AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS PRELIMINARY APPLICATION NOTE Phase Lock Loop Configurations for the Semtech ACS8530 SONET and SDH SETS Device Overview This Application Note describes some examples of the ways in which the ACS8530 Phase Lock Loops (PLL) can be configured for different frequency and output jitter options. Revision 1.01/April 2002 © Semtech Corp. Page 1 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS APPLICATION NOTE Table of Contents List of Sections Page 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 2 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 2.1 T0 DPLL Architecture and Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 2.2 T4 DPLL Architecture and Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 2.3 Default Configuration for Independent T4 and T0 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 2.4 Alternative Configuration for Independent T0 and T4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . .10 2.5 Configuration for Low Jitter E3/DS3 and OC-N Clock Generation with No Independent T4 Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 2.6 Configuration for Low Jitter E3/DS3 and E1/DS1 with No Independent T4 Path . . . . . . . . . .12 2.7 T4 PLL Configured to Measure the Relative Phase Error between Inputs . . . . . . . . . . . . . . . .13 2.7.1 Examples of T4 PFD used for Phase Measurement . . . . . . . . . . . . . . . . . . . . . . . . . .15 2.8 T4 Low Frequency Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Appendix 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 List of Figures Figure 1 ACS8530 PLL Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Figure 2 Basic T0 configuration for OC-N and n x E1/DS1 outputs (low and high jitter). . . . . . . . . . . . .6 Figure 3 Basic T4 configuration for independent BITS/SSU output. . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Figure 4 T4 configuration for low jitter independent BITS/SSU and OC-N clock outputs. . . . . . . . . . . .8 Figure 5 Default configuration of the T0 and T4 PLLs for simultaneous clock output.. . . . . . . . . . . . . .9 Figure 6 Alternative configuration for independent T0 and T4 outputs. . . . . . . . . . . . . . . . . . . . . . . . .10 Figure 7 Configuration for low jitter E3/DS3 and OC-N clock generation with no independent T4 path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Figure 8 Configuration for low jitter E3/DS3 and E1/DS1 with no independent T4 path. . . . . . . . . . .12 Figure 9 T4 PFD configured to perform Phase Offset Measurement between selected T0 input and a standby. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 List of Tables Table 1 Table 2 Table 3 Phase measurement examples using T4 PFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 T0 DPLL Frequency Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 T4 DPLL Frequency Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 Revision 1.01/April 2002 © Semtech Corp. Page 2 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS 1 APPLICATION NOTE Introduction This Application Note describes some examples of the ways in which the ACS8530 Phase Lock Loops (PLL) can be configured for different frequency and output jitter options. The ACS8530 has two independent PLL "paths" on the same chip, one denoted the T0 path and the other the T4 path. The T0 path is a combination of a Digital PLL (DPLL) and an Analog PLL (APLL). The T4 path is also a combination of a DPLL and an APLL, but the DPLL can be configured to function independently from the APLL. The T0 path is a high quality, highly configurable path designed to provide features necessary for node timing synchronization within a SONET/SDH network. The T4 path is a simpler and less configurable path designed to give a totally independent path for internal equipment synchronization. The device supports use of either or both paths, either locked together or independent. The basic PLL architecture of the ACS8530 is shown in Figure 1. 