SpectraLinear
Timing Industry
Timing products can be classified under two basic categories. Clock generators are the category of timing devices that provide the clock source. They can be as simple as a crystal oscillator, or it can be a PLL based frequency synthesizer, or a stand-alone EMI reduction chip or a large scale fully integrated system clock that provides all of the timing requirements of an electronic system.
The other category of timing products are clock buffers which are the type of timing devices that distribute (rather than generating) an incoming clock signal. There are a wide variety of buffer products from simple versions without a PLL to versions with PLL to more complex programmable versions with skew adjustment, control and other features.
Overall size of the timing industry including all categories of oscillators approaches 3 billion dollars and the integrated timing device segment of the market is approximately 1.3 billion dollars.
A breakdown of product categories that address the overall timing market are described in more detail below.
Clock Generators
SpectraLinear as a broad base diversified supplier of timing products intends to participate in almost all of the following categories with few exceptions that are highlighted
• Resonators and Oscillators
The most primitive form of an oscillator is ceramic resonators which are piezoelectric devices. These ceramic devices are designed to oscillate at a frequency dependent on the property of materials they are manufactured from. Due to the nature of the materials and the control of the manufacturing processes, these types of oscillators are at the low end of the performance spectrum. They have relatively low Q (quality) factor and lack frequency and temperature stability. Therefore, they are used in low cost applications where performance is not critical.
Crystals are by far the most commonly used resonant element. They have high accuracy and they exhibit good frequency stability due to their high Q factor. They are designed to oscillate at a frequency dependent on the cut which determines the tune of the crystal.
All these resonant elements need support circuitry (oscillator circuitry) that consists of excitation, detection and amplification circuitry. Crystals with oscillating circuitry in one package is called a crystal oscillator. The output of the crystal oscillator is a square wave, a clock, whose frequency is fixed to the resonant frequency of the crystal. At this time, the company is not pursuing any of this low end oscillator market.
• Programmable Oscillators
A derivative of a crystal oscillator is a programmable oscillator which consists of a crystal and a clock generator. Clock generators have an integrated oscillator and a PLL circuit. Oscillator generates the fixed frequency from the crystal and feeds it into the PLL which is configured to generate the desired frequency from the fixed input frequency.
These types of basic programmable oscillators have great synergy and fall in line with the core competency of the company. It is our intention to offer a family of products to address this market place.
There are few companies involved in research to come up with a viable resonating element that can replace the crystal and offer an alternative that can be integrated with the oscillator circuitry and hence, eliminate the need for a discrete crystal. Some of these activities involve SAW, MEM and LC structures and are yet to be technically and commercially proven as alternatives for quartz crystal oscillators. It is the intent of SpectraLinear to engage with these types of companies at a later stage and form a strategic partnership.
In addition to these types of oscillators there are monolithic RC relaxation oscillators that generate a clock output. These types of oscillators have the advantage of not requiring an external resonating element but lack accuracy and stability and hence, can only be used in limited applications. At this time SpectraLinear has no intention to pursue these types of products but may do so in the future.
• Frequency Timing Generators
Clock generators are also known as frequency synthesizers or frequency timing generators and generate multiple outputs with a wide range of frequencies. They can accept a clock input or a crystal input as they have internal oscillator circuitry that can accommodate a wide range of crystals. Furthermore, the input can be a wide range of frequencies, and the output frequency can be an entirely different frequency in relation to the input, but yet with a high degree of accuracy and stability. Furthermore, the user can set and configure the number of outputs and associated frequencies.
• EMI Reduction/Spread Spectrum Clock Generators
These are very similar to basic clock generators but also have the spread spectrum feature that provides a spread clock output(s). SSCG (spread spectrum clock generator) is a frequency modulation technique used to reduce EMI (electro- magnetic interference) emission levels to comply with the regulation standards .
The SSCG technique modulates the clock frequency into a tightly controlled broader frequency band to reduce the peak amplitude of the emissions (fundamental and harmonics both) and thus reduce EMI.
These types of clock generators are capable of providing multiple spread outputs as well as non spread outputs of different frequencies.
• System Clocks
System clocks are the highly integrated large scale clocks that generate and distribute all the major timing requirements of a complex electronic system. PC clocks that fall under this category provide all the necessary timing signals of the motherboard and fulfill all the clocking requirements of the CPU, chip sets, and the peripherals. There are also application specific clocks to address advance digital consumer markets such as set-top boxes, HDTV’s, DSC’s, DMC’s, video games, etc. Some of these solutions can be customer specific to accommodate a specific customer architecture within the application group.
Buffers
Buffers are used to take an input clock of sorts and provide multiple copies of outputs, multiply and divide clock frequencies. Buffers are also capable of moving clock edges backwards and forward (adjusting the skew), vary the strength of the outputs (adjusting the slew rate and drive), and offer a wide variety of input/output voltage standards (CMOS, LVDS, PECL, etc.).
In general, in clock buffers the output waveform follows the input waveform. The input clock propagates through the circuitry of the buffer chip and is driven by the output circuitry to provide multiple print outs of the input of the clock. Some of these buffers are also called fan-out buffers as one brings in a clock input and fans it out to multiple outputs and drive multiple loads. In synchronous system designs, multiple synchronous outputs are often needed to drive a variety of components, and buffers are used to meet this pervasive need.
• Fan-Out Buffers
In general buffers without a PLL are called Fan-Out Buffers. In these types of buffers the input clock is propagated through the device and multiple outputs that are synchronous to the input clock are provided. The outputs follow directly the input signal with a propagation delay that is a function of the design techniques and process technology utilized. With careful input/output circuitry considerations, one can carefully watch the rise/fall times and output to output slew can be minimized. However, as the output waveform is a replica of the input clock at best with a propagation delay, and deficiencies of the input clock such as duty cycle is replicated in the outputs as well.
• Zero Delay Buffers
The second type of buffers are PLL Buffers. As the name implies they have an internal PLL and hence have the ability to add more features and make up for some of the shortcomings of the Fan-Out Buffers.
PLL based buffers have the capability to multiply clock frequencies, correct clock duty cycles ability to provide phase shifts to compensate for loading conditions and get negligible propagation delays due to circuit techniques utilized. Outputs can be selectively inverted, multiplied or divided and adjusted for skew. Furthermore, by clever circuit design, one can add/subtract skew, i.e., lead/lag the output waveform transitioning with respect to the input and hence can come up with programmable skew buffers.
Note that buffers whether it is a Zero Delay Buffer or a Fan-Out Buffer have the capability to offer a wide variety of input/output protocols. Some of these are HSTL, LVTTL/LVCMOS, PECL, LVPECL, LVDS, as well as regular single ended CMOS structures.
