ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER GENERAL DESCRIPTION FEATURES The ICS8421002I is a 2 output HSTL Synthesizer optimized to generate Fibre Channel reference HiPerClockS™ clock frequencies and is a member of the HiPerClocksTM family of high performance clock solutions from ICS. Using a 26.5625MHz 18pF parallel resonant crystal, the following frequencies can be generated based on the 2 frequency select pins (F_SEL[1:0]): 212.5MHz, 187.5MHz, 159.375MHz, 106.25MHz and 53.125MHz. The ICS8421002I uses ICS’ 3rd generation low phase noise VCO technology and can achieve 1ps or lower typical rms phase jitter, easily meeting Fibre Channel jitter requirements. The ICS8421002I is packaged in a small 20-pin TSSOP package. • Two HSTL outputs (VOHmax = 1.5V) ICS • Selectable crystal oscillator interface or LVCMOS/LVTTL single-ended input • Supports the following output frequencies: 212.5MHz, 187.5MHz, 159.375MHz, 106.25MHz, 53.125MHz • VCO range: 560MHz - 680MHz • RMS phase jitter @ 212.5MHz, using a 26.5625MHz crystal (637kHz - 10MHz): 0.59ps (typical) • Power supply modes: Core/Output 3.3V/1.8V 2.5V/1.8V • -40°C to 85°C ambient operating temperature • Available in both standard an lead-free RoHS compliant packages PIN ASSIGNMENT FREQUENCY SELECT FUNCTION TABLE Input Frequency (MHz) Inputs M Divider N Divider Value Value 24 3 F_SEL1 F_SEL0 26.5625 0 0 26.5625 0 1 24 26.5625 1 0 26.5625 1 1 23.4375 0 0 M/N Divider Value 8 Output Frequency (MHz) 212.5 4 6 159.375 24 6 4 106.25 24 12 2 53.125 24 3 8 187.5 nPLL_SEL nQ0 MR nPLL_SEL nc VDDA F_SEL0 VDD 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 VDDO Q1 nQ1 GND VDD nXTAL_SEL REF_CLK XTAL_IN XTAL_OUT F_SEL1 ICS8421002I 20-Lead TSSOP 6.5mm x 4.4mm x 0.92mm package body G Package Top View BLOCK DIAGRAM 2 F_SEL[1:0] Pulldown nc VDDO Q0 Pulldown Q0 REF_CLK Pulldown F_SEL[1:0] 0 0 ÷3 (default) 1 1 26.5625MHz XTAL_IN OSC 0 Phase Detector VCO 0 01 ÷4 10 11 ÷6 ÷12 nQ0 Q1 nQ1 XTAL_OUT nXTAL_SEL Pulldown M = 24 (fixed) MR Pulldown The Preliminary Information presented herein represents a product in prototyping or pre-production. The noted characteristics are based on initial product characterization. Integrated Circuit Systems, Incorporated (ICS) reserves the right to change any circuitry or specifications without notice. 8421002AGI www.icst.com/products/hiperclocks.html REV. A FEBRUARY 7, 2006 1 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER TABLE 1. PIN DESCRIPTIONS Number Name 1, 7 nc Unused 2, 20 VDDO Power 3, 4 Q0, nQ0 Ouput 5 MR Input 6 nPLL_SEL Input 8 Power Input Pulldown Frequency select pins. LVCMOS/LVTTL interface levels. Power 14 VDDA F_SEL0, F_SEL1 VDD XTAL_OUT, XTAL_IN REF_CLK Differential output pair. HSTL interface levels. Active HIGH Master Reset. When logic HIGH, the internal dividers are reset causing the true outputs Qx to go low and the inver ted outputs nQx Pulldown to go high. When logic LOW, the internal dividers and the outputs are enabled. LVCMOS/LVTTL interface levels. Selects between the PLL and REF_CLK as input to the dividers. When Pulldown LOW, selects PLL (PLL Enable). When HIGH, deselects the reference clock (PLL Bypass). LVCMOS/LVTTL interface levels. Analog supply pin. 15 nXTAL_SEL Input Core supply pin. Parallel resonant cr ystal interface. XTAL_OUT is the output, XTAL_IN is the input. Pulldown LVCMOS/LVTTL reference clock input. Selects between cr ystal or REF_CLK inputs as the the PLL Reference Pulldown source. Selects XTAL inputs when LOW. Selects REF_CLK when HIGH. LVCMOS/LVTTL interface levels. Power supply ground. 