Introduction
The CLK63 is a high-performance clock generation integrated circuit developed for demanding digital systems that require precise timing and low jitter. It supplies multiple synchronized clock outputs from a single reference input, making it suitable for data communication backbones, real‑time processing platforms, and mixed‑signal embedded applications. Designed to meet the strict timing constraints of modern high‑speed interfaces, the CLK63 provides programmable frequency multiplication, fine phase adjustment, and comprehensive power‑saving features. The device is available in a compact 64‑pin leaded package that supports both board‑mount and socketed installations, and it is compatible with standard analog and digital signal conditioning techniques.
Clock generation is a critical function in many electronic systems. In telecommunications, for example, timing accuracy directly influences data integrity and error rates. Likewise, in high‑speed Ethernet and optical networking, clock distribution must maintain low phase noise and strict skew tolerances to preserve signal quality. The CLK63 addresses these challenges by integrating a sophisticated phase‑locked loop (PLL) with a fully programmable frequency synthesizer, enabling designers to tailor the clock characteristics to their specific application requirements. The chip’s versatility and compact footprint have made it a common choice for engineers working on next‑generation communication infrastructure, data acquisition systems, and advanced signal processing solutions.
History and Development
Industry Context
During the early 2000s, the expansion of broadband networks and the proliferation of high‑speed data links created a demand for cost‑effective, high‑precision clock sources. Traditional crystal oscillators and discrete PLL components were increasingly inadequate for meeting the stringent phase noise, jitter, and skew specifications imposed by emerging protocols such as 10 Gigabit Ethernet, 40 Gigabit Ethernet, and fiber‑optic transceivers. In response, several semiconductor vendors began developing integrated clock generators that combined multiple functions into a single silicon die.
Product Genesis
The CLK63 was first conceived by the engineering team at Clockworks Solutions in 2005. The company had a long history of producing reference clock and oscillator solutions for telecommunications equipment. The CLK63 was designed to fill a gap in the product line: a device that could generate up to 63 synchronized clock outputs while offering programmable frequency multiplication and phase control, all within a modest power envelope. After a series of prototype evaluations, the first commercial release occurred in 2007. Since then, the CLK63 has undergone several revisions to improve performance, broaden the input frequency range, and reduce power consumption.
Technical Overview
Device Class and Packaging
The CLK63 is classified as a mixed‑signal integrated circuit, combining analog PLL circuitry with digital control logic. It is available in a 64‑pin leaded package, typically a dual‑in-line or ball‑grid configuration, and supports both through‑hole and surface‑mount deployment. The package offers a maximum pin current rating of 20 mA per pin and a maximum operating temperature range of –40 °C to +85 °C. The device is also compliant with RoHS and REACH regulations, ensuring environmental safety.
Clock Generation Method
The core of the CLK63 is a charge‑pump PLL that locks to an external reference oscillator. The PLL includes a voltage‑controlled oscillator (VCO) with a tunable frequency range of 100 MHz to 3.5 GHz. An integrated phase detector monitors the phase difference between the VCO output and the reference, driving a loop filter that regulates the VCO. The loop bandwidth is programmable between 1 kHz and 50 kHz, allowing designers to balance stability with fast lock‑time.
Phase Noise and Jitter Characteristics
Under typical operating conditions, the CLK63 exhibits a phase noise of –80 dBc/Hz at 1 kHz offset and –100 dBc/Hz at 10 kHz offset for a 1 GHz output. The integrated timing jitter, measured as root‑mean‑square (RMS) over a 1 MHz bandwidth, is below 50 ps for the 1 GHz clock. These specifications enable the CLK63 to support 10‑Gigabit Ethernet (10GBASE‑SR) and 40‑Gigabit Ethernet (40GBASE‑SR) link layers, both of which require jitter budgets in the sub‑hundred‑picosecond range.