2 General A DPLL gives a stable and consistent level of performance that can be easily programmed for different dynamic behaviour or operating range. Digital synthesis is used to generate all required SONET/SDH output frequencies. The digital logic operates at 204.8 MHz that is multiplied up from the external 12.8 MHz oscillator module. Hence the best resolution of the output signals from the DPLL is one 204.8 MHz cycle or 4.9 ns. Additional resolution and lower final output jitter is provided by a de-jittering APLL that reduces the 4.9 ns pk-pk jitter from the digital down to 350 ps pk-pk and 50-60 ps RMS as typical final outputs measured broadband (from 10 Hz to 1 GHz). This arrangement combines the advantages of the flexibility and repeatability of a DPLL with the low jitter of an APLL. Figure 1 T4 Reference Input ACS8530 PLL Architecture Lock_T4_to_T0 Sts_Current_Phase Control T4_DPLL_Frequency T4_APLL_for_T0 0 Forward DFS PFD and Loop Filter 0 T4_Dig_Feedback T0_DPLL_Freq 1 1 1 T4 Output Dividers T4 Output APLL TO1 to TO7 0 T4 DPLL Locking Frequency Feedback DFS T4_Op_From_TO 0 0 1 TO8 /TO9 8 kHz T0_DPLL_Frequency Control 0 77M Output DFS Sts_Current_Phase T0 Reference Input PFD and Loop Filter PBO Phase Offset 1 LF Output DFS 0 T0_DPLL_Frequency Control 77M Forward DFS 1 1 T0 Output APLL T0 Output Dividers TO1 to TO7 TO1 to TO7 TO10/TO11 T0 Feedback APLL 1 Locking Frequency Feedback DFS 0 T0 DPLL Analog F8530D_017BLOCKDIA_04 Revision 1.01/April 2002 © Semtech Corp. Page 3 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS APPLICATION NOTE The DPLLs in the ACS8530 are uniquely very programmable for all PLL parameters of bandwidth (from 0.5 mHz up to 70 Hz), damping factor (from 1.2 to 20), frequency acceptance and output range (from 0 to 80 ppm, typically 9.2 ppm), input frequency (12 common SONET/SDH spot frequencies) and input-tooutput phase offset (in 6 ps steps up to 200 ns). There is no requirement to understand the loop filter equations or detailed gain parameters since all high level factors such as overall bandwidth can be set directly via registers in the microprocessor interface. The T0 path DPLL by default always produces an output at 77.76 MHz to feed the APLL, regardless of the frequency selected at the output pins. The T4 path can be operated at a number of frequencies. This is to enable the generation of extra output frequencies, which cannot be easily related to 77.76 MHz. When the T4 path is selected to lock to the T0 path, the T4 DPLL locks to the 8 kHz from the T0 DPLL. This is because all of the frequencies of operation of the T4 path can be divided to 8 kHz and this will ensure synchronization of all the frequencies within the two paths. Both the DPLL's outputs are connected to multiplying and filtering APLLs. The outputs of these APLLs are divided making a number of frequencies simultaneously available for selection at the output clock ports. The various combinations of DPLL, APLL and divider configurations allow for generation of a comprehensive set of frequencies, as listed in ACS8530 datasheet. To synchronize the lower output frequencies when the T0 PLL is locked to a high frequency reference input, an additional input is provided. The SYNC2K pin (pin 45) is used to reset the dividers that generate the 2 kHz and 8 kHz outputs such that the output 2/8 kHz clocks are precisely aligned with the input 2 kHz. The T4 DPLL is similar in structure to the T0 DPLL, but since the T4 is only providing a clock synthesis and input to output frequency translation function, with no defined requirement for jitter attenuation or input phase jump absorption, then its bandwidth is limited to the high end and the T4 does not incorporate any of the Phase Build-out and adjustment facilities of the T0 DPLL. The T0 and T4 PLL paths support the following common features: z Automatic source selection according to input priorities and quality level. z Different quality levels (activity alarm thresholds) for each