10MHz to 51.84MHz TCXO

8

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DS4026

TEMP

SENSOR

GND

GNDOSC

GNDD

FOUT

GNDA

SCL

SDA

INTERFACE

CONTROLLER

DAC

CMOS

BUFFER

A/D

GND

EEPROM

ARRAY

GND

GND

Figure 2. Functional Diagram

Detailed Description

The DS4026 is a TCXO capable of operating at 3.3V

±5%, and it allows digital tuning of the fundamental fre-

quency. The device is calibrated in the factory to

achieve an accuracy of ±1ppm over the industrial tem-

perature range, and its minimum pullability is ±8ppm

with a typical resolution of 1ppb (typ) per LSB.

The DS4026 contains the following blocks:

• Oscillator block with variable capacitor for compen-

sation

• Output driver block

• Temperature sensor

• Controller to read the temperature, control lookup

table, and adjust the DAC input

• DAC output to adjust the capacitive load

The oscillator block consists of an amplifier and variable

capacitor in a Pierce crystal oscillator with a crystal res-

onator of fundamental mode. The oscillator amplifier is a

single transistor amplifier and its transconductance is

temperature compensated. The variable capacitor is

adjusted by the DAC to provide temperature compensa-

tion. With the FTUNEH and FTUNEL registers, a minimum

pullability of ±8ppm (±5ppm for 10MHz) is achieved with

a typical resolution of 1ppb (typ) per LSB.