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KYOCERA Produces Industry's First Crystal Unit with Temperature Sensor Allowing Highly Precise Temperature Compensation, Compatible with Qualcomm Chipsets

June 6, 2011
Kyocera Corporation (President: Tetsuo Kuba) announced that it has produced the industry's first crystal unit with a thermistor, a temperature sensing component. This product named “CT2520DB” is an AT cut type crystal unit with a size of 2.5 x 2.0mm. Kyocera started providing samples in March.

Mobile handsets such as cellular phones require crystal devices to produce the reference signal for stable communication. In these systems, temperature compensation of the crystal unit is quite important to minimize frequency change under a wide operating temperature range.

These days crystal units are coming to be used in many designs replacing TCXOs, a popularly used device currently, in an increasing number of smartphones, 3G and CDMA handsets; and temperature sensors are required to be placed as close as possible to the crystal unit for high precision temperature compensation.

“CT2520DB” is a crystal unit with a temperature sensor to realize high precision temperature compensation which is required in the trend of replacement of the TCXO with a crystal unit, especially in handsets using Qualcomm's chipsets.

The size of this product is 2.5 x 2.0mm, the frequency is 19.2MHz, and the operating temperature range is -30 to +105 degrees Celsius which fits the specifications for wireless communication. In order to compensate frequency change caused by thermal transients, the thermistor is placed as close as possible to the crystal unit. Not only are they located close together, but delay of temperature change between the crystal unit and thermistor is minimized by placing these components on each side of a ceramic package.

The new product was created by KYOCERA Kinseki Corporation, a wholly-owned subsidiary of Kyocera engaged in the development and manufacturing of crystal devices.


Photo: Kyocera CT2520 crystal unit with built-in thermistor (0.5mm increments shown)
Kyocera CT2520 crystal unit with built-in thermistor (0.5mm increments shown)


Specifications

Parameters

Specifications

Frequency

19.2MHz

Overtone Order

Fundamental

Frequency Tolerance (25 °C)

+/-10 – +/-50 ppm

Operating Temperature Range

-30 – +105°C

Frequency Temperature Characteristics
(-30 – +85°C)

+/-10 – +/-50 ppm
(Deviation from the frequency at 25°C)

Motional Series Resistance

80 Ω Max.

Drive Level

100uW Max.

Load Capacitance

6pF, 7pF, 8pF, 10pF, 12pF and others

Thermistor (Resistance)(25 °C)

100k Ω and others

Thermistor (B Constant)(25 °C – 50 °C)

4250K and others


Features

1. Utilization of temperature data in the vicinity of crystal unit
“CT2520DB” contains a thermistor in the same package with crystal unit. In the RF circuit of a cellular phone, frequency change caused by peripheral temperature is compensated by using temperature data sensed by a thermistor connected to the RF circuit. However, if the thermistor is not located near the crystal unit, or the circuit board shrinks due to further system integration, it is necessary to optimize the thermal transient response and thermal coupling between the thermistor and the crystal unit. The “CT2520DB” with the thermally coupled thermistor and crystal unit in conjunction with software developed by Qualcomm provide the ability to achieve state of the art performance in these high thermal transient and/or small form factor designs.

2. Excellent temperature tracking
This product has a ceramic wall in the middle, and the crystal unit is place on the top of the wall, with the thermistor underneath the wall. This structure characterizes excellent temperature tracking of the crystal unit and thermistor since the heat reaches these components almost simultaneously. As a result, it is possible to compensate temperature with higher precision compared to circuits which have the crystal unit and thermistor placed apart.

3. Reduction of assembly space
Since this product has a crystal unit and thermistor in the same package, it reduces assembly space of the thermistor and peripheral routing, compared to the conventional design with these components placed apart, and contributes to the miniaturization of handsets.

4. High reliability
The crystal unit and thermistor are placed in two different cavities in this product, the thermistor and gas from conductive adhesive to connect do not affect crystal unit, and the product exhibits as high reliability as conventional crystal units.

5. Shield structure
The metal lid has shield effect by connecting the lid and one termination of the thermistor by internal via holes to make a ground. Thus, oscillation frequency shall not be affected by external ground such as cases.

6. Environmental compliance
Lead-free, compliant with the RoHS Directive and REACH regulation.

Qualcomm is a registered trademark of Qualcomm Incorporated.