input. z Variable bandwidth, lock range and damping factor. z Direct PLL locking to common SONET/SDH input frequencies or any multiple of 8 kHz. z Automatic mode switching between Free run, Locked and Holdover states. z Fast detection on input failure and entry into Holdover mode (holds at the last good frequency value). z Frequency translation between input and output rates via direct digital synthesis. z Multi-cycle phase detection and locking, programmable up to +/-8192 UI for improved jitter tolerance in direct lock mode. z Multiple n x E1/DS1 outputs supported. Revision 1.01/April 2002 © Semtech Corp. Page 4 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS 2.1 APPLICATION NOTE T0 DPLL Architecture and Features The main features of the T0 DPLL are: z Programmable DPLL bandwidth in 18 steps from 0.5 mHz to 70 Hz. z Programmable damping factor for optional faster locking and peaking control. Factors = 1.2, 2.5, 5, 10 or 20. z Multiple phase lock detectors. z Phase Build-out on source switch (hitless source switching, +/- 2.5 ns). z Input to output Phase offset adjustment (Master/Slave), +/- 200 ns range, 6ps resolution step size. z Phase Build-out phase offset adjustment (source switch), +/- 3 ns range, 5ps resolution step size. z Detection of phase jump on the current locked to source: programmable limit from 1 - 3.5 us in 100 ms. z Optional automatic Phase Build-out event on a detected input phase jump. z Holdover frequency averaging with a choice of average times, 3rd Order anti-aliasing filter, read-out of filtered value. z Low jitter MFrSync (2 kHz) and FrSync (8 kHz) outputs. z Revertive and non-revertive mode. The control of the T0 DPLL is either via software or an internal state machine control. The basic configuration for the T0 PLL is shown in Figure 2. The T0 DPLL always produces 77.76 MHz regardless of either the reference frequency (frequency at the input pin of the device) or the locking frequency (frequency at the input of the DPLL Phase and Frequency Detector- PFD). The input reference is either passed directly to the PFD or via a pre-divider (not shown) to produce the reference input. The feedback 77.76 MHz is either divided or synthesized to generate the locking frequency. Digital Frequency Synthesis (DFS) is a technique for generating an output frequency using a higher frequency system clock. However, the edges of the output clock are not ideally placed in time, since all edges of the output clock will be aligned to the active edge of the 204.8 MHz system clock. This will mean that the generated clock will inherently have jitter on it equivalent to one period of the 204.8 MHz system clock. The T0 77.76 MHz forward DFS block uses DFS clocked by the 204.8 MHz system clock to synthesize the 77.76 MHz and, therefore, has an inherent 4.9 ns of pk-pk jitter. There is an option to use an APLL, the T0 feedback APLL, to filter out this jitter before the 77.76 MHz is used to generate the feedback locking frequency in the T0 feedback DFS block. This analog feedback option allows a lower jitter (<1 ns) feedback signal to give maximum performance. The digital feedback option is present so that when the output path is switched to digital feedback the two paths remain synchronized. The T0 77.76 MHz forward DFS block is also the block that handles Phase Build-out and any phase offset programmed into the device. Hence, the T0 77.76 MHz forward DFS and the T0 77.76 MHz output DFS blocks are locked in frequency but may be offset in phase. The T0 77.76 MHz output DFS block also uses the 204.8 MHz system clock and always generates 77.76 MHz for the output clocks (with inherent 4.9 ns of jitter). This is fed to another DFS block and to the T0 output APLL. The low frequency T0 LF output DFS block is used to produce three frequencies; two of them, Digital1 and Digital2, are available for selection to be produced at outputs TO1-TO7, and the third frequency can produce multiple E1/DS1 rates via the filtering APLLs. The input