N XO1 XTAL OSC XO2 LEVEL DETECT DATA RETIMING DIVIDER 1/2/4/16 3 2 THRADJ SDOUT DATAOUTP/N 2 CLKOUTP/N REFSEL 02999-0-001 VREF FRACTIONAL DIVIDER SEL[0..2] Figure 1. 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 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. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved. ADN2819 TABLE OF CONTENTS Specifications..................................................................................... 3 Limiting Amplifier ..................................................................... 14 Absolute Maximum Ratings............................................................ 6 Slice Adjust .................................................................................. 14 Thermal Characteristics .............................................................. 6 Loss of Signal (LOS) Detector .................................................. 14 ESD Caution.................................................................................. 6 Reference Clock.......................................................................... 14 Pin Configuration and Function Descriptions............................. 7 Lock Detector Operation .......................................................... 15 Definition of Terms.......................................................................... 9 Squelch Mode ............................................................................. 16 Maximum, Minimum, and Typical Specifications ................... 9 Test Modes: Bypass and Loopback........................................... 16 Input Sensitivity and Input Overdrive....................................... 9 Applications Information .............................................................. 17 Single-Ended vs. Differential ...................................................... 9 PCB Design Guidelines ............................................................. 17 LOS Response Time ................................................................... 10 Choosing AC-Coupling Capacitors ......................................... 19 Jitter Specifications..................................................................... 10 DC-Coupled Application .......................................................... 20 Theory of Operation ...................................................................... 12 LOL Toggling During Loss of Input Data............................... 20 Functional Description .................................................................. 14 Outline Dimensions ....................................................................... 21 Multirate Clock and Data Recovery......................................... 14 Ordering Guide .......................................................................... 21 REVISION HISTORY 5/04—Data Sheet Changed from Rev. A to Rev. B Updated Format..............................................................Universal Changes to Specifications ............................................................ 3 Changes to Table 7 and Table 8................................................. 15 Updated Outline Dimensions ................................................... 21 Changes to Ordering Guide ...................................................... 21 1/03—Data Sheet Changed from Rev. 0 to Rev. A Changes to Table IV ................................................................... 12 Updated OUTLINE DIMENSIONS ........................................ 16 Rev. B | Page 2 of 24 ADN2819 SPECIFICATIONS Table 1. TA = TMIN to TMAX, VCC = VMIN to VMAX, VEE = 0 V, CF = 4.7 µF, SLICEP = SLICEN = VCC, unless otherwise noted. Parameter QUANTIZER—DC CHARACTERISTICS Input Voltage Range Peak-to-Peak Differential Input Input Common-Mode Level Differential Input Sensitivity Input Overdrive Input Offset Input rms Noise QUANTIZER—AC CHARACTERISTICS Upper –3 dB Bandwidth Small Signal Gain S11 Input Resistance Input Capacitance Pulse Width Distortion2 QUANTIZER SLICE ADJUSTMENT Gain Control Voltage Range Slice Threshold Offset LEVEL SIGNAL DETECT (SDOUT) Level Detect Range (See Figure 4) Response Time Hysteresis (Electrical) Conditions Min @ PIN or NIN, dc-coupled 0 DC-coupled (See Figure 28) PIN-NIN, ac-coupled1, BER = 1 × 10–10 See Figure 8 0.4 4 2 500 244 BER = 1 × 10–10 Max Unit 1.2 2.4 V V V mV p-p mV p-p µV µV rms 10 5 1.9 54 –15 100 0.65 10 Differential @ 2.5 GHz Differential SLICEP–SLICEN = ±0.5 V SLICEP–SLICEN @ SLICEP or SLICEN Typ 0.11 –0.8 1.3 0.20 GHz dB dB Ω pF ps 0.30 +0.8 VCC V/V V V mV ±1.0 RTHRESH = 2 Ω RTHRESH = 20 kΩ RTHRESH = 90 kΩ DC-coupled OC-48, PRBS 223 