Recommended Crystal, TCXO, and OCXO Reference Manual for High-Performance Jitter Attenuators and Clock Generators(One of them)

Recommended Crystal, TCXO, and OCXO Reference Manual for High-Performance   Jitter Attenuators and Clock Generators

The purpose of this document is to provide a list of crystals, TCXOs, and OCXOs which have been tested and qualified for use with Silicon Labs high-performance jitter

attenuators and clock generators. Changes to this document will be accompanied by a Process Change Notice (PCN).

The information presented here is based on tested samples. Customers should monitor specification compliance and quality over time. Customers should also verify that the

selected crystal or oscillator is a good match for their application.

Please refer to relevant data sheets, reference manuals, and application note, "AN905: Si534x External References: Optimizing Performance", for external reference layout rec- ommendations.

• Si534x Reference Manuals

• Si538x Reference Manuals

• Si539x Reference Manuals

• AN905: Si534X External References: Optimizing Performance

• AN1093: Achieving Low Jitter Using an Oscillator Reference with the Si5342-47 Jitter Attenuators

• Si5340/41/91 clock generators

• Si5342-47, Si5392-97 Jitter cleaners

• Si5342H/44H/71/72 Coherent optics clocks

• Si5348/83/83 SyncE clocks

• Si5380/81/86 Wireless clocks

Recommended Crystal, TCXO, and OCXO Reference Manual for High-Performance Jitter Attenuators and Clock Generators

Recommended Crystals

1.  Recommended Crystals

A crystal (XTAL) in timing refers to a quartz crystal that works on the piezo-electric effect: an electrical voltage across it causes a me- chanical perturbation and this in turn causes an electrical voltage to develop across it. The XTAL needs to be driven by a circuit to sustain its oscillation. This provides a stable source of frequency and is used as a reference in phase locked loops.

The table below lists the presently recommended XTALs. XTALs that meet the specifications outlined in this document may be submit- ted to Silicon Labs for future qualification for use with the Si534x/7x/9x/83/84/88/89 clocks. Most of the part numbers in this table are custom generated for Silicon Labs. Part Family information is included in the table to enable searching through vendor websites. Users can also contact the vendor directly and ask for the specific part number listed.

Table 1.1.  Recommended XTALS for All Si534x/7x/9x/83/84/88/89 Devices

Refer to Appendix A for information on XTAL specifications and how to choose the best XTAL for your application. In general, a XTAL meeting the requirements of the ESR vs. C0 figures in Appendix A and having a max power rating as specified in the applicable data sheet is guaranteed to oscillate.

For Silicon Labs Si534x/7x/9x P/Q grade devices, choose a XTAL that has a total lifetime accuracy of less than 100 ppm. This number includes initial offset, aging at hot temperature (85°C), temperature stability, pulling sensitivity, effects of reflow, and activity dips.

Some applications may require XTALs that have been tested incrementally over the entire temperature range to ensure that the change in XTAL resonant frequency over any 2 °C temperature difference is bounded. This is called testing for activity dips and can add cost to the XTAL. The Si534x/7x/9x/83/84/88/89 products are designed to work with both normally-tested XTALs as well as activity dip-tested XTALs.

Please refer to relevant data sheets, reference manuals, and AN905 for XTAL drive circuit and layout recommendations.

2.  Recommended Oscillators

The most basic and precise timing reference is the XTAL. However, the XTAL alone will not sustain the oscillations to provide a stable clock. A driver circuit needs to be added to obtain a continuous and stable oscillation. This forms a basic XTAL oscillator (XO). XTAL oscillators come in many different versions based on their tunability and temperature stability.

Refer to Appendix B for information on XTAL oscillator specifications and how to choose the best XO for your application.

2.1   Recommended Stratum 3/3E OCXO/TCXOs

The table below is a list of low frequency Stratum 3 TCXOs and Stratum 3E OCXOs that have been approved for use with members of the Si534x/7x/8x/9x family. These devices, such as the Si5348, have a separate Reference Clock input distinct from the XA-XB inter- face.

Some of the part numbers in this table are custom generated for Silicon Labs. Part Family information is included in the table to enable searching through vendor websites. Users can also contact the vendor directly and ask for the specific part number listed.

Table 2.1.  Recommended Stratum 3/3E Oscillators

2.2  Recommended Stratum 3 High Frequency TCXOs

The table below is a list of high frequency Stratum 3 TCXOs which have been approved for use with the Si534x/8x/9x family in general when connected at the XA input. See the appropriate Reference Manual for the TCXO to XA input interface circuit.

Some of the part numbers in this table are custom generated for Silicon Labs. Part Family information is included in the table to enable searching through vendor websites. Users can also contact the vendor directly and ask for the specific part number listed.

Table 2.2.  Recommended Stratum 3/3E TCXOs

2.3  Recommended XOs

The table below is a list of XOs which have been approved for use with the Si534x/8x/9x family in general when connected at the XA input. See the appropriate Reference Manual for the XO to XA input interface circuit.

Some of the part numbers in this table are custom generated for Silicon Labs. Part Family information is included in the table to enable searching through vendor websites. Users can also contact the vendor directly and ask for the specific part number listed.

Table 2.3.  Recommende XOs

Recommended Crystal, TCXO, and OCXO Reference Manual for High-Performance Jitter Attenuators and Clock Generators

Appendix A—How to Select the Right XTAL for your Application

3.  Appendix A—How to Select the Right XTAL for your Application

Selecting a XTAL involves investigating the XTAL for its properties and performance. The purpose of this section is to enumerate the properties of the XTAL and how it affects the final performance. XTALs operate by the piezo-electric effect, so both the electrical and the mechanical aspects of the XTAL play a role in determining its suitability for the given purpose.

Data Sheet Electrical Specifications Frequency:

The nominal operating frequency of the XTAL is determined by the internal L-C resonance in the XTAL model, as discussed in the section below, XTAL Equivalent Model. XTALs can operate at either the fundamental frequency or at overtones of the fundamental. Fundamental XTALs generally have better jitter and phase noise performance.

Frequency Accuracy:

The construction and manufacturing process determines the accuracy and performance of the XTAL. These factors can be analyzed in terms of the variation they cause from the ideal operating point of the XTAL.

Frequency error is a cumulative value which is a combination of multiple factors. This number needs to be within the limit specified by the Si534x/7x/8x/9x to guarantee proper PLL operation and specified performance. Accuracy is represented in parts per million (ppm) or parts per billion (ppb).

ppm error = ((Actual frequency – ideal frequency) / ideal frequency) x 10⁶

ppm error = ((Actual frequency – ideal frequency) / ideal frequency) x 10⁹

XTAL Equivalent Model

A quartz XTAL can be modelled electrically as a series RLC in parallel with a capacitance indicating the connections as shown in the figure below.

Figure 3.1.  XTAL Symbol and its Equivalent Electrical Model