clock to the T0 LF output DFS block is either 77.76 MHz from the T0 output APLL (post jitter filtering) or 77.76 MHz direct from the T0 77.76 MHz output DFS. Utilizing the clock from the output of the APLL will result in lower jitter outputs from the T0 LF output DFS block. However, when the input to the APLL is taken from the T0 LF output Revision 1.01/April 2002 © Semtech Corp. Page 5 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS APPLICATION NOTE DFS block, the input to that block comes directly from the T0 77.76 MHz output DFS block so that a "loop" is not created. The T0 output APLL is for multiplying and filtering. The input to the T0 output APLL can be either 77.76 MHz from the T0 77.7 6MHz output DFS block or an alternative frequency from the T0 LF output DFS block (offering 77.76 MHz, 12 x E1, 16 x E1, 16 x DS1 or 24 x DS1). The frequency from the T0 output APLL is 4 times it's input frequency i.e. 311.04 MHz when used with a 77.76 MHz input. The T0 output APLL is subsequently divided by 1, 2, 4, 6, 8, 12, 16 or 48, and these are available at the TO1TO7 outputs. Figure 2 Basic T0 configuration for OC-N and n x E1/DS1 outputs (low and high jitter). path 7 2.2 T4 DPLL Architecture and Features The main features of the T4 DPLL are: z Programmable DPLL bandwidth in 3 steps from 18, 35 and 70 Hz. z Programmable damping factor: For optional faster locking and peaking control. Factors = 1.2, 2.5, 5, 10 or 20. z Multiple phase lock detectors. z Multi-cycle phase detection and locking, programmable up to +/-8192 UI - improves jitter tolerance in direct lock mode. z N x E1/DS1 including 12 x E1, 16 x E1, 16 x DS1 and 24 x DS1 supported. z E3/DS3 (44.736 MHz/34.368 MHz) support. z Low jitter N x E1/DS1 options. z Low jitter MFrSync (2 kHz) and FrSync (8 kHz) outputs. z Can use the T4 DPLL as an Independent FrSync DPLL. Revision 1.01/April 2002 © Semtech Corp. Page 6 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS APPLICATION NOTE The T4 path is much simpler than the T0 path - see Figure 3. This path offers no Phase Build-out or phase offset. The T4 input can be used to either lock to a reference clock input independent of the T0 path, or lock to the T0 path. Unlike the T0 path, the T4 forward DFS block does not always generate 77.76 MHz. The possible frequencies are listed in Appendix description for Register 64. Similarly to the T0 path, the output of the T4 forward DFS block is generated using DFS clocked by the 204.8 MHz system clock and will have an inherent jitter of 4.9 ns. The T4 feedback DFS also has the facility to be able to use the post APLL (jitter-filtered) clock to generate the feedback locking frequency. Again, this will give the maximum performance by using a low jitter feedback, see Figure 4. The T4 output APLL block is also for multiplying and filtering. The input to the T4 output APLL can come either from the T4 forward DFS block or from the T0 path. These configurations are described in more detail in later sections. Figure 3 Basic T4 configuration for independent BITS/SSU output. path8 Revision 1.01/April 2002 © Semtech Corp. Page 7 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS Figure 4 APPLICATION NOTE T4 configuration for low jitter independent BITS/SSU and OC-N clock outputs. path1 The input to the T4 output APLL can be programmed to be one of the following: z Output from the T4 forward DFS block z 12 x E1 from T0 z 16 x E1 from T0 z 16 x DS1 from T0 z 24 x DS1 from T0 The T4 path can be operated at a number of frequencies. This is to enable the generation of extra output frequencies, which cannot be easily related to 77.76 MHz. When the T4 path is selected to lock to the T0 path, the T4 DPLL locks to the 8 kHz from the T0 DPLL. This is because all of the frequencies of operation of the T4 path can be divided to 8 kHz and this will ensure synchronization of all the frequencies within the two paths. The frequency generated from the T4 output APLL block is four times its input frequency