RTHRESH = 2 kΩ RTHRESH = 20 kΩ RTHRESH = 90 kΩ OC-12, PRBS 223 RTHRESH = 2 kΩ RTHRESH = 20 kΩ RTHRESH = 90 kΩ RTHRESH = 90 kΩ @ 25°C OC-3, PRBS 223 RTHRESH = 2 kΩ RTHRESH = 20 kΩ RTHRESH = 90 kΩ RTHRESH = 90 kΩ @ 25°C OC-48, PRBS 27 RTHRESH = 2 kΩ RTHRESH = 20 kΩ RTHRESH = 90 kΩ OC-12, PRBS 27 RTHRESH = 2 kΩ RTHRESH = 20 kΩ RTHRESH = 90 kΩ Rev. B | Page 3 of 24 9.4 2.5 0.7 0.1 13.3 5.3 3.0 0.3 18.0 7.6 5.2 5 mV mV mV µs 5.6 3.9 3.2 6.6 6.2 6.7 7.8 8.5 9.9 dB dB dB 4.7 1.8 6.4 6.0 6.3 6.9 7.8 10.0 dB dB dB dB 4.8 3.6 8.9 3.4 6.2 5.6 5.6 6.6 8.5 9.9 dB dB dB dB 5.6 3.9 3.2 6.6 6.2 6.7 7.8 8.5 9.9 dB dB dB 5.7 3.9 3.2 6.6 6.2 6.7 7.8 8.5 9.9 dB dB dB ADN2819 Parameter Hysteresis (Electrical) (continued) LOSS OF LOCK DETECTOR (LOL) Loss of Lock Response Time POWER SUPPLY VOLTAGE POWER SUPPLY CURRENT PHASE-LOCKED LOOP CHARACTERISTICS Jitter Transfer BW Jitter Peaking Jitter Generation Conditions OC-3, PRBS 27 RTHRESH = 2 kΩ RTHRESH = 20 kΩ RTHRESH = 90 kΩ Min Typ Max Unit 5.4 4.6 3.9 6.6 6.4 6.8 7.7 8.2 9.7 dB dB dB 3.0 150 60 3.3 164 3.6 215 mV V mA From fVCO error > 1000 ppm PIN–NIN = 10 mV p-p OC-48 GbE OC-12 OC-3 OC-48 OC-12 OC-3 OC-48, 12 kHz–20 MHz 590 310 140 48 0.025 0.004 0.002 0.05 OC-12, 12 kHz–5 MHz 0.02 OC-3, 12 kHz–1.3 MHz 0.02 Jitter Tolerance CML OUTPUTS (CLKOUTP/N, DATAOUTP/N) Single-Ended Output Swing Differential Output Swing Output High Voltage Output Low Voltage Rise Time Fall Time OC-48 (See Figure 14) 600 Hz3 6 kHz3 100 kHz 1 MHz3 GbE (OC-24) (See Figure 14) 300 Hz3 3 kHz3 50 kHz 500 kHz3 OC-12 (See Figure 14) 30 Hz3 300 Hz 25 kHz 250 kHz3 OC-3 (See Figure 14) 30 Hz3 300 Hz3 6500 Hz 65 kHz3 VSE (See Figure 7) VDIFF (See Figure 7) VOH VOL, referred to VCC 20%–80% 80%–20% Rev. B | Page 4 of 24 880 480 200 85 0.003 0.09 0.002 0.04 0.002 0.04 kHz kHz kHz kHz dB dB dB UI rms UI p-p UI rms UI p-p UI rms UI p-p 92 20 5.5 1.0 UI p-p UI p-p UI p-p UI p-p 16 16 7.7 2.2 UI p-p UI p-p UI p-p UI p-p 100 44 5.8 1.0 UI p-p UI p-p UI p-p UI p-p 50 23.5 6.0 1.0 UI p-p UI p-p UI p-p UI p-p 300 600 –0.60 455 910 VCC 600 1200 –0.30 150 150 mV mV V V ps ps ADN2819 Parameter Setup Time Hold Time REFCLK DC INPUT CHARACTERISTICS Input Voltage Range Peak-to-Peak Differential Input Common-Mode Level TEST DATA DC INPUT CHARACTERISTICS4 (TDINP/N) Peak-to-Peak Differential Input Voltage LVTTL DC INPUT CHARACTERISTICS Input High Voltage Input Low Voltage Input Current Input Current (SEL0 and SEL1 Only)5 LVTTL DC OUTPUT CHARACTERISTICS Output High Voltage Output Low Voltage Conditions TS (See Figure 3) OC-48 GbE OC-12 OC-3 TH (See Figure 3) OC-48 GbE OC-12 OC-3 @ REFCLKP or REFCLKN Min VOH, IOH = –2.0 mA VOL, IOL = +2.0 mA 1 PIN and NIN should be differentially driven, ac-coupled for optimum sensitivity. PWD measurement made on quantizer outputs in bypass mode. 3 Jitter tolerance measurements are equipment limited. 4 TDINP/N are CML inputs. If the drivers to the TDINP/N inputs are anything other than CML, they must be ac-coupled. 5 SEL0 and SEL1 have internal pull-down resistors, causing higher IIH. 2 Rev. B | Page 5 of 24 Max Unit 140 350 750 3145 ps ps ps ps 150 350 750 3150 ps ps ps ps 0 100 DC-coupled, single-ended CML inputs VIH VIL VIN = 0.4 V or VIN = 2.4 V VIN = 0.4 V or VIN = 2.4 V Typ 2.0 –5 –5 VCC VCC/2 V mV V 0.8 V V 0.8 +5 +50 V µA µA 0.4 V V 2.4 ADN2819 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Supply Voltage (VCC) Minimum Input Voltage (All Inputs) Maximum Input Voltage (All Inputs) Maximum Junction Temperature Storage Temperature Lead Temperature (Soldering 10 sec) THERMAL CHARACTERISTICS Rating 5.5 V VEE – 0.4 V VCC + 0.4 V 165°C –65°C to +150°C 300°C Thermal Resistance 48-lead LFCSP, 4-layer board with exposed paddle soldered to VCC θJA = 25°C/W 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. 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. B | Page 6 of 24 ADN2819 48 LOOPEN 47 VCC 46 VEE 45 SDOUT 44 BYPASS 43 VEE 42 VEE 41 CLKOUTP 40 CLKOUTN 39 SQUELCH 38 DATAOUTP 37 DATAOUTN PIN CONFIGURATION AND FUNCTION DESCRIPTIONS ADN2819 TOPVIEW 36 VCC 35 VCC 34 VEE 33 VEE 32 SEL0 31 SEL1 30 SEL2 29 VEE 28 VCC 27 VEE 26 VCC 25 CF2 02999-B-002 PIN 1 INDICATOR REFCLKN 13 REFCLKP 14 REFSEL 15 VEE 16 TDINP 17 TDINN 18 VEE 19 VCC 20 CF1 21 VEE 22 REFSEL1 23 REFSEL0 24 THRADJ 1 VCC 2 VEE 3 VREF 4 PIN 5 NIN 6 SLICEP 7 SLICEN 8 VEE 9 LOL 10 XO1 11 XO2 12 Figure 2. 