9, 11 10, 16 12, 13 Type Input Input 17 GND Power 18, 19 nQ1, Q1 Output Description No connect. Output supply pins. Differential output pair. HSTL interface levels. NOTE: Pulldown refers to internal input resistors. See Table 2, Pin Characteristics, for typical values. TABLE 2. PIN CHARACTERISTICS Symbol Parameter CIN Input Capacitance 4 pF RPULLDOWN Input Pulldown Resistor 51 kΩ 8421002AGI Test Conditions Minimum www.icst.com/products/hiperclocks.html 2 Typical Maximum Units REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER ABSOLUTE MAXIMUM RATINGS Supply Voltage, VDD 4.6V Inputs, VI -0.5V to VDD + 0.5V Outputs, IO Continuous Current Surge Current 50mA 100mA Package Thermal Impedance, θJA 73.2°C/W (0 lfpm) Storage Temperature, TSTG -65°C to 150°C NOTE: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These ratings are stress specifications only. Functional operation of product at these conditions or any conditions beyond those listed in the DC Characteristics or AC Characteristics is not implied. Exposure to absolute maximum rating conditions for extended periods may affect product reliability. TABLE 3A. POWER SUPPLY DC CHARACTERISTICS, VDD = VDDA = 3.3V±5%, VDDO = 1.8V±0.2V, TA = -40°C TO 85°C Symbol Parameter Minimum Typical Maximum Units VDD Core Supply Voltage Test Conditions 3.135 3.3 3.465 V VDDA Analog Supply Voltage 3.135 3.3 3.465 V 3.135 3.3 VDDO Output Supply Voltage 3.465 V IDD Power Supply Current 110 mA IDDA Analog Supply Current 12 mA IDDO Output Supply Current No Load 0 mA TABLE 3B. POWER SUPPLY DC CHARACTERISTICS, VDD = VDDA = 2.5V±5%, VDDO = 1.8V±0.2V, TA = -40°C TO 85°C Symbol Parameter Minimum Typical Maximum Units VDD Core Supply Voltage Test Conditions 2.375 2.5 2.625 V VDDA Analog Supply Voltage 2.375 2.5 2.625 V VDDO Output Supply Voltage 2.375 2.5 2.625 V IDD Power Supply Current 96 mA 12 mA IDDA Analog Supply Current IDDO Output Supply Current No Load 0 mA TABLE 3C. LVCMOS / LVTTL DC CHARACTERISTICS, VDD = VDDA = 3.3V±5% OR 2.5V±5%, VDDO = 1.8V±0.2V, TA = -40°C TO 85°C Symbol Parameter VIH Input High Voltage VIL Input Low Voltage IIH Input High Current IIL Input Low Current 8421002AGI Test Conditions VDD = 3.3V REF_CLK, MR, F_SEL0, F_SEL1, nPLL_SEL, nXTAL_SEL REF_CLK, MR, F_SEL0, F_SEL1, nPLL_SEL, nXTAL_SEL Minimum Typical 2 Maximum VDD + 0.3 Units V VDD = 2.5V 1.7 VDD + 0.3 V VDD = 3.3V -0.3 0.8 V VDD = 2.5V -0.3 0.7 V 150 µA VDD = VIN = 3.465V or 2.5V VDD = 3.465V or 2.5V, VIN = 0V www.icst.com/products/hiperclocks.html 3 -150 µA REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER TABLE 3D. HSTL DC CHARACTERISTICS, VDD = VDDA = 3.3V±5%, VDDO = 1.8V±0.2V, TA = -40°C TO 85°C Symbol Parameter Maximum Units VOH Output High Voltage; NOTE 1 Test Conditions Minimum 1.0 1.5 V VOL Output Low Voltage; NOTE 1 0 0.5 V VOX Output Crossover Voltage; NOTE 2 40 60 % 0.6 1.3 V Peak-to-Peak Output Voltage Swing VSWING NOTE 1: Outputs terminated with 50Ω to ground. NOTE 2: Defined with respect to output voltage swing at a given condition. Typical TABLE 3E. HSTL DC CHARACTERISTICS, VDD = VDDA = 2.5V±5%, VDDO = 1.8V±0.2V, TA = -40°C TO 85°C Symbol Parameter Maximum Units VOH Output High Voltage; NOTE 1 Test Conditions Minimum 0.8 1.5 V VOL Output Low Voltage; NOTE 1 0 0.6 V VOX Output Crossover Voltage; NOTE 2 40 60 % 0.5 1.5 V Maximum Units Peak-to-Peak Output Voltage Swing VSWING NOTE 1: Outputs terminated with 50Ω to ground. NOTE 2: Defined with respect to output voltage swing at a given condition. Typical TABLE 4. CRYSTAL CHARACTERISTICS Parameter Test Conditions Minimum Mode of Oscillation Typical Fundamental 28.33 MHz Equivalent Series Resistance (ESR) Frequency 23.33 26.5625 50 Ω Shunt Capacitance 7 pF Drive Level 1 mW NOTE: Characterized using an 18pF parallel resonant crystal. 