CS61600 Semiconductor Corporation PCM Jitter Attenuator Features General Description • The CS61600 from Crystal Semiconductor accepts T1 (1.544 Mb/s) or CCITT standard (2.048 Mb/s) data and clock inputs, and tolerates at least 7 (and up to 14) unit intervals, peak-to-peak, of jitter. Before outputting data and clock, jitter is attenuated using an internal clocktracking variable oscillator and a 16 bit FIFO elastic store. Unique Clock-Tracking Circuitry Filters 50 Hz or Higher Frequency Jitter for T1 and PCM-30 Applications • Minimal External Components Required • 14 Pin DIP • Single 5 Volt Supply • 3 Micron CMOS for High Reliability The jitter attenuation function can be determined by appropriate specification of the external crystal. The CS61600 is transparent to data format, and is intended for application in carrier systems, switching systems, Local Area Network gateways and multiplexers. and Low Power Dissipation: 50 mW Typical at 25 °C FIFORST ORDERING INFORMATION CS61600-IP1 - 14 Pin Plastic DIP; T1 and 2.048 MHz OVR 2 RESET 3 1 FIFO CONTROL DIN CLKIN 13 9 16-BIT FIFO 8 10 6 HALF FULL DETECT 12 14 VARIABLE OSCILLATOR Crystal Semiconductor Corporation P.O. Box 17847, Austin, TX 78760 (512) 445-7222 FAX: (512) 445-7581 4 5 XTALIN XTALOUT ÷4 7 DOUT CLKOUT ARE ARC V+ GND 11 OSCOUT Copyright Crystal Semicondutor Corporation 1994 (All Rights Reserved) APR ’90 DS9F3 1 CS61600 ABSOLUTE MAXIMUM RATINGS Parameter Symbol Min Max Units (V+)-GND -0.3 7.0 V Vin GND - 0.3 (V+) + 0.3 V Iin -10 10 mA Ambient Operating Temperature TA -40 85 °C Storage Temperature Tstg -65 150 °C DC Supply Input Voltage Input Current, Any Pin Note: (Note 1) 1. Transient currents of up to 100 mA will not cause SCR latch-up. WARNING: Operation at or beyond these limits may result in permanent damage to the device. Normal operation is not guaranteed at these extremes. RECOMMENDED OPERATING CONDITIONS Parameter DC Supply Ambient Operating Temperature Symbol Min Typ Max Units (V+)-GND 4.5 5.0 5.5 V TA -40 25 85 °C DIGITAL CHARACTERISTICS (TA = -40° to 85° C; V+ = 5V ±10%; GND = 0V) Parameter Symbol Min Typ Max Units High-Level Input Voltage VIH 2.0 - - V Low-Level Input Voltage VIL - - 0.8 V High-Level Output Voltage (Notes 2 and 3) VOH 2.4 - - V Low-Level Output Voltage (Notes 2 and 4) VOL - - 0.4 V Iin - - ±10.0 µA Input Leakage Current Notes: 2. Outputs will drive CMOS logic levels into a CMOS load. 3. Iout = -40 µA 4. Iout = 1.6 mA Specifications subject to change without notice. 2 DS9F3 CS61600 DIGITAL CHARACTERISTICS (TA = -40° to 85° C; V+ = 5V ±10%; GND = 0V) Parameter Power Dissipation Symbol Min Typ Max Units PD - 50 85 mW 14* U.I. Input Jitter Tolerance 7 * Depends on accuracy of crystal with respect to CLKIN frequency. See Applications section. SWITCHING CHARACTERISTICS (TA = -40° to 85° C; V+ = 5V ±10%; GND = 0V; Inputs: Logic 0 = 0V, Logic 1 = V+) Parameter Crystal Frequency CLKIN Frequency CLKOUT Frequency Clock Pulse Width T1 CCITT (Note 5) T1 CCITT (Note 6) T1 CCITT (Note 6) T1 CCITT (Note 7) Symbol Min Typ Max Units fc - 6.176000 8.192000 - MHz fin - 1.544 2.048 - MHz fout - 1.544 2.048 - MHz tpwh tpwl - 324 324 - ns tpwh tpwl - 244 244 - ns Acceptable CLKIN range (Note 8) - ±130 - ppm Duty Cycle (Note 9) - 50 - % Rise Time, All Digital Outputs (Note 10) tr - 36 100 ns Fall Time, All Digital Outputs (Note 10) tf - 17 100 ns DIN to CLKIN Falling Setup Time tsu 30 - - ns CLKIN Falling to DIN Hold Time th 50 - - ns 200 ns CLKOUT Falling to DOUT Propogation Delay tphl Note: 5. Crystal should have sufficient pull range when in the oscillator circuit, to meet the system’s frequency tolerance requirement over the operating temperature range. See Applications section for more information on crystals. 6. Although CLKIN and CLKOUT will vary in instantaneous frequency (jitter) over time, CLKOUT will have the same average frequency as CLKIN. 7. The sum of the pulse widths must always meet the frequency specifications. 8. Crystal must have at least ±130ppm pull range over operating temperature range. 9. Duty cycle is (tPWH / (tPWH + tPWL)) x 100%. 