48-Lead LFCSP Pin Configuration Table 3. Pin Function Descriptions Pin Number 1 2, 26, 28, Pad 3, 9, 16, 19, 22, 27, 29, 33, 34, 42, 43, 46 4 5 6 7 8 10 11 12 13 14 15 17 18 20, 47 21 23 24 25 30 31 32 35, 36 37 38 39 40 41 44 45 48 1 Mnemonic THRADJ VCC VEE Type1 AI P P Description LOS Threshold Setting Resistor. Analog Supply. Ground. VREF PIN NIN SLICEP SLICEN LOL XO1 XO2 REFCLKN REFCLKP REFSEL TDINP TDINN VCC CF1 REFSEL1 REFSEL0 CF2 SEL2 SEL1 SEL0 VCC DATAOUTN DATAOUTP SQUELCH CLKOUTN CLKOUTP BYPASS SDOUT LOOPEN AO AI AI AI AI DO AO AO DI DI DI AI AI P AO DI DI AO DI DI DI P DO DO DI DO DO DI DO DI Internal VREF Voltage. Decouple to GND with 0.1 µF capacitor. Differential Data Input. Differential Data Input. Differential Slice Level Adjust Input. Differential Slice Level Adjust Input. Loss of Lock Indicator. LVTTL active high. Crystal Oscillator. Crystal Oscillator. Differential REFCLK Input. LVTTL, LVCMOS, LVPECL, LVDS (LVPECL, LVDS only at 155.52 MHz). Differential REFCLK Input. LVTTL, LVCMOS, LVPECL, LVDS (LVPECL, LVDS only at 155.52 MHz). Reference Source Select. 0 = on-chip oscillator with external crystal; 1 = external clock source, LVTTL. Differential Test Data Input. CML. Differential Test Data Input. CML. Digital Supply. Frequency Loop Capacitor. Reference Frequency Select (See Table 6) LVTTL. Reference Frequency Select (See Table 6) LVTTL. Frequency Loop Capacitor. Data Rate Select (See Table 5) LVTTL. Data Rate Select (See Table 5) LVTTL. Data Rate Select (See Table 5) LVTTL. Output Driver Supply. Differential Retimed Data Output. CML. Differential Retimed Data Output. CML. Disable Clock and Data Outputs. Active high. LVTTL. Differential Recovered Clock Output. CML. Differential Recovered Clock Output. CML. Bypass CDR Mode. Active high. LVTTL. Loss of Signal Detect Output. Active high. LVTTL. Enable Test Data Inputs. Active high. LVTTL. Type: P = Power, AI = Analog Input, AO = Analog Output, DI = Digital Input, DO = Digital Output. Rev. B | Page 7 of 24 ADN2819 CLKOUTP TH 02999-B-003 TS DATAOUTP/N Figure 3. Output Timing 18 THRADJ RESISTOR VS. LOS TRIP POINT 16 14 12 mV 10 8 6 02999-B-004 4 2 0 10 0 20 30 40 50 60 RESISTANCE (kΩ) 70 80 90 100 Figure 4. LOS Comparator Trip Point Programming 10 18 9 16 8 14 FREQUENCY 12 6 5 4 8 02999-B-006 4 2 2 1 0 1 2 3 4 5 6 7 HYSTERESIS (dB) 8 9 10 0 0 1 2 3 4 5 6 7 8 Figure 5. LOS Hysteresis OC-3, –40°C, 3.6 V, 223 – 1 PRBS Input Pattern, RTH = 90 kΩ Figure 6. LOS Hysteresis OC-12, –40°C, 3.6 V, 223 – 1 PRBS Input Pattern, RTH = 90 kΩ OUTP VCML VSE OUTN OUTP–OUTN VSE 0V 9 HYSTERESIS (dB) VDIFF 02999-B-007 0 10 6 3 02999-B-005 FREQUENCY 7 Figure 7. Single-Ended vs. Differential Output Specifications Rev. B | Page 8 of 24 10 ADN2819 DEFINITION OF TERMS MAXIMUM, MINIMUM, AND TYPICAL SPECIFICATIONS SINGLE-ENDED VS. DIFFERENTIAL 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 and therefore guarantee that no device is shipped outside of data sheet specifications. AC-coupling is typically used to drive the inputs to the quantizer. The inputs are internally dc biased to a commonmode potential of ~0.6 V. Driving the ADN2819 single-ended and observing the quantizer input with an oscilloscope probe at the point indicated in Figure 9 shows a binary signal with an average value equal to the common-mode potential and instantaneous values above and below the average value. It is convenient to measure the peak-to-peak amplitude of this signal and to call the minimum required value the quantizer sensitivity. Referring to Figure 8, since both positive and negative offsets need to be accommodated, the sensitivity is twice the overdrive. 10mV p-p VREF INPUT SENSITIVITY AND INPUT OVERDRIVE SCOPE PROBE 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 8. For a 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 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. The center of the zone of confusion 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. PIN + QUANTIZER 50Ω 50Ω 02999-B-009 VREF Figure 9. Single-Ended Sensitivity Measurement 5mV p-p VREF SCOPE PROBE OUTPUT ADN2819 PIN NOISE 1 ADN2819 + QUANTIZER NIN 50Ω 0 50Ω INPUT (V p-p) OVERDRIVE SENSITIVITY (2× OVERDRIVE) Figure 8. Input Sensitivity and Input Overdrive 02999-B-008 OFFSET 02999-B-010 VREF Figure 10. Differential Sensitivity Measurement Driving the ADN2819 differentially (see Figure 10), sensitivity seems to improve by 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 ADN2819 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 complementary to the signal being observed. Rev. B | Page 9 of 24 ADN2819 LOS RESPONSE TIME 0.1 JITTER GAIN (dB) The LOS response time is the delay between the removal of the input signal and indication of loss of signal (LOS) at SDOUT. The ADN2819’s response time is 300 ns typ when the inputs are dc-coupled. In practice, the time constant of ac-coupling at the quantizer input