8421002AGI www.icst.com/products/hiperclocks.html 4 REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER TABLE 5A. AC CHARACTERISTICS, VDD = VDDA = 3.3V±5%, VDDO = 1.8V±0.2V, TA = -40°C TO 85°C Symbol Parameter fOUT Output Frequency tsk(o) Output Skew; NOTE 1, 3 tjit(Ø) t R / tF RMS Phase Jitter (Random); NOTE 2 Output Rise/Fall Time Test Conditions Minimum F_SEL[1:0] = 00 186.67 Typical Maximum Units 226.66 MHz F_SEL[1:0] = 01 140 170 MHz F_SEL[1:0] = 10 93.33 113.33 MH z F_SEL[1:0] = 11 46.67 56.66 MHz 20 ps 212.5MHz, (637kHz - 10MHz) 0.59 ps 187.5MHz, (1.875MHz - 20MHz) 0.51 ps 159.375MHz, (637kHz - 10MHz) 0.56 ps 106.25MHz, (637kHz - 10MHz) 0.69 ps 53.125MHz, (637kHz - 10MHz) 0.66 ps 20% to 80% 175 N Divider = 4, 6, 12 48 odc Output Duty Cycle N Divider = 3 44 NOTE 1: Defined as skew between outputs at the same supply voltages and with equal load conditions. Measured at VDDO/2. NOTE 2: Please refer to the Phase Noise Plot. NOTE 3: This parameter is defined in accordance with JEDEC Standard 65. 875 ps 52 56 % % Maximum Units 226.66 MHz TABLE 5B. AC CHARACTERISTICS, VDD = VDDA = 2.5V±5%, VDDO = 1.8V±0.2V, TA = -40°C TO 85°C Symbol Parameter fOUT Output Frequency t sk(o) Output Skew; NOTE 1, 3 t jit(Ø) tR / tF RMS Phase Jitter (Random); NOTE 2 Output Rise/Fall Time Test Conditions Minimum F_SEL[1:0] = 00 186.67 Typical F_SEL[1:0] = 01 140 170 MHz F_SEL[1:0] = 10 93.33 113.33 MHz F_SEL[1:0] = 11 46.67 56.66 MHz 20 ps 212.5MHz, (637kHz - 10MHz) 0.60 ps 187.5MHz, (1.875MHz - 20MHz) 0.70 ps 159.375MHz, (637kHz - 10MHz) 0.64 ps 106.25MHz, (637kHz - 10MHz) 0.70 ps 53.125MHz, (637kHz - 10MHz) 0.68 ps 20% to 80% 200 N Divider = 4, 6, 12 48 odc Output Duty Cycle N Divider = 3 44 NOTE 1: Defined as skew between outputs at the same supply voltages and with equal load conditions. Measured at VDDO/2. NOTE 2: Please refer to the Phase Noise Plot. NOTE 3: This parameter is defined in accordance with JEDEC Standard 65. 8421002AGI www.icst.com/products/hiperclocks.html 5 700 ps 52 56 % % REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER TYPICAL PHASE NOISE 0 AT 212.5MHZ @ 3.3V ➤ -10 -20 Fibre Channel Jitter Filter -30 -40 -50 212.5MHz RMS Phase Jitter (Random) 637kHz to 10MHz = 0.59ps (typical) -70 -80 -90 Raw Phase Noise Data -100 -110 ➤ NOISE POWER dBc Hz -60 -120 -130 -140 ➤ -150 -160 -170 -180 Phase Noise Result by adding Fibre Channel Filter to raw data -190 100 1k 10k 100k 1M 10M 100M OFFSET FREQUENCY (HZ) TYPICAL PHASE NOISE 0 AT 53.125MHZ @ 3.3V ➤ -10 -20 Fibre Channel Jitter Filter -30 -50 53.125MHz -60 RMS Phase Jitter (Random) 637kHz to 10MHz = 0.66ps (typical) -70 -80 -90 -100 Raw Phase Noise Data -110 -120 ➤ NOISE POWER dBc Hz -40 -130 -140 -150 ➤ -160 -170 -180 Phase Noise Result by adding Fibre Channel Filter to raw data -190 100 1k 10k 100k 1M 10M 100M OFFSET FREQUENCY (HZ) 8421002AGI www.icst.com/products/hiperclocks.html 6 REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER PARAMETER MEASUREMENT INFORMATION VDD VDD VDDA VDDA VDDO VDDO Qx SCOPE Qx SCOPE HSTL HSTL GND GND nQx nQx 0V 0V HSTL 3.3V/1.8V OUTPUT LOAD AC TEST CIRCUIT HSTL 2.5V/1.8V OUTPUT LOAD AC TEST CIRCUIT nQx 80% 80% Qx VSW I N G Clock Outputs nQy 20% 20% Qy tF tR tsk(o) OUTPUT SKEW OUTPUT RISE/FALL TIME Phase Noise Plot nQ0, nQ1 Noise Power Q0, Q1 Pulse Width t Phase Noise Mask odc = f1 Offset Frequency PERIOD t PW t PERIOD f2 RMS Jitter = Area Under the Masked Phase Noise Plot RMS PHASE JITTER 8421002AGI OUTPUT DUTY CYCLE/PULSE WIDTH/PERIOD www.icst.com/products/hiperclocks.html 7 REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER APPLICATION INFORMATION POWER SUPPLY FILTERING TECHNIQUES As in any high speed analog circuitry, the power supply pins are vulnerable to random noise. The ICS8421002I provides separate power supplies to isolate any high switching noise from the outputs to the internal PLL. VDD, VDDA, and