Crystal unit with a thermistor to replace
TCXO in mobile handsets
Kyocera Corporation has produced crystal unit with a thermistor.
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.
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.
Source: Kyocera