determines the LOS response time. SLOPE = –20dB/DECADE ACCEPTABLE RANGE The following sections summarize the specifications of the 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 ADN2819 performance with respect to those specifications. Jitter Generation 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 OC-48 devices, the band-pass filter has a 12 kHz high-pass cutoff frequency, with a roll-off of 20 dB/decade and a low-pass cutoff frequency of at least 20 MHz. The jitter generated should be less than 0.01 UI rms and 0.1 UI p-p. Figure 11. Jitter Transfer Curve Jitter Tolerance Jitter tolerance is defined as the peak-to-peak amplitude of the sinusoidal jitter applied on the input signal that causes a 1 dB power penalty. This is a stress test that is intended to ensure no additional penalty is incurred under the operating conditions (see Figure 12). Figure 13 shows the typical OC-48 jitter tolerance performance of the ADN2819. 15 SLOPE = –20dB/DECADE 1.5 0.15 f0 f1 f2 f3 02999-B-012 Jitter is the dynamic displacement of digital signal edges from their long-term average positions measured in UI (unit intervals), 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. fC JITTER FREQUENCY (kHz) INPUT JITTER AMPLITUDE (UI) The ADN2819 CDR is designed to achieve the best bit-errorrate (BER) performance, and has exceeded the jitter transfer, generation, and tolerance specifications proposed for SONET/SDH equipment defined in the Telcordia Technologies specification. 02999-B-011 JITTER SPECIFICATIONS f4 JITTER FREQUENCY (Hz) Figure 12. SONET Jitter Tolerance Mask 100 Jitter Transfer ADN2819 10 1 OC-48 SONET MASK 0.1 1 10 100 1k 10k 100k MODULATION FREQUENCY (Hz) Figure 13. OC-48 Jitter Tolerance Curve Rev. B | Page 10 of 24 1M 10M 02999-B-013 AMPLITUDE (UI p- p) Jitter transfer function is the ratio of the jitter on the output signal to the jitter applied on the input signal versus the frequency. This parameter measures the limited amount of jitter on an input signal that can be transferred to the output signal (see Figure 11). ADN2819 OC3_JIT_TOLERANCE GBE_JIT_TOLERANCE OC3_JIT_TRANSFER GBE_JIT_TRANSFER OC12_JIT_TOLERANCE OC48_JIT_TOLERANCE OC12_JIT_TRANSFER OC48_JIT_TRANSFER 0.5 0 –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 –3.5 –4.0 –4.5 –5.0 –5.5 –6.0 –6.5 –7.0 –7.5 –8.0 –8.5 –9.0 –10.0 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M 02999-B-014 –9.5 Figure 14. Jitter Transfer and Jitter Tracking BW Table 4. Jitter Transfer and Tolerance: SONET Spec vs. ADN2819 Rate OC-48 OC-12 OC-3 1 Jitter Transfer ADN2819 Implementation SONET Spec (fC) (kHz) Margin 2 MHz 590 3.4 500 kHz 140 3.6 130 kHz 48 2.7 Mask Corner Frequency 1 MHz 250 kHz 65 kHz Jitter tolerance measurements limited by test equipment capabilities. Rev. B | Page 11 of 24 ADN2819 4.8 MHz 4.8 MHz 600 kHz Jitter Tolerance SONET Spec ADN2819 (UI p-p) (UI p-p) 0.15 1.0 0.15 1.0 0.15 1.0 Implementation Margin1 6.67 6.67 6.67 ADN2819 THEORY OF OPERATION The delay- and phase-locked loops together track the phase of the input data signal. For example, when the clock lags 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 data. The faster clock picks up phase while the delayed data loses phase. Since the loop filter is an integrator, the static phase error is driven to zero. Another view of the circuit is that the phase shifter implements the zero required for the frequency compensation of a secondorder phase-locked loop. This zero is placed in the feedback path and therefore 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. Since this circuit has no zero in the closed-loop transfer, jitter peaking is minimized. The delay- and phase-locked loops together simultaneously provide wideband jitter accommodation and narrow-band jitter filtering. The linearized block diagram in Figure 15 shows that the jitter transfer function, Z(s)/X(s), is a second-order low-pass providing excellent filtering. Note that the jitter transfer has no zero, unlike an ordinary second-order phase-locked loop. This means the main PLL loop has low jitter peaking (see Figure 16), which makes this circuit ideal for signal regenerator applications where jitter peaking in a cascade of regenerators can contribute to hazardous jitter accumulation. psh 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 = cn n psh X(s) s2 +s +1 do o TRACKING ERROR TRANSFER FUNCTION e(s) = X(s) s2 + s s2 do d psh + cn c 02999-B-015 The ADN2819 is a delay-locked 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 that 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 the input jitter. A separate phase control