Power Consumption and Thermal Performance
The CLK63 consumes a typical 1.2 W of power when operating at full load (i.e., with all 63 outputs enabled and generating a 1 GHz clock). The device offers a power‑down mode that can reduce consumption to 200 mW by disabling unused output channels. The thermal design guide recommends a minimum heat‑sink area of 15 mm² for sustained operation at full load, with a target junction temperature below 70 °C. The chip’s thermal resistance from junction to ambient is 15 °C/W, allowing designers to maintain reliable operation in high‑density board configurations.
Architecture and Internal Structure
Phase‑Locked Loop Subsystem
The PLL subsystem comprises a 10‑stage charge‑pump phase detector, a second‑order loop filter, and a 2‑stage VCO. The phase detector uses a digital‑logic comparator with a resolution of 1.8° per LSB at the VCO frequency. The loop filter is implemented as a switched‑capacitor network, allowing programmable bandwidth settings through a simple I²C interface. The VCO uses a CMOS ring oscillator structure with 32 stages, each stage comprising a low‑loss inverter. This architecture provides low harmonic distortion and a wide tuning range.
Frequency Synthesizer
After the PLL locks, the synthesized frequency is routed to a programmable fractional‑N synthesizer. The fractional‑N module employs a digital word‑length counter and a low‑frequency oscillator (LFO) to modulate the division ratio at rates up to 20 MHz. This design allows precise tuning in increments of 1 Hz for output frequencies below 100 MHz, and sub‑Hertz resolution for higher frequencies. The fractional‑N loop is isolated from the main PLL to reduce spurious emissions.
Output Distribution Network
The CLK63 provides up to 63 identical clock outputs, each routed through a dedicated low‑skew buffer. The buffers are implemented as differential push‑pull outputs with a characteristic impedance of 50 Ω. The outputs support both single‑ended and differential signaling, allowing designers to select the most suitable interface for their system. The buffer’s drive strength is programmable from 2 mA to 6 mA per output, accommodating a wide range of load conditions.
Control Interface
Device configuration is performed via a 2‑wire serial interface compliant with the I²C standard. The I²C bus allows the host processor to set the reference frequency, output frequencies, phase offsets, and power‑down flags. The interface supports a maximum data rate of 1 MHz, sufficient for most real‑time reconfiguration scenarios. The internal firmware implements a simple command decoder that translates I²C writes into control register updates, with error checking enabled through parity bits.
Key Features and Capabilities
- Programmable frequency multiplication up to 3.5 GHz
- 63 independent clock outputs with low skew
- Fractional‑N synthesizer with sub‑Hertz resolution
- Integrated I²C control interface
- Low phase noise and jitter suitable for 10/40 GbE
- Power‑down mode to reduce consumption
- Robust thermal design for high‑density boards
- Differential and single‑ended output support
- Wide input reference frequency range (2 MHz–200 MHz)
- Low‑loss differential routing for high‑speed interfaces
Applications and Use Cases
Telecommunications
In telecom infrastructure, the CLK63 is frequently used as the core timing source for baseband processors and transceiver modules. Its low jitter and fine phase control ensure compliance with SONET/SDH timing specifications, which demand sub‑nanosecond skew between multiple data lanes. The chip’s ability to generate multiple synchronized clocks makes it ideal for multi‑lane serial interfaces such as XGMII and XPCS.
High‑Speed Ethernet
High‑speed Ethernet protocols, particularly 10GBASE‑SR, 25GBASE‑SR, and 40GBASE‑SR, require clock sources with stringent jitter budgets and tight phase alignment. The CLK63’s 1 GHz reference and sub‑100 ps jitter meet these requirements. Its differential outputs support the SFP+ and QSFP28 transceiver modules commonly deployed in data centers.
Optical Networking
Optical transport systems such as 100G PON and EPON benefit from the CLK63’s ability to generate low‑skew, low‑jitter clocks for modulator drivers and optical hybrids. The chip’s differential outputs can be directly interfaced with optical drivers that require 100 MHz to 1 GHz clock signals, reducing the need for external phase alignment circuitry.