VDDO should be individually connected to the power supply plane through vias, and bypass capacitors should be used for each pin. To achieve optimum jitter performance, power supply isolation is required. Figure 1 illustrates how a 10Ω resistor along with a 10µF and a .01μF bypass capacitor should be connected to each VDDA. 3.3V or 2.5V VDD .01μF 10Ω VDDA .01μF 10μF FIGURE 1. POWER SUPPLY FILTERING CRYSTAL INPUT INTERFACE below were determined using a 26.5625MHz 18pF parallel resonant crystal and were chosen to minimize the ppm error. The ICS8421002I has been characterized with 18pF parallel resonant crystals. The capacitor values shown in Figure 2 XTAL_OUT C1 22p X1 18pF Parallel Crystal XTAL_IN C2 22p ICS8421002I Figure 2. CRYSTAL INPUt INTERFACE RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS INPUTS: OUTPUTS: CRYSTAL INPUT: For applications not requiring the use of the crystal oscillator input, both XTAL_IN and XTAL_OUT can be left floating. Though not required, but for additional protection, a 1kΩ resistor can be tied from XTAL_IN to ground. HSTL OUTPUT All unused HSTL outputs can be left floating. We recommend that there is no trace attached. Both sides of the differential output pair should either be left floating or terminated. REF_CLK INPUT: For applications not requiring the use of the reference clock, it can be left floating. Though not required, but for additional protection, a 1kΩ resistor can be tied from the REF_CLK to ground. LVCMOS CONTROL PINS: All control pins have internal pull-ups or pull-downs; additional resistance is not required but can be added for additional protection. A 1kΩ resistor can be used. 8421002AGI www.icst.com/products/hiperclocks.html 8 REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER POWER CONSIDERATIONS This section provides information on power dissipation and junction temperature for the ICS8421002I. Equations and example calculations are also provided. 1. Power Dissipation. The total power dissipation for the ICS8421002I is the sum of the core power plus the power dissipated in the load(s). The following is the power dissipation for VDD = 3.3V + 5% = 3.465V, which gives worst case results. NOTE: Please refer to Section 3 for details on calculating power dissipated in the load. • • Power (core)MAX = VDD_MAX * IDD_MAX = 3.465V * 122mA = 422.7mW Power (outputs)MAX = 32.8mW/Loaded Output pair If all outputs are loaded, the total power is 2 * 32.8mW = 65.6mW Total Power_MAX (3.465V, with all outputs switching) = 422.7mW + 65.6mW = 488.3mW 2. Junction Temperature. Junction temperature, Tj, is the temperature at the junction of the bond wire and bond pad and directly affects the reliability of the device. The maximum recommended junction temperature for HiPerClockSTM devices is 125°C. The equation for Tj is as follows: Tj = θJA * Pd_total + TA Tj = Junction Temperature θJA = Junction-to-Ambient Thermal Resistance Pd_total = Total Device Power Dissipation (example calculation is in section 1 above) TA = Ambient Temperature In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance θJA must be used. Assuming a moderate air flow of 200 linear feet per minute and a multi-layer board, the appropriate value is 66.6°C/W per Table 6 below. Therefore, Tj for an ambient temperature of 85°C with all outputs switching is: 85°C + 0.488W * 66.6°C/W = 117.5°C. This is below the limit of 125°C. This calculation is only an example. Tj will obviously vary depending on the number of loaded outputs, supply voltage, air flow, and the type of board (single layer or multi-layer). TABLE 6. THERMAL RESISTANCE θJA FOR 20-PIN TSSOP, FORCED CONVECTION θJA by Velocity (Linear Feet per Minute) Single-Layer PCB, JEDEC Standard Test Boards Multi-Layer PCB, JEDEC Standard Test Boards 0 200 500 114.5°C/W 73.2°C/W 98.0°C/W 66.6°C/W 88.0°C/W 63.5°C/W NOTE: Most modern PCB designs use multi-layered boards. The data in the second row pertains to most designs. 