Software compensation reduces the TCXO’s frequency change with temperature. An external 1 PPS reference provides frequency correction when available.
The internal oscillator supplies both the frequency output and a separate one pulse per second (1 PPS) output. When the external reference is interrupted, the last frequency correction is retained and both outputs continue. Temperature stability, acceleration sensitivity and aging options are selected for the operating environment.
LGT900 module shown with a 10 MHz label. Nominal frequency is factory configured. Not to scale.
Free-running temperature option±2.0 ppb
−40 to +85 °C 1 °C/minute in still air
Acceleration-sensitivity option0.01 ppb/g
Per axis Selected low-G configuration
Frequency accuracy in lock±0.5 ppb
At room temperature External 1 PPS reference
The available combinations of temperature stability, acceleration sensitivity and aging depend on the selected configuration.
Temperature, Vibration and Aging
Temperature, vibration and aging produce different changes in oscillator frequency. Temperature compensation reduces frequency variation as the module warms or cools. Low acceleration sensitivity reduces frequency modulation under vibration. Aging adds to the frequency error that accumulates with operating time.
Airborne and Navigation Systems
Temperature changes and vibration affect the local oscillator even when an external timing reference is available. Its temperature and aging performance also determine frequency stability during reference interruptions.
Radar and RF Systems
Vibration-induced frequency modulation produces spectral components around the oscillator output. Acceleration sensitivity and phase noise therefore affect the reference’s contribution to the RF system.
Laboratory and Test Equipment
Frequency accuracy, temperature stability and aging contribute to reference error between calibrations. The output waveform and load determine compatibility with the connected equipment.
Frequency Stability over Temperature
ERD’s MSAC software compensation reduces the TCXO’s frequency variation with temperature. The selected free-running temperature-stability limit continues to apply when the external 1 PPS reference is unavailable.
The plot shows measurements from five units. Each trace is centered on that unit’s measured midrange over −40 to +85 °C. This removes the calibration offset so that the plot shows frequency variation with temperature.
Frequency versus temperature for five measured units. The sweep extends approximately −55 to +90 °C; the ±2 ppb specification applies over −40 to +85 °C.View full-size plot ↗
Acceleration Sensitivity
Acceleration-sensitivity options range from 0.25 to 0.01 ppb/g per axis. For a given acceleration, lower sensitivity reduces the resulting frequency modulation. The spectral effect depends on the vibration at the mounted oscillator and its sensitivity as a function of vibration frequency.
Short-Term Frequency Stability
Typical Allan deviation is 1.5 × 10−11 at an averaging time of 10 seconds, measured after two hours of continuous operation at constant temperature in still air. This measurement describes short-term frequency stability under those conditions. Temperature variation, aging and locked frequency accuracy are specified separately.
Aging Measurements and Long-Term Projections +
Aging Performance
Daily aging options range from ±1.0 to ±0.30 ppb/day, measured after 30 days of continuous operation at 55 °C. Long-term options range from ±300 to ±100 ppb as 20-year projections, evaluated after seven days of continuous operation at 55 °C.
The plot shows eight 10 MHz units measured over 35.12 days at a 55 °C setpoint. Recorded temperature remained between 54.8 and 55.2 °C. These measurements characterize the sample over the test interval; the long-term values are projections.
Aging measurements from eight 10 MHz units, with 1,591 measurements per unit. Each trace is referenced to its first measurement. View full-size plot ↗
1 PPS Discipline and Holdover
The internal TCXO generates the frequency output and the separate 1 PPS output. The LGT900 compares the external 1 PPS reference with its internal timing and adjusts the oscillator frequency.
External 1 PPS reference
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LGT900
Frequency discipliningAveraged reference timing
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Internal TCXOMSAC compensation
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Frequency outputLVCMOS or sine wave
Oscillator-derived 1 PPS3.3 V LVCMOS
The internal oscillator supplies both outputs. The external 1 PPS reference provides the timing information used for frequency correction.
01
Operation with an External Reference
The LGT900 averages the external 1 PPS timing and corrects the internal oscillator. Locked frequency accuracy is ±0.5 ppb at room temperature. The absolute timing error of each 1 PPS edge is a separate quantity.
02
Holdover
When the external 1 PPS reference is unavailable, operation continues from the internal TCXO with the last frequency correction retained. Both outputs remain active. Frequency stability and the resulting timing drift depend on its temperature and aging performance.
03
Reference Reacquisition
When the external reference returns, frequency discipline resumes and the 1 PPS phase realigns by a step. The returning reference can therefore shift the second boundary.
Output and Configuration Options
The frequency output is available as a 50 Ω sine wave or LVCMOS. Nominal frequency is factory configured to the nearest 1 Hz. Temperature range, stability, acceleration sensitivity and aging are selected for the application.
15 pF specified load; 3.3 V high and 0.1 V low, typical. 45–55% duty cycle; 6 ns maximum rise/fall time (10–90%).
Output swing, duty cycle and rise/fall specifications apply at 10 MHz under the stated loads. Performance at other frequencies may vary. Frequencies above 80 MHz are available with LVCMOS output only.
Electrical Requirements
Nominal frequency, waveform, receiving load, supply voltage and external 1 PPS source.
Operating Conditions
Temperature at the module, mounted vibration and expected intervals without the external reference.
Configuration Selection
Provide the required limits or indicate “No preference” where ERD should select an option. ERD will confirm compatible options and the complete ordering code.
The following specifications cover the supply, timing interfaces and available temperature options. The datasheet includes the complete electrical tables, ordering codes and package dimensions.
Supply voltage
4.75–5.25 V; 5.00 V nominal
Input power
0.5 W maximum Steady state at +25 °C
Free-running calibration
±50 ppb at shipment
Temperature stability options
±25.0 to ±0.5 ppb Across the ordered range; 1 °C/minute in still air. Available limits depend on the selected range and configuration.
Operating range options
0 to +70 °C through −40 to +105 °C The ±2 ppb example is specified over −40 to +85 °C.
1 PPS input
3.3 V LVCMOS; rising edge 10 MΩ in parallel with 10 pF
1 PPS output
3.3 V LVCMOS; 45–55% duty cycle 10 MΩ in parallel with 10 pF load
Connections
Frequency output, serial in/out, 1 PPS in/out, lock indicator, supply and ground Leave the N/C pin floating.
LGT900 packages and pin connections. Not to scale.
Pin Connections and Package Dimensions
The datasheet includes the pin assignments, mechanical outline and complete electrical specifications.
Send the complete ordering code or describe the required frequency, waveform, load and operating conditions. Include the following information, with “No preference” for any option ERD should select.
Nominal frequency, waveform and receiving load
Temperature range and stability limit
Vibration environment and acceleration sensitivity