10. At CL = 50pF. DS9F3 3 CS61600 tf tr Any Digital Output 90% 90% 10% 10% Figure 1. Signal Rise and Fall Characteristics t pwh t pwl CLKIN, CLKOUT Figure 2. Clock Signal Quality CLKIN CLKOUT t su DIN th t phl DOUT Figure 3. Switching Characteristics 4 DS9F3 CS61600 10.0 CS61600 PERFORMANCE 7.0 5.0 PEAK-TO-PEAK (SINUSOIDAL) JITTER AMPLITUDE IN UNIT INTERVALS 1.5 1.0 AT&T 43802 SPECIFICATION 0.2 0.1 20 10.0 500 100.0 2.4k 1.0k CCITT G.823 SPECIFICATION 8.0k 18k 10.0k JITTER FREQUENCY (Hz) Figure 4. Input Jitter Tolerance JITTER GAIN (dB) 0 20 dB/ decade -10 -20 BELL SYSTEM PUB 43802 SPECIFICATION CS61600 PERFORMANCE Input of five unit intervals of jitter at all frequencies. -30 -40 10 100 JITTER 1k FREQUENCY 10k (Hz) Figure 5. Jitter Attenuation Characteristic DS9F3 5 CS61600 CIRCUIT DESCRIPTION Jitter Attenuation The CS61600 will tolerate and attenuate at least seven unit intervals of jitter from clock and data signals of 1.544 MHz and 2.048 MHz. An external clock divide circuit can be added for jitter attenuation for lower frequency signals. Jitter attenuation is accomplished by means of a FIFO and a variable oscillator. The frequency of the oscillator is controlled by logic in the CS61600 to be the same as the average of the input clock signal, CLKIN. Signal jitter is absorbed in the FIFO. jitter attenuation, and the lower the frequency at which the device starts to attenuate jitter. Conversely, low amplitude jitter receives little attenuation. This performance characteristic is shown graphically in Figure 6. JITTER GAIN (dB) 0 5 3 1 ... -20 -30 -40 The FIFO’s write pointer is controlled by the CLKIN signal. Data present on DIN is written into the memory location selected by the write pointer. The CLKOUT signal corresponds to the FIFO’s read pointer and is controlled by the crystal oscillator. Internal logic determines the relationship of the read pointer and the write pointer, and adjusts the speed of the oscillator. For example, if the CLKIN signal is at a higher frequency than the CLKOUT signal, the write pointer will start to catch up with the read pointer. When this situation is detected, the capacitive loading the device presents to the crystal is reduced, resulting in an increase in oscillator frequency and read pointer (CLKOUT) frequency. The oscillator frequency is periodically updated and adjusted to maintain the FIFO at half full. High frequency variations in the phase of the CLKIN signal (jitter) are absorbed in the FIFO. UNIT INTERVALS OF INPUT JITTER -10 dB 10 Measurement made at 1.544 MHz with 6.176 MHz ±200 ppm crystal. 100 1k 10k (Hz) Figure 6. Jitter Attenuation Characteristics Using the CS61600 in a Slave Configuration It is possible to use an externally generated clock signal to clock data out of the CS61600. When an external clock is used, a crystal is not necessary. The external clock is input to the Alternate Read Clock input, ARC (pin 12). Holding the Alternate Read Enable pin, ARE (pin 6), high directs the CS61600 to clock data out of the FIFO at the rate determined by ARC. Unless the clock signal on ARC is at exactly the same average frequency as the clock signal on CLKIN, the CS61600 will be prone to underflow or overflow, and data will be lost. See the Applications section of this data sheet for more information on the use of an alternate clock. Oscillator and Crystal There are some advantages to this method of jitter attenuation. The device can tolerate large amplitude jitter at high frequencies. The device can track slow changes of the input clock frequency (wander) and tolerate input frequencies ranging over a specified frequency tolerance. A by product of this method of jitter attenuation is that the greater the input jitter, the greater the 6 The CS61600 requires an external 6.176000 MHz (8.192000 MHz for CCITT) crystal be connected to pins XTALOUT and XTALIN. The oscillator circuit divides the crystal frequency by four, and switches various capacitive loads to provide a clock that swings in five steps from at least 1.544 MHz - 130 ppm to at least 1.544 MHz + 130 ppm (2.048 MHz - 50 ppm to DS9F3 CS61600 2.048 MHz + 50 ppm for CCITT). The crystal oscillator must be able to reach these signal frequency tolerances over the system’s operating temperature range. The oscillator adjusts to and holds the average frequency of the signal input to CLKIN. Some applications specify a narrower frequency