Data Acquisition Systems
In high‑speed data acquisition, precise timing between analog-to-digital converters (ADCs) and digital signal processors (DSPs) is essential. The CLK63 can supply a synchronized clock to an array of ADCs, ensuring that sampled data streams remain phase‑aligned. The low skew and programmable offsets simplify the synchronization of multi‑channel capture boards.
Embedded Systems
Embedded platforms that integrate high‑speed communication interfaces, such as automotive Ethernet or industrial fieldbuses, often use the CLK63 as a single source for all timing signals. Its compact footprint and low power consumption align with the constraints of embedded board design, while its robust feature set supports a wide range of protocols.
Variants and Family Members
The CLK63 family has evolved through several iterations to address specific market needs. The base model, CLK63‑V1, offers 63 outputs with a maximum output frequency of 1 GHz. The CLK63‑V2 adds a second VCO to extend the maximum output frequency to 3.5 GHz, enabling 100 GbE applications. The CLK63‑V3 incorporates an on‑chip temperature sensor and automatic trim functions to maintain frequency stability over temperature excursions. A low‑power variant, CLK63‑LP, reduces static current to 250 mA and includes a power‑down register for each output, enabling selective disabling to lower consumption in idle states.
Design Guidelines
PCB Layout Considerations
Effective implementation of the CLK63 requires careful attention to signal integrity. The differential outputs should be routed as 90 Ω microstrip lines, matched in length to maintain skew below 5 ps. The reference input must be placed adjacent to the CLK63 package to minimize parasitic inductance. Ground planes should be continuous under the reference traces and output pads to suppress common‑mode noise.
Power Supply Design
The CLK63 draws 1.2 W from a single 3.3 V supply. Designers should use low‑ESR decoupling capacitors - 10 µF tantalum followed by 0.1 µF ceramic - placed directly adjacent to each VDD pin. The supply should be filtered with a common‑mode choke to prevent conducted EMI. The power‑down feature can be controlled through a pull‑down resistor network that sets the default state on reset.
Signal Integrity and Crosstalk
Due to the high density of outputs, differential pairs can be susceptible to crosstalk. Maintaining a separation of at least 2× the trace width between adjacent pairs mitigates this risk. The use of guard traces or differential pair routing with controlled impedance reduces the likelihood of inter‑channel interference. Simulations using 3‑D electromagnetic field solvers confirm that 5 mm trace spacing yields an inter‑channel crosstalk of less than –60 dB.
Testing and Validation
Functional testing of the CLK63 involves verifying lock time, output frequencies, and phase alignment. A phase‑locked loop test fixture can inject a 5 MHz reference and verify the 1 GHz output using a vector signal analyzer. Jitter is measured by a time‑interval analyzer with a 1 GHz clock source and a 1 MHz bandwidth. Temperature cycling tests demonstrate frequency drift within ±50 ppb over a 0–85 °C range. These tests confirm compliance with the device’s data sheet specifications.
Firmware and Software Support
The CLK63’s I²C interface is supported by a reference library that abstracts the register addresses into high‑level API functions. The library provides functions such as clk_set_reference(frequency), clk_set_output(index, frequency, phase), and clk_power_down(index, enable). It also includes a status polling routine that returns lock status and error flags. The software stack is available in both Linux and bare‑metal environments, with a kernel driver included for Linux distributions used in data‑center boards.
Future Outlook
As networking speeds continue to rise, the CLK63 family is positioned to remain relevant through incremental enhancements. Planned features include a 32‑bit frequency trimming register and a digital self‑calibration mode that compensates for process variations. Integration with an external FPGA may allow on‑board real‑time reconfiguration of output phases, making the CLK63 suitable for dynamic data‑center topologies that require rapid re‑routing of high‑speed lanes.
Conclusion
The CLK63 represents a powerful, all‑in‑one solution for generating synchronized, low‑jitter clock signals in modern high‑speed digital systems. Its robust architecture, comprehensive feature set, and proven performance make it a compelling choice for telecommunications, high‑speed Ethernet, optical networking, data acquisition, and embedded applications. By following the design guidelines and leveraging the available variants, engineers can integrate the CLK63 into their systems with confidence in reliability and timing precision.
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