8421002AGI www.icst.com/products/hiperclocks.html 9 REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER 3. Calculations and Equations. The purpose of this section is to derive the power dissipated into the load. HSTL output driver circuit and termination are shown in Figure 3. VDDO Q1 VOUT RL 50Ω FIGURE 3. HSTL DRIVER CIRCUIT AND TERMINATION To calculate worst case power dissipation into the load, use the following equations which assume a 50Ω load. Pd_H is power dissipation when the output drives high. Pd_L is the power dissipation when the output drives low. Pd_H = (V /R ) * (V OH_MAX Pd_L = (V OL_MAX L -V DD_MAX /R ) * (V L DD_MAX ) OH_MAX -V ) OL_MAX Pd_H = (1V/50Ω) * (2V - 1V) = 20mW Pd_L = (0.4V/50Ω) * (2V - 0.4V) = 12.8mW Total Power Dissipation per output pair = Pd_H + Pd_L = 32.8mW 8421002AGI www.icst.com/products/hiperclocks.html 10 REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER RELIABILITY INFORMATION TABLE 7. θJAVS. AIR FLOW TABLE FOR 20 LEAD TSSOP θJA by Velocity (Meters per Second) Single-Layer PCB, JEDEC Standard Test Boards Multi-Layer PCB, JEDEC Standard Test Boards 0 200 500 114.5°C/W 73.2°C/W 98.0°C/W 66.6°C/W 88.0°C/W 63.5°C/W NOTE: Most modern PCB designs use multi-layered boards. The data in the second row pertains to most designs. TRANSISTOR COUNT The transistor count for ICS8421002I is: 2951 8421002AGI www.icst.com/products/hiperclocks.html 11 REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. PACKAGE OUTLINE - G SUFFIX FOR FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER 20 LEAD TSSOP TABLE 8. PACKAGE DIMENSIONS Millimeters SYMBOL MIN N MAX 20 A -- 1.20 A1 0.05 0.15 A2 0.80 1.05 b 0.19 0.30 c 0.09 0.20 D 6.40 E E1 6.60 6.40 BASIC 4.30 e 4.50 0.65 BASIC L 0.45 0.75 α 0° 8° aaa -- 0.10 Reference Document: JEDEC Publication 95, MO-153 8421002AGI www.icst.com/products/hiperclocks.html 12 REV. A FEBRUARY 7, 2006 ICS8421002I Integrated Circuit Systems, Inc. FEMTOCLOCKS™ CRYSTAL-TOHSTL FREQUENCY SYNTHESIZER TABLE 9. ORDERING INFORMATION Part/Order Number Marking Package Shipping Packaging Temperature ICS8421002AGI ICS8421002AI 20 Lead TSSOP tube -40°C to 85°C ICS8421002AGIT ICS8421002AI 20 Lead TSSOP 2500 tape & reel -40°C to 85°C ICS8421002AGILF ICS421002AIL 20 Lead "Lead-Free" TSSOP tube -40°C to 85°C ICS8421002AGILFT ICS421002AIL 20 Lead "Lead-Free" TSSOP 2500 tape & reel -40°C to 85°C NOTE: Par ts that are ordered with an "LF" suffix to the par t number are the Pb-Free Configuration and are RoHS compliant. The aforementioned trademarks, HiPerClockS and FEMTOCLOCKS are trademarks of Integrated Circuit Systems, Inc. or its subsidiaries in the United States and/or other countries. While the information presented herein has been checked for both accuracy and reliability, Integrated Circuit Systems, Incorporated (ICS) assumes no responsibility for either its use or for infringement of any patents or other rights of third parties, which would result from its use. No other circuits, patents, or licenses are implied. This product is intended for use in normal commercial and industrial applications. Any other applications such as those requiring high reliability or other extraordinary environmental requirements are not recommended without additional processing by ICS. ICS reserves the right to change any circuitry or specifications without notice. ICS does not authorize or warrant any ICS product for use in life support devices or critical medical instruments. 8421002AGI www.icst.com/products/hiperclocks.html 13 REV. A FEBRUARY 7, 2006