tolerance. In these cases, it is possible to improve jitter attenuation performance by specifying a crystal with less pull range. A narrow pull range crystal has the effect of shifting the curves shown in Figure 6 to the left. Care must be taken to ensure that the crystal/oscillator will reach the signal’s frequency extremes over the operating temperature range of the system. More information on specifying and testing crystals is provided in the Applications section at the back of this data sheet. FIFO Overflow/Underflow Because the oscillator clock, which is used to empty the FIFO, has a wider frequency range than the standard T1 input signal, the FIFO should never underflow or overflow. However, if underflow or overflow occurs, the buffer overflow/underflow flag, OVR (pin 3), goes high. A RESET (pin 1) resets the overflow flag. If an overflow occurs, the 16 bits of data in the FIFO are lost. An underflow condition causes the next 16 bits read from the FIFO to be invalid. In either case, the CS61600 will immediately attempt to relock on to the clock signal. Holding RESET low disables the overflow flag, OVR. eighth locations respectively. The oscillator will continue to run and CLKOUT will be held low. Power-Up Reset Upon power up, the CS61600 goes through an initialization procedure which requires approximately 3 ms. During this initialization procedure, OVR is held high. After initialization is complete, OVR goes low. When the clock signal is input to CLKIN, the CS61600 will immediately try to lock onto the clock signal on CLKIN. At this point, the FIFO may overflow, and the RESET pin should be toggled to clear the overflow/underflow flag, OVR. Schematic & Layout Review Service Confirm Optimum Schematic & Layout Before Building Your Board. For Our Free Review Service Call Applications Engineering. C a l l : ( 5 1 2 ) 4 4 5 - 7 2 2 2 FIFO Reset Taking the FIFORST pin low causes most of the subcircuits of the CS61600 to go into a reset state. These circuits will remain in a reset condition until FIFORST is returned to a logic 1 state. However, the outputs of the CS61600 are undefined if FIFORST is held low for more than 500 ms. The FIFO reset function will set the FIFO write and read pointers to the first and DS9F3 7 CS61600 PIN DESCRIPTIONS RESET FIFO RESET BUFFER OVERFLOW/UNDERFLOW CRYSTAL OUTPUT CRYSTAL INPUT ALTERNATE READ ENABLE GROUND RESET FIFORST OVR XTALIN XTALOUT ARE GND 1 14 2 13 3 12 4 11 5 6 10 9 7 8 V+ DIN ARC OSCOUT CLKOUT DOUT CLKIN POWER SUPPLY DATA INPUT ALTERNATE READ CLOCK OSCILLATOR OUTPUT OUTPUT CLOCK DATA OUTPUT INPUT CLOCK Power Supplies V+ - Positive Power Supply, PIN 14. Typically +5V volts. GND - Ground, PIN 7. Ground reference. Oscillator XTALIN, XTALOUT - Crystal Input 1, 2; PINS 4, 5. 6.176 MHz or 8.192 MHz crystal inputs. A 200 kohm resistor should be connected across these pins. There is no need for external capacitors. The crystal should be connected to XTALIN and XTALOUT with minimal length traces on the pc board. Control RESET - Reset, PIN 1. When RESET is taken low, the OVR signal is reset. FIFORST - FIFO Reset, PIN 2. Taking FIFORST low resets the read and write pointers of the FIFO. Resetting the pointers will cause some data loss. When FIFORST is low, the OSCOUT output is disabled. ARE - Alternate Read Enable, PIN 6. For normal operation, ARE is held at logic 0. In this configuration the oscillator controls the read pointer of the FIFO. When ARE is at logic 1, the read pointer of the FIFO will be controlled by the clock signal on pin 12, ARC. 8 DS9F3 CS61600 Inputs CLKIN - Clock Input, PIN 8. Clock for the data input. This clock contains the jitter to be removed. DIN - Data Input, PIN 13. Input data is sampled on the falling edge of CLKIN. ARC - Alternate Read Clock, PIN 12. When ARE, Pin 6, is at logic 1, a clock signal on ARC will control the FIFO’s read pointer. CLKOUT, pin 10, will be at the same frequency and phase as ARC. Setting ARE to logic 0 results in the device using its oscillator to generate CLKOUT. Outputs OVR - Buffer Overflow/Underflow, PIN 3. Goes high if the FIFO overflows or underflows, and is cleared by RESET. DOUT - Data Output, PIN 9. Output data with jitter attenuated. DOUT is stable and valid on the rising edge of