loop, comprised of the VCO, tracks the low frequency components of the input jitter. The initial frequency of the VCO is set by a third loop that compares the VCO frequency with the reference frequency and sets the coarse tuning voltage. The jitter tracking phase-locked loop controls the VCO by the fine tuning control. Figure 15. PLL/DLL Architecture The error transfer, e(s)/X(s), has the same high-pass form as an ordinary phase-locked loop. This transfer function is free to be optimized to give excellent wideband jitter accommodation since the jitter transfer function, Z(s)/X(s), provides the narrowband jitter filtering. See Table 4 for error transfer bandwidths and jitter transfer bandwidths at the various data rates. The delay-locked and phase-locked 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, so the phase shifter remains close to the center of its range, and therefore contributes little to the low frequency jitter accommodation. At medium jitter frequencies, the gain and tuning range of the VCO are not large enough to track the input jitter. In this case, the VCO control voltage becomes large and saturates, and the VCO frequency dwells at one or the other 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; thus, 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. Rev. B | Page 12 of 24 ADN2819 Rev. B | Page 13 of 24 JITTER PEAKING IN ORDINARY PLL JITTER GAIN (dB) ADN2819 Z(s) X(s) o n psh d psh c f (kHz) Figure 16. Jitter Response vs. Conventional PLL 02999-B-016 The gain of the loop integrator is small for high jitter frequencies, so larger phase differences are needed to make the loop control voltage big enough to tune the range of the phase shifter. Large phase errors at high jitter frequencies cannot be tolerated. In this region, the gain of the integrator determines the jitter accommodation. Since 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 5 MHz for OC-12, OC-48, and GbE data rates, and 600 kHz for OC-3 data rates. ADN2819 FUNCTIONAL DESCRIPTION MULTIRATE CLOCK AND DATA RECOVERY The ADN2819 will recover clock and data from serial bit streams at OC-3, OC-12, OC-48, and GbE data rates as well as the 15/14 FEC rates. The output of the 2.5 GHz VCO is divided down in order to support the lower data rates. The data rate is selected by the SEL[2..0] inputs (see Table 5). Table 5. Data Rate Selection SEL[2..0] 000 001 010 011 100 101 110 111 Rate OC-48 GbE OC-12 OC-3 OC-48 FEC GbE FEC OC-12 FEC OC-3 FEC Frequency (MHz) 2488.32 1250.00 622.08 155.52 2666.06 1339.29 666.51 166.63 Note that it is not expected to use both LOS and slice adjust at the same time. Systems with optical amplifiers need the slice adjust to evade ASE. However, a loss of signal in an optical link that uses optical amplifiers causes the optical amplifier output to be full-scale noise. Under this condition, the LOS would not detect the failure. In this case, the loss of lock signal indicates the failure because the CDR circuitry is unable to lock onto a signal that is full-scale noise. REFERENCE CLOCK There are three options for providing the reference frequency to the ADN2819: differential clock, single-ended clock, or crystal oscillator. See Figure 17, Figure 18, and Figure 19 for example configurations. ADN2819 REFCLKP BUFFER LIMITING AMPLIFIER The limiting amplifier has differential inputs (PIN/NIN) that are internally terminated with 50 Ω to an on-chip voltage reference (VREF = 0.6 V typically). These inputs are normally ac-coupled, although dc-coupling is possible as long as the input common-mode voltage remains above 0.4 V (see Figure 26, Figure 27, and Figure 28 in the Applications Information section). Input offset is factory trimmed to achieve better than 4 mV typical sensitivity with minimal drift. The limiting amplifier can be driven differentially or single-ended. REFCLKN 100kΩ 100kΩ VCC/2 VCC XO1 XO2 VCC CRYSTAL OSCILLATOR 02999-B-017 VCC REFSEL Figure 17. Differential REFCLK Configuration SLICE ADJUST ADN2819 VCC REFCLKP CLK OSC OUT BUFFER REFCLKN NC LOSS OF SIGNAL (LOS) DETECTOR 100kΩ The receiver front end level signal detect circuit indicates when the input signal level has fallen below a user adjustable threshold. The threshold is set with a single external resistor from Pin 1, THRADJ, to GND. The LOS comparator trip point versus the resistor value is illustrated in Figure 4 (this is only valid for SLICEP = SLICEN = VCC). If the input level to the ADN2819 drops below the programmed LOS threshold, SDOUT (Pin 45) will indicate the loss of signal condition with a Logic 1. The LOS response time is ~300 ns by design, but it is dominated