i.e. 311.04 MHz when used with a 77.76 MHz input. The T4 output APLL is subsequently divided by 2, 4, 8, 12, 16, 48 and 64 and these are available at the TO1-TO7 outputs. The TO8 and TO9 outputs are driven from either the T4 or the T0 path. The TO10 and TO11 outputs are always generated from the T0 path. Reg.7A Bit 7 selects whether the source of the 2 kHz and 8 kHz outputs available from TO1-TO7 is derived from either the T0 or the T4 paths. Revision 1.01/April 2002 © Semtech Corp. Page 8 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS 2.3 APPLICATION NOTE Default Configuration for Independent T4 and T0 Paths The default configuration for the ACS8530 for the T0 and T4 paths to produce simultaneous independent clock outputs is shown in Figure 5. This configuration will yield high jitter BITS/AMI clocks from the T4 path. In addition, the T4 APLL will yield low jitter OC-N clocks. The T0 path will yield low jitter OC-N, clocks and high jitter n x E1/DS1 simultaneously. Figure 5 Default configuration of the T0 and T4 PLLs for simultaneous clock output. Must use LOCK8K The register settings for the default configuration are as follows: Reg 35 bit 7 = 0 Reg 35 bit 6 = 1 Reg 35 bit 4 = 0 Reg 64 bit (2:0) = 001, see Table 3 Reg 65 bit 7 = 0 Reg 65 bit 6 = 0 Reg 65 bit (5:4) = 00 Reg 65 bit (2:0) = 000, see Table 2 Revision 1.01/April 2002 © Semtech Corp. Page 9 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS 2.4 APPLICATION NOTE Alternative Configuration for Independent T0 and T4 Paths An alternative configuration for the ACS8530 for independent T0 and T4 paths to produce simultaneous clock outputs is shown in Figure 6. This configuration will yield high jitter BITS/AMI outputs from the T4 path. The T0 path will yield low jitter OC-N and high jitter n x E1/DS1 plus a low jitter version of the n x E1/DS1 from the T4 APLL. Figure 6 Alternative configuration for independent T0 and T4 outputs. Configure for 16E1 or 16DS1 mode for lower jitter BITS/AMI path2 The register settings for the configuration described are as follows: Reg 35 bit 7 = 0 Reg 35 bit 6 = 1 Reg 35 bit 4 = 0 Reg 64 bit (2:0) = 12 E1 (010), 16 E1 (011), 16 DS1 (101) or 24 DS1 (100), see Table 3 Reg 65 bit 7 = 0 Reg 65 bit 6 = 1 Reg 65 bit (5:4) = 12 E1 (00), 16 E1 (01), 16 DS1 (11) or 24 DS1 (10), see Table 2 Reg 65 bit (2:0) = 000 Revision 1.01/April 2002 © Semtech Corp. Page 10 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS 2.5 APPLICATION NOTE Configuration for Low Jitter E3/DS3 and OC-N Clock Generation with No Independent T4 Path The configuration for the ACS8530 for E3/DS3 generation, where the T0 and T4 paths are locked to the T0, is shown in Figure 7. This configuration will yield low jitter E3/DS3 outputs from the T4 path. The T0 path will yield low jitter OC-N and high jitter n x E1/DS1. Figure 7 Configuration for low jitter E3/DS3 and OC-N clock generation with no independent T4 path. Configure for E3/DS3 mode as required path4 The register settings for the configuration described are as follows: Reg 35 bit 7 = 1 Reg 35 bit 6 = 0 Reg 35 bit 4 = x Reg 64 bit (2:0) = E3 (110) or DS3 (111), see Table 3 Reg 65 bit 7 = 0 Reg 65 bit 6 = 0 Reg 65 bit (5:4) = xx Reg 65 bit (2:0) = 000, see Table 2 Revision 1.01/April 2002 © Semtech Corp. Page 11 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS 2.6 APPLICATION NOTE Configuration for Low Jitter E3/DS3 and E1/DS1 with No Independent T4 Path The configuration for the ACS8530 where the T0 and T4 paths are locked to the T0 is shown in Figure 8. This configuration will yield low jitter E3/DS3 outputs from the T4 path. The T0 path will yield low jitter n x E1/DS1. Figure 8 Configuration for low jitter E3/DS3 and E1/DS1 with no independent T4 path. Configure for E3/DS3 mode as required path 5 Note... Digital feedback is required to match digital output, for synchronization reasons The register settings for the configuration described are as follows: Reg 35 bit 7 = 1 Reg 35 bit 6 = 0 Reg 35 bit 4 = x Reg 64 bit (2:0) = E3 (110) or DS3 (111), see Table 3 Reg 65 bit 7 = 0 Reg 65 bit 6 = 0 Reg 65 bit (5:4) = xx Reg 65 bit (2:0) = 12 E1 (010), 16 E1 (011), 16 DS1 (101) or 24 DS1 (100), see Table 2 Revision 1.01/April 2002 © Semtech Corp. Page 12 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS 2.7 APPLICATION NOTE T4 PLL Configured to Measure the Relative Phase Error between Inputs The T4 DPLL PFD can be configured to measure the phase difference of the currently locked to input on the T0 DPLL with respect to any other valid input. The T4 DPLL PFD compares two inputs (usually the feedback and reference input) with each other and performs some filtering. This filtering has a bandwidth of approx. 100 Hz. This will result in a digital number representing the filtered phase difference between these two signals being available (normally used for the digital synthesis). The phase difference is reported in units of 0.707 degrees of the actual locking frequency. When direct locking to high frequency input, the actual time is then scaled down and will give resolution down to e.g. 110 ps at 19.44 MHz in direct locking mode compared with 245 ns with Lock8K mode enabled with the same 19.44 MHz input. The two inputs to the PFD have to be very close in frequency to give an accurate phase measurement. The phase difference measurement is held in the 16 bit register, sts_current_phase. The register is updated on a 204.8 MHz cycle. Under normal circumstances the frequency of the inputs to the PFD are determined by the input frequency selection and the pre-divider mode settings such as Lock8K and DivN. The appropriate feedback frequency is automatically selected from the supported spot frequencies to match the input reference frequency (post division if necessary). The feature to use the T4 PFD to measure the relative phase error between the selected T0 input and the selected T4 input will require the user to ensure that the settings and frequency are the same for the two inputs to be measured. Enabling the feature simply replaces the T4 DPLL feedback signal to the T4 PFD with the T0 PFD input reference signal. Reading the current phase register from the T4 path will yield the filtered phase difference between the two inputs. If there is jitter or wander present on either or both inputs, then this will have an effect on the measured phase. The extent of this effect will depend on the frequency of the jitter/wander compared to the 100 Hz bandwidth of the filter. The T4 PFD configuration is shown in Figure 9. Revision 1.01/April 2002 © Semtech Corp. Page 13 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS Figure 9 APPLICATION NOTE T4 PFD configured to perform Phase Offset Measurement between selected T0 input and a standby. Select stand-by source path6 The register settings for the configuration described are as follows: Reg 35 bit 7 = 0 Reg 35 bit 6 = x Reg 35 bit 4 = x Reg 64 bit (2:0) = xxx Reg 65 bit 7 = 1 Reg 65 bit 6 = 1 (if required) Reg 65 bit (5:4) = 12 E1 (00), 16 E1 (01), 16 DS1 (11) or 24 DS1 (10) - see Table 1 Reg 65 bit (2:0) = 000 Revision 1.01/April 2002 © Semtech Corp. Page 14 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS 2.7.1 APPLICATION NOTE Examples of T4 PFD used for Phase Measurement Table 1 gives examples of possible outcomes when T4 PFD used to measure phase between two valid input reference sources, where the ACS8530 has following valid inputs: I1 I2 I3 I4 I5 I6 I7 I8 I9 I10 I11 I12 I13 I14 inactive inactive 19.44 MHz, direct locking 19.44 MHz, direct locking 77.76 MHz, Lock8K enabled 77.76 MHz, Lock8K enabled 2.048 MHz, direct locking 2.048 MHz, direct locking 10 MHz, DivN to 8 kHz enabled 10 MHz, DivN to 8 kHz enabled inactive inactive inactive inactive Table 1 Phase measurement examples using T4 PFD Example T0 Path Input Selection Case 1 I3 Case 2 I5 Case 3 Case 4 2.8 I3 I3 T4 Input Selection I4 Result/Problems Meaningful result Any other input Result not meaningful I6 Can measure result, but phase