Bomar Part Numbering Guide

Part Numbering Guide for Crystals

Part Numbering Guide for Oscillators


Crystal Oscillator

A timing device that consists of a crystal and an oscillation circuit, providing an output waveform at a specific reference frequency.

VCXO (Voltage Controlled Crystal Oscillator)

A kind of oscilltaor that has the output frequency change with a voltage change at a control pin of the oscillator.

TXCO (Temperature Compensated Crystal Oscillator)

A kind of oscillator that adjusts the frequency for temperature variation and commonly has an outside adjustment for calibration frequency periodically. This is compensate for the aging of the crystal over time.

OCXO (Oven Controlled Crystal Oscillator)

A kind of Oscillator that uses an oven to stabilize the frequency variation.

Nominal Frequency (or Center Frequency)

The specified reference frequency of the oscillator, typically specified in Megahertz and Kilohertz.

Frequency Stability

The amount of frequency deviation from center frequency associated with a set of operation conditions, express in parts per million (PPM). This condition includes: Operating Temperature Range, Supply Voltage and Output Load.

Frequency Tolerance

The permissible deviation, from the nominal frequency at the reference temperature (usually 25° C)

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Operating Temperature Range

Termperature range where specification characteristics are fulfilled. This needs to be specified carefully as it impacts cost.

Storage Temperature Range

Temperature rante where specification characteristics can be maintained for discharged state (no input of voltage, current, or power). Exposure to temperatures over this level may result in characteristic degradation or destruction.

Frequency Aging

Amount of frequency drift when operated under the specified conditions for a specified length of time.

Logic Levels

Defined as the Ouptut Voltage Logic High or "Logic 1" and the Output Voltage Logic Low or "Logic 0" Voltage "0" level (max.): +0.4VDC TTL, +0.5VDC HCMOS for Vdd=5VDC (Vdd: Supply Voltage) Voltage "1" level (min.): +2.5VDC TTL, +4.5VDC HCMOS for Vdd=5VDC

Tri-State Output

An oscillator with this feature allows the output to be placed in to a high impedance state. This feature is activated by the application of a logic control voltage to pin 1 of the oscillator.

Supply Voltage (or Input Voltage)

The DC input voltage necessary for oscillator operation. Currently 5VDC is common used, with 3.3VDC being used in portable equipment.

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Supply Current (or Input Current)

The amount of current consumption by an oscillator form the power supply, typically specified in milliamps.

Rise/Fall Time

The Rise Time is defined as the transition time from an output logic low to an output logic high. The Fall Time is defined as the transition time from an output logic high to an output logic low.

Duty Cycle (or Symmetry)

The measure of output waveform uniformity. The ratio of full and half cycles. For CMOS loading duty is rated at 1/2 VDC, and for TTL loading at 1.4 VDC.

Pull Range of VCXO

The frequency range from the nominal frequency over which the ouput frequency ofa VCXO under reference conditions can be changed by means of an exgternal DC control voltage, expressed in PPM.

VCXO Linearity

Defined as the % variation in output frequency versus control voltage from a best fit straight line.

Start-up Time

The specific time from oscillator power-up to the time the oscillator reaches steady oscillation.

Output Load

The capacity of oscillator to drive other devices or the fan out. TTL devices are specified in number of gates that can be driven. CMOS outputs are specified in pF.