by the RC time constant in ac-coupled applications. If the LOS detector is used, the quantizer slice adjust pins must both be tied to VCC. This is to avoid interaction with the LOS threshold level. Rev. B | Page 14 of 24 100kΩ VCC/2 VCC VCC VCC XO1 XO2 CRYSTAL OSCILLATOR REFSEL Figure 18. Single-Ended REFCLK Configuration 02999-B-018 The quantizer slicing level can be offset by ±100 mV to mitigate the effect of amplified spontaneous emission (ASE) noise by applying a differential voltage input of ±0.8 V to SLICEP/N inputs. If no adjustment of the slice level is needed, SLICEP/N should be tied to VCC. ADN2819 An on-chip oscillator to be used with an external crystal is also provided as an alternative to using the REFCLKN/P inputs. Details of the recommended crystal are given in Table 7. ADN2819 VCC REFCLKP Table 7. Required Crystal Specifications BUFFER Parameter Mode Frequency/Overall Stability Frequency Accuracy Temperature Stability Aging ESR NC REFCLKN 100kΩ VCC/2 XO1 XO2 CRYSTAL OSCILLATOR 02999-B-019 19.44MHz REFSEL REFSEL must be tied to VCC when the REFCLKN/P inputs are active, or tied to VEE when the oscillator is used. No connection between the XO pin and the REFCLK input is necessary (see Figure 17, Figure 18, and Figure 19). Note that the crystal should operate in series resonant mode, which renders it insensitive to external parasitics. No trimming capacitors are required. Figure 19. Crystal Oscillator Configuration The ADN2819 can accept any of the following reference clock frequencies: 19.44 MHz, 38.88 MHz, and 77.76 MHz at LVTTL/ LVCMOS/LVPECL/LVDS levels, or 155.52 MHz at LVPECL/ LVDS levels via the REFCLKN/P inputs, independent of data rate (including Gigabit Ethernet and wrapper rates). The input buffer accepts any differential signal with a peak-to-peak differential amplitude of greater than 100 mV (e.g., LVPECL or LVDS) or a standard single-ended low voltage TTL input, providing maximum system flexibility. The appropriate division ratio can be selected using the REFSEL0/1 pins, according to Table 6. Phase noise and duty cycle of the reference clock are not critical, and 100 ppm accuracy is sufficient. LOCK DETECTOR OPERATION The lock detector monitors the frequency difference between the VCO and the reference clock, and deasserts the loss of lock signal when the VCO is within 500 ppm of center frequency. This enables the phase loop, which then maintains phase lock, unless the frequency error exceeds 0.1%. Should this occur, the loss of lock signal is reasserted and control returns to the frequency loop, which will reacquire and maintain a stable clock signal at the output. The frequency loop requires a single external capacitor between CF1 and CF2. The capacitor specification is given in Table 8. Table 6. Reference Frequency Selection REFSEL 1 1 1 1 0 REFSEL[1..0] 00 01 10 11 XX Applied Reference Frequency (MHz) 19.44 38.88 77.76 155.52 REFCLKP/N Inactive. Use 19.44 MHz XTAL on Pins XO1, XO2 (pull REFCLKP to VCC) Table 8. Recommended CF Capacitor Specification Parameter Temperature Range Capacitance Leakage Rating Value –40°C to +85°C >3.0 µF <80 nA >6.3 V LOL 1 1000 500 0 500 Figure 20. Transfer Function LOL Rev. B | Page 15 of 24 1000 fVCO ERROR (ppm) 02999-B-020 100kΩ Value Series Resonant 19.44 MHz ± 100 ppm ±100 ppm ±100 ppm ±100 ppm 50 Ω max ADN2819 ADN2819 PIN + 0 QUANTIZER NIN CDR 50Ω 50Ω VREF 1 FROM QUANTIZER OUTPUT 1 50Ω RETIMED DATA CLK 0 50Ω TDINP/N LOOPEN BYPASS DATAOUTP/N CLKOUTP/N SQUELCH 02999-B-021 VCC Figure 21. Test Modes SQUELCH MODE When the squelch input is driven to a TTL high state, the clock and data outputs are set to the zero state to suppress downstream processing. If desired, this pin can be directly driven by the LOS (loss of signal) detector output (SDOUT). If the squelch function is not required, the pin should be tied to VEE. TEST MODES: BYPASS AND LOOPBACK When the bypass input is driven to a TTL high state, the quantizer output is connected directly to the buffers driving the data out pins, thus bypassing the clock recovery circuit (see Figure 21). This feature can help the system deal with nonstandard bit rates. The loopback mode can be invoked by driving the LOOPEN pin to a TTL high state, which facilitates system diagnostic testing. This connects the test inputs (TDINP/N) to the clock and data recovery circuit (per Figure 21). The test inputs have internal 50 Ω terminations, and can be left floating when not in use. TDINP/N are CML inputs and can only be dc-coupled when being driven by CML outputs. The TDINP/N inputs must be ac-coupled if driven by anything other than CML outputs. Bypass