error in 245 ns resolution due to locking at 8 kHz (period of 77.76 MHz is 13 ns) Any other input Result not meaningful I8 Meaningful result Any other input Result not meaningful I10 Can measure result, but phase error in 245 ns resolution due to locking at 8 kHz (period of 10 MHz is 100 ns) Any other input Result not meaningful T4 Low Frequency Outputs The TO8 output is an AMI composite clock output. This always produces a 64 kHz/8 kHz composite clock. TO9 always produces an E1/DS1 frequency output for a BITS/SSU application. Both TO8 and TO9 are generated by DFS within either the T0 or T4 path, as controlled by Register 35 Bit 4. The frequencies generated from TO8 and TO9 are independent of the mode (frequency) of either the T4 or the T0 paths. The amount of jitter generated on the TO8 and TO9 outputs will be related to the clock period of the source DFS block added to any jitter present on that clock. This is detailed in the following text. As can be seen in the block diagram in Figure 1, the DFS blocks used to generate these outputs are the T4 feedback DFS block in the case of the T4 path and the T0 LF output DFS block for the T0 path. The T4 feedback DFS block is clocked by the T4 forward DFS, or its APLL. The frequency of the T4 forward DFS block can be determined by referring to the ACS8530 data sheet, Table 13 (T4 APLL frequencies). This is in the region of 65 MHz to 89 MHz and can be approximated to have a period of between 11 ns and 15 ns. The output of the T4 forward DFS block will have an inherent pk-pk jitter of approximately 4.9 ns. Revision 1.01/April 2002 © Semtech Corp. Page 15 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS APPLICATION NOTE The clock to the T4 feedback DFS block will have <1 ns of jitter when the T4 path is in analog feedback mode (Reg. 35 Bit 6 = 0). However, it will have 4.9 ns when in digital feedback mode. The TO8 output, being 64 kHz/8 kHz, can be directly divided from the clock to the T4 feedback DFS block; therefore, it will have a similar amount of jitter on it, i.e. <1 ns when using analog feedback, and 4.9 ns when using digital feedback. The TO9 output will have more jitter because it is synthesized from the clock to the T4 feedback DFS block. The jitter, in addition to that present on the clock to the T4 feedback DFS block, will be equivalent to a period of that clock, i.e. between 11 ns and 15 ns. The jitter present on the TO9 output will range from 11 ns (when the T4 path is in DS3 mode - 89 MHz combined with analog feedback) to 20 ns (when in 16 x E1 mode - 65 MHz combined with digital feedback). Appendix 1 Register definitions for configuration of the T0 and T4 paths used in the text, the default is in BOLD. Register 35 - cnfg_T4_Path Bit 7 Lock_T4_to_T0 Bit selects either the T4 direct inputs, or T0 DPLL as the input of the T4 path. This allows the T4 DPLL to be used to produce different sets of frequencies to the T0 DPLL but still maintain lock. Bit 6 0 T4 path locks independently from the T0 path. 1 T4 DPLL locks to the output of the T0 DPLL. T4_dig_feedback Bit to select digital feedback mode for the T4 DPLL. 0 T4 DPLL in analog feedback mode. 1 T4 DPLL in digital feedback mode. Bit 5 Not used. Bit 4 T4_op_from_T0 0 T08 and T09 will be generated from T4 DPLL. 1 T08 and T09 will be generated from T0 DPLL. Revision 1.01/April 2002 © Semtech Corp. Page 16 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS APPLICATION NOTE Register 64 - cnfg_T4_PLL_Freq Bits [2:0] T4_DPLL_frequency Register to configure the frequency of operation of the DPLL in the T4 path. The frequency of the DPLL will also affect the frequency of the T4 APLL which, in turn, affects the frequencies available at outputs TO1 - TO7. It is also possible to not use the T4 DPLL at all, but use the T4 APLL to run directly from the T0 DPLL output, see Register 65 (cnfg_T0_DPLL_frequency). 000 T4 DPLL squelched (clock off). 