CLKOUT. CLKOUT - Output Clock, PIN 10. Jitter reduced clock output corresponding to the data on DOUT. OSCOUT - Oscillator Output, Pin 11. Output of on-chip oscillator, divided by four. This pin should be left floating for normal operation. DS9F3 9 CS61600 RESET V+ +5V 10k V+ 10k 6.176 MHz 200k RESET 1 14 V+ FIFORST 2 13 DIN JITTERED DATA INPUT OVR 3 12 ARC XTALIN 4 11 OSCOUT XTALOUT 5 10 CLKOUT JITTER FREE CLOCK ARE 6 9 DOUT JITTER FREE DATA GND 7 8 CLKIN JITTERED CLOCK INPUT Figure A1. Typical Application Circuit APPLICATIONS the CLKIN signal approaches the fast end of its range, 1.544 MHz + 130 ppm. Selecting an Oscillator Crystal Specific crystal parameters are required for proper operation of the CS61600. It is recommend ed that the Crystal Semiconductor CXT6176 crystal be used for T1 applications and the CXT8192 crystal be used for PCM-30 applications. General Applications The CS61600 will tolerate and attenuate at least seven unit intervals of jitter over the specified range of input clock and oscillator frequencies. If the oscillator crystal is chosen so that the center frequency of its pull range is close to the input frequency, CLKIN, the CS61600 will tolerate more jitter; up to 14 unit intervals will be tolerated under optimal conditions. Consider the case where the average clock frequency at CLKIN approaches the slow end of the range, 1.544 MHz - 130 ppm. In this case, the oscillator will be near the bottom of its pull range, restricting its ability to achieve frequencies well below the CLKIN frequency. The result is that the read pointer of the FIFO will begin to catch up to the write pointer. If enough jitter is introduced, the read pointer will overtake the write pointer resulting in an error (i.e. the device will try to read out data before it is written in). A similar situation occurs when 10 Taking care in selecting the proper crystal can result in improved jitter tolerance without degrading the performance of the CS61600. If the center frequency of the oscillator is precisely four times the CLKIN frequency, and the crystal has at least the specified pull range, the CS61600 will tolerate 14 unit intervals of jitter. In this case, the read and write pointers of the FIFO will maintain optimal separation when the signal is jitter free, allowing the device to tolerate maximum jitter input. Master/Slave Configuration Some T1 applications require separate representations of the positive and negative going pulses for an AMI signal. Two CS61600s can be used to remove jitter from a set of signals consisting of POS, NEG and CLK. Figure A2 shows the master/slave configuration. This configuration requires one crystal (on the master). The CLKOUT signal from the master controls the FIFO read pointer of the slave CS61600. Setting ARE, pin 6, of the slave to logic 1 directs the device to use the clock input to ARC, pin 12, to control the FIFO read pointer. For this configuration to function properly, the positions of the FIFO read and write pointers in both devices must correspond. The FIFO pointer reset, FIFORST, of both devices must be tied toDS9F3 CS61600 V+ FIFO POINTER V+ CLKIN RESET 10k OVR RESET D R Q OVR RESET V+ SQ 10k V+ 10k OVR 200k 1 14 2 13 3 12 4 11 5 10 6 9 CS61600 MASTER 8 7 1 14 V+ 2 13 OVR 3 12 V+ DIN 1 NC 4 11 NC V+ NC 5 10 NC NC CLKOUT DOUT 1 10k ARE 6 CS61600 7 SLAVE 9 DIN 2 ARC multiple slaves may be added DOUT 2 8 CLKIN Figure A2. Master / Slave configuration gether. After the power supplies have stabilized, and the clock has been input at CLKIN, FIFORST should be momentarily pulled low to reset the pointers of both devices. The overflow flags should then be reset by momentarily pulling RESET, pin 1, low. Additional slaves may be added. The ARC input may be derived from either the CLKOUT pin on the master, or the CLKOUT pin on a preceding slave. When using the master’s CLKOUT pin, the fan out must be considered. Attaching several inputs to the CLKOUT pin increases the load that the output must drive. The added capacitance will reduce the switching speed of the output driver. Similarly, a configuration which uses the CLKOUT signal of each CS61600 to drive the subsequent CS61600 will induce some propagation delay. These potential timing problems should be