and loopback modes are mutually exclusive: only one of these modes can be used at any given time. The ADN2819 is put into an indeterminate state if both the BYPASS and LOOPEN pins are set to Logic 1 at the same time. Rev. B | Page 16 of 24 ADN2819 APPLICATIONS INFORMATION PCB DESIGN GUIDELINES The high speed inputs, PIN and NIN, are internally terminated with 50 Ω to an internal reference voltage (see Figure 24). A 0.1 µF capacitor is recommended between VREF, Pin 4, and GND to provide an ac ground for the inputs. Proper RF PCB design techniques must be used for optimal performance. Power Supply Connections and Ground Planes Use of one low impedance ground plane to both analog and digital grounds is recommended. The VEE pins should be soldered directly to the ground plane to reduce series inductance. If the ground plane is an internal plane and connections to the ground plane are made through vias, multiple vias may be used in parallel to reduce the series inductance, especially on Pins 33 and 34, which are the ground returns for the output buffers. Use of a 10 µF electrolytic capacitor between VCC and GND is recommended at the location where the 3.3 V supply enters the PCB. Use of 0.1 µF and 1 nF ceramic chip capacitors should be placed between IC power supply VCC and GND as close as possible to the ADN2819 VCC pins. Again, if connections to the supply and ground are made through vias, the use of multiple vias in parallel will help to reduce series inductance, especially on Pins 35 and 36, which supply power to the high speed CLKOUTP/N and DATAOUTP/N output buffers. Refer to the schematic in Figure 22 for recommended connections. As with any high speed mixed-signal design, take care to keep all high speed digital traces away from sensitive analog nodes. Soldering Guidelines for Chip Scale Package The lands on the 48-lead LFCSP are rectangular. The printed circuit board 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 printed circuit board should be at least as large as this exposed pad. The user must connect the exposed pad to analog VCC. If vias are used, they should be incorporated into the pad at 1.2 mm pitch grid. The via diameter should be between 0.3 mm and 0.33 mm; the via barrel should be plated with 1 oz. copper to plug the via. Transmission Lines Use of 50 Ω transmission lines are required for all high frequency input and output signals to minimize reflections, including PIN, NIN, CLKOUTP, CLKOUTN, DATAOUTP, and DATAOUTN (also REFCLKP/N for a 155.52 MHz REFCLK). It is also recommended that the PIN/NIN input traces are matched in length and that the CLKOUTP/N and DATAOUTP/N traces are matched in length. All high speed CML outputs, CLKOUTP/N and DATAOUTP/N, also require 100 Ω back termination chip resistors connected between the output pin and VCC. These resistors should be placed as close as possible to the output pins. These 100 Ω resistors are in parallel with on-chip 100 Ω termination resistors to create a 50 Ω back termination (see Figure 23). Rev. B | Page 17 of 24 ADN2819 VCC 50Ω TRANSMISSION LINES 4 × 100Ω CLKOUTP VCC CLKOUTN µC DATAOUTP 10µF 1nF DATAOUTN DATAOUTP SQUELCH CLKOUTN CLKOUTP VEE VEE BYPASS SDOUT VCC VEE DATAOUTN LOOPEN 0.1µF 48 47 46 45 44 43 42 41 40 39 38 37 RTH THRADJ VCC VCC 1nF 0.1µF 0.1µF VEE VREF 50Ω PIN TIA NIN 50Ω SLICEP CIN VCC SLICEN VEE LOL µC XO1 19.44MHz XO2 1 36 2 35 3 34 4 33 EXPOSED PAD TIED OFF TO VCC PLANE WITH VIAS 5 6 32 31 7 30 8 29 28 9 0.1µF 1nF 10 11 27 26 ADN2819 25 12 VCC VCC VCC 0.1µF 1nF VEE VEE SEL0 SEL1 µC SEL2 VEE VCC 0.1µF 1nF VEE VCC VCC CF2 4.7µF (SEE TABLE 8 FOR SPECS) µC REFSEL0 µC REFSEL1 VEE CF1 VCC VEE NC TDINN TDINP NC VEE REFSEL REFCLKP VCC NC REFCLKN 13 14 15 16 17 18 19 20 21 22 23 24 02999-B-022 VCC 0.1µF 1nF Figure 22. Typical Application Circuit VCC VCC VCC ADN2819 VTERM 100Ω 100Ω 100Ω 100Ω 0.1µ F 0.1µ F 50Ω CIN 50Ω CIN 50Ω TIA NIN 50Ω 50Ω 0.1µ F 50Ω VREF 02999-B-024 VTERM 02999-B-023 50Ω ADN2819 PIN 50Ω Figure 23. AC-Coupled Output Configuration Figure 24. AC-Coupled Input Configuration Rev. B | Page 18 of 24 ADN2819 CHOOSING AC-COUPLING CAPACITORS The choice of ac-coupling capacitors at the input (PIN, NIN) and output (DATAOUTP, DATAOUTN) of the ADN2819 must be chosen such that the device works properly at the lower OC-3 and higher OC-48 data rates. 