001 77.76 MHz (OC-N rates), T4 APLL frequency = 311.04 MHz. 010 12E1, T4 APLL frequency = 98.304 MHz. 011 16E1, T4 APLL frequency = 131.072 MHz. 100 24DS1, T4 APLL frequency = 148.224 MHz. 101 16DS1, T4 APLL frequency = 98.816 MHz. 110 E3, T4 APLL frequency = 274.944 MHz. 111 DS3, T4 APLL frequency = 178.944 MHz. Register 65 - cnfg_T0_DPLL_Frequency Bit 7 T4_meas_T0_ph Register bit to control the feature to use the T4 path to measure phase offset from the T0 path. When enabled the T4 path is disabled and the phase detector is used to measure the phase between the input to the T0 DPLL and the selected T4 input. Bit 6 0 Normal - T4 Path normal operation. 1 T4 DPLL disabled, T4 phase detector used to measure phase between selected T0 input and selectedT4 input. T4_APLL_for_T0 Register bit to select whether the T4 APLL takes its input from the T4 DPLL or the T0 DPLL. If the T0 DPLL is selected then the frequency is controlled by Bits [5:4], T0_freq_to_T4_APLL. 0 T4 APLL takes its input from the T4 DPLL. 1 T4 APLL takes its input from the T0 DPLL. Bits [5:4] T0_freq_to_T4_APLL Register to select the T0 frequency driven to the T4 APLL when selected by Bit 6, T4_APLL_for_T0. 00 12E1, T4 APLL frequency = 98.304 MHz. 01 16E1, T4 APLL frequency = 131.072 MHz. 10 24DS1, T4 APLL frequency = 148.224 MHz. 11 16DS1, T4 APLL frequency = 98.816 MHz. Revision 1.01/April 2002 © Semtech Corp. Page 17 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS Bit 3 APPLICATION NOTE Not used Bits [2:0] T0_DPLL_frequency Register to configure the frequency of operation of the DPLL/APLL in the T0 path. This register affects the frequencies available at outputs TO1 - TO7, see Reg. 60 - Reg. 63. 000 77.76 MHz, digital feedback, T0 APLL frequency = 311.04 MHz. 001 77.76 MHz, analog feedback, T0 APLL frequency = 311.04 MHz. 010 12E1, T0 APLL frequency = 98.304 MHz. 011 16E1, T0 APLL frequency = 131.072 MHz. 100 24DS1, T0 APLL frequency = 148.224 MHz. 101 16DS1, T0 APLL frequency = 98.816 MHz. 110 Not used. 111 Not used. Table 2 T0 DPLL Frequency Configurations T0 DPLL Mode OC-N Frequencies available for selection at the outputs TO1-TO7 (MHz) 311.04 155.52 77.76 51.84 38.88 25.92 19.44 6.144 6.48 12E1 98.304 49.152 24.576 16.384 12.288 8.192 16E1 131.072 65.536 32.768 21.84533 16.384 10.922667 8.192 2.7306667 24DS1 148.224 74.112 37.056 24.704 18.528 12.352 3.088 16DS1 98.816 49.408 24.704 16.46933 12.352 8.2346667 6.176 9.264 2.048 2.0586667 Table 3 T4 DPLL Frequency Configurations T4 DPLL Mode Frequencies available for selection at the outputs TO1-TO7(MHz) OC-N 155.52 77.76 38.88 19.44 6.48 4.86 12E1 49.152 24.576 12.288 6.144 2.048 1.536 16E1 65.536 32.768 16.384 8.192 2.7306667 2.048 24DS1 74.112 37.056 18.528 9.264 3.088 2.316 16DS1 49.408 24.704 12.352 6.176 2.0586667 1.544 E3 137.472 68.736 34.368 17.184 5.728 4.296 DS3 89.472 44.736 22.368 11.184 3.728 2.796 Revision 1.01/April 2002 © Semtech Corp. Page 18 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS APPLICATION NOTE Notes Revision 1.01/April 2002 © Semtech Corp. Page 19 www.semtech.com AN-SETS-7 PLL Configurations for ACS8530 ADVANCED COMMUNICATIONS APPLICATION NOTE Revision History Revision Date Reference Description of changes 1.0 11/Apr/2002 All pages First draft 1.01 16/Apr/2002 All Pages 2.1 bullets 4 & 5 New format phase offset adjustment- resolution steps updated Contacts For Additional Information, contact the following: Semtech Corporation Advanced Communications Products E-mail: [email protected] Internet: http://www.semtech.com USA: Mailing Address: Street Address: Tel: +1 805 498 2111, [email protected] P.O. Box 6097, Camarillo, CA 93011-6097 200 Flynn Road, Camarillo, CA 93012-8790 Fax: +1 805 498 3804 FAR EAST: 11F, No. 46, Lane 11, Kuang Fu North Road, Taipei, R.O.C. Tel: +886 2 2748 3380 Fax: +886 2 2748 3390 EUROPE: Semtech Ltd., Units 2 and 3, Park Court, Premier Way, Abbey Park Industrial Estate, Romsey, Hampshire, SO51 9AQ Tel: +44 (0)1794 527 600 Fax: +44 (0)1794 527 601 ISO9001 CERTIFIED Revision 1.01/April 2002 © Semtech Corp. Page 20 www.semtech.com