considered when cascading CS61600s. shows one method for maintaining the CLKOUT signal. The reference clock is a locally generated clock whose frequency lies within the tolerance of the applicable specifications which govern the system’s design. When the CLKIN signal goes away, the multiplexor should switch in the reference clock. Since this clock goes through the jitter attenuator, phase and frequency integrity at CLKOUT is maintained. Jitter Attenuation at Different Clock Rates The CS61600 can be used to attenuate jitter at frequencies below 2.048 MHz. For signal frequencies above about 900 kHz, selection of the appropriate crystal will suffice. For jitter attenuLOCALLY GENERATED REFERENCE CLOCK 1.544 MHz MULTIPLEXER CLKIN pin 8 CLKOUT pin 10 CS61600 Maintaining Clock RECOVERED CLOCK 1.544 MHz Many applications require that the clock signal from CLKOUT be maintained within some specified range of frequencies when the clock signal on CLKIN (often generated from a recovered T1 signal clock) goes away. Figure A3 DS9F3 LOSS OF CLOCK DETECTOR Figure A3. Maintaining Clock Integrity 11 CS61600 ation of lower frequency signals, an external divider is required. Figure A4 shows how the CS61600 can be configured for low frequency jitter attenuation. Frequency tolerance of the input signal is still based on the pull range of the crystal in ppm. For example, a 64 kbps jitter attenuator which uses an external divide by 32, and a 8.192 MHz crystal with ± 200 ppm pull range will have + 200 ppm tolerance at 64 kbps or + 12.8 Hz. 12 V+ RESET FIFORST 4.5 MHz to 8.2 MHz V+ +5V 10k 10k 200k 10k ARE 1 14 2 13 3 12 4 11 5 10 6 9 DOUT 1 8 CLKIN 7 CS61600 DIN 1 ARC DIVIDER OSCOUT CLKOUT Figure A4. Low Clock Frequency Jitter Attenuation DS9F3 14 PIN PLASTIC (PDIP) PACKAGE DRAWING eB D eC E E1 1 TOP VIEW A2 A SEATING PLANE A1 ∝ e b1 INCHES ∝ MIN 0.000 0.015 0.115 0.014 0.045 0.008 0.735 0.300 0.240 0.090 0.280 0.300 0.000 0.115 0° eA c b BOTTOM VIEW DIM A A1 A2 b b1 c D E E1 e eA eB eC L L MAX 0.210 0.025 0.195 0.022 0.070 0.014 0.775 0.325 0.280 0.110 0.320 0.430 0.060 0.150 15° SIDE VIEW MILLIMETERS MIN MAX 0.00 5.33 0.38 0.64 2.92 4.95 0.36 0.56 1.14 1.78 0.20 0.36 18.67 19.69 7.62 8.26 6.10 7.11 2.29 2.79 7.11 8.13 7.62 10.92 0.00 1.52 2.92 3.81 0° 15° 8/24/99 : CIRRUS LOGIC --- CRYSTAL SEMICONDUCTOR : 14 PIN PLASTIC (PDIP) PACKAGE DRAWING Contacting Cirrus Logic Support For a complete listing of Direct Sales, Distributor, and Sales Representative contacts, visit the Cirrus Logic web site at: http://www.cirrus.com/corporate/contacts/ Preliminary product information describes products which are in production, but for which full characterization data is not yet available. Advance product information describes products which are in development and subject to development changes. Cirrus Logic, Inc. has made best efforts to ensure that the information contained in this document is accurate and reliable. However, the information is subject to change without notice and is provided “AS IS” without warranty of any kind (express or implied). No responsibility is assumed by Cirrus Logic, Inc. for the use of this information, nor for infringements of patents or other rights of third parties. This document is the property of Cirrus Logic, Inc. and implies no license under patents, copyrights, trademarks, or trade secrets. No part of this publication may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photographic, or otherwise) without the prior written consent of Cirrus Logic, Inc. Items from any Cirrus Logic website or disk may be printed for use by the user. However, no part of the printout or electronic files may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photographic, or otherwise) without the prior written consent of Cirrus Logic, Inc.Furthermore, no part of this publication may be used as a basis for manufacture or sale of any items without the prior written consent of Cirrus Logic, Inc. The names of products of Cirrus Logic, Inc. or other vendors and suppliers appearing in this document may be trademarks or service marks of their respective owners which may be registered in some jurisdictions. A list of Cirrus Logic, Inc. trademarks and service marks can be found at http://www.cirrus.com.