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 drop due to baseline wander (see Figure 23), causing pattern dependent jitter (PDJ). V1 ADN2819 CIN V2 PIN TIA CIN V2b COUT + 50Ω VREF V1b For the ADN2819 to work robustly at both OC-3 and OC-48, a minimum capacitor of 1.6 µF to PIN/NIN and 0.1 µF on DATAOUTP/DATAOUTN should be used. This is based on the assumption that 1000 CIDs must be tolerated and that the PDJ should be limited to 0.01 UI p-p. DATAOUTP LIMAMP CDR COUT 50Ω DATAOUTN NIN 1 2 3 4 V1 V1b V2 VREF V2b VTH VDIFF NOTES 1. DURING DATA PATTERNS WITH HIGH TRANSITION DENSITY, DIFFERENTIAL DC VOLTAGE AT V1 AND V2 IS 0. 2. WHEN THE OUTPUT OF THE TIA GOES TO CID, V1 AND V1b ARE DRIVEN TO DIFFERENT DC LEVELS. V2 AND V2b DISCHARGE TO THE VREF LEVEL, WHICH EFFECTIVELY INTRODUCES A DIFFERENTIAL DC OFFSET ACROSS THE AC COUPLING CAPACITORS. 3. WHEN THE BURST OF DATA STARTS AGAIN,THE DIFFERENTIAL DC OFFSET ACROSS THE AC COUPLING CAPACITORS IS APPLIED TO THE INPUT LEVELS, CAUSING A DC SHIFT IN THE DIFFERENTIAL INPUT. THIS SHIFT IS LARGE ENOUGH SUCH THAT ONE OF THE STATES, EITHER HIGH OR LOW DEPENDING ON THE LEVELS OF V1 AND V1b WHEN THE TIA WENT TO CID, IS CANCELLED OUT. THE QUANTIZER WILL NOT RECOGNIZE THIS AS A VALID STATE. 4. THE DC OFFSET SLOWLY DISCHARGES UNTIL THE DIFFERENTIAL INPUT VOLTAGE EXCEEDS THE SENSITIVITY OF THE ADN2819. THE QUANTIZER WILL BE ABLE TO RECOGNIZE BOTH HIGH AND LOW STATES AT THIS POINT. Figure 25. Example of Baseline Wander Rev. B | Page 19 of 24 02999-B-025 VDIFF = V2–V2b VTH = ADN2819 QUANTIZER THRESHOLD ADN2819 DC-COUPLED APPLICATION VCC The inputs to the ADN2819 can also be dc-coupled. This may be necessary in burst mode applications where there are long periods of CIDs and baseline wander cannot be tolerated. If the inputs to the ADN2819 are dc-coupled, care must be taken not to violate the input range and common-mode level requirements of the ADN2819 (see Figure 26, Figure 27, and Figure 28). If dc-coupling is required, and the output levels of the TIA do not adhere to the levels shown in Figure 27 and Figure 28, there needs to be level shifting and/or an attenuator between the TIA outputs and the ADN2819 inputs. LOL TOGGLING DURING LOSS OF INPUT DATA 50Ω TIA • 50Ω PIN NIN 50Ω 50Ω VREF 02999-B-026 0.1µ F Figure 26. ADN2819 with DC-Coupled Inputs INPUT (V) If the input data stream is lost due to a break in the optical link (or for any reason), the clock output from the ADN2819 will stay within 1000 ppm of the VCO center frequency as long as there is a valid reference clock. The LOL pin toggles at a rate of several kHz because the LOL pin toggles between a Logic 1 and a Logic 0, while the frequency loop and phase loop swap control of the VCO. The chain of events is as follows: • ADN2819 V p-p = PIN – NIN = 2 × VSE = 10mV AT SENSITIVITY PIN VCM = 0.4V MIN (DC-COUPLED) 02999-B-027 NIN The ADN2819 is locked to the input data stream; LOL = 0. The input data stream is lost due to a break in the link. The VCO frequency drifts until the frequency error is greater than 1000 ppm. LOL is asserted to a Logic 1 as control of the VCO is passed back to the frequency loop. VSE = 5mV MIN Figure 27. Minimum Allowed DC-Coupled Input Levels INPUT (V) V p-p = PIN – NIN = 2 × VSE = 2.4V MAX PIN VSE = 1.2V MAX The frequency loop pulls the VCO to within 500 ppm of its center frequency. Control of the VCO is passed back to the phase loop and LOL is deasserted to a Logic 0. • The phase loop tries to acquire, but there is no input data present so the VCO frequency drifts. • The VCO frequency drifts until the frequency error is greater than 1000 ppm. LOL is asserted to a Logic 1 as control of the VCO is passed back to the frequency loop. This process is repeated until a valid input data stream is re-established. Rev. B | Page 20 of 24 VCM = 0.6V (DC-COUPLED) NIN Figure 28. Maximum Allowed DC-Coupled Input Levels 02999-B-028 • ADN2819 OUTLINE DIMENSIONS 7.00 BSC SQ 0.60 MAX 0.60 MAX 37 36 PIN 1 INDICATOR TOP VIEW 12° MAX PIN 1 INDICATOR 48 1 EXPOSED PAD 6.75 BSC SQ 5.25 5.10 SQ 4.95 (BOTTOM VIEW) 0.50 0.40 0.30 1.00 0.85 0.80 0.30 0.23 0.18 25 24 12 13 0.25 MIN 5.50 REF 0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM 0.50 BSC SEATING PLANE 0.20 REF COPLANARITY 0.08 COMPLIANT TO JEDEC STANDARDS MO-220-VKKD-2 Figure 29. 48-Lead Lead Frame Chip Scale Package [LFCSP] 7 mm × 7 mm Body (CP-48) Dimensions shown in millimeters ORDERING GUIDE Model ADN2819ACP-CML ADN2819ACP-CML-RL ADN2819ACPZ-CML1 ADN2819ACPZ-CML-RL1 EVAL-ADN2819-CML 1 Temperature Range –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C Package Description 48-Lead LFCSP 48-Lead LFCSP 48-Lead LFCSP 48-Lead LFCSP Evaluation Board Z = Pb Free. Rev. B | Page 21 of 24 Package Option CP-48 CP-48 CP-48 CP-48 ADN2819 NOTES Rev. B | Page 22 of 24 ADN2819 NOTES Rev. B | Page 23 of 24 ADN2819 NOTES © 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C02999–0–5/04(B) Rev. B | Page 24 of 24