TECHNICAL INFORMATION

Published in "AEI March 2006"
TCXOs From Daishinku Cover Size, Precision Requirements

 Mobile phones continue to evolve into advanced gadgets with manufacturers adding new functions one after another into the newest models. Meanwhile, users are requesting smaller and lighter mobile phones. A trade-off usually occurs between upgrading functions and miniaturization. To resolve this contradiction, designers of mobile phones are promoting the embedding of functions into ICs and requesting smaller devices that will step up flexibility in layout design.
 Daishinku Corp. has supplied temperature-compensated crystal oscillators (TCXOs) as key devices for the radio signal units of mobile communication terminals. The company has worked too on smaller TCXOs to address the requirements of the market. It has recently developed a small, 2520-size TCXO (DSA221SA series) as the reference frequency oscillator for the radio signal units of mobile communication terminals, and a high-precision, 3225-size TCXO (DSA321SD series) as the reference frequency oscillator for the GPS receivers that can be built in mobile phones.

Small Requirements

 Daishinku's DSA221SA series (Fig.1) is the reference frequency oscillator for mobile communication terminals. The DSA221SA has maximum outside dimensions of 2.5*2.0*0.9mm and a volume of 0.0045cc (a 45 percent reduction from the volume of the 3225-size TCXO). The new, 2520-size TCXO adopts a single-package structure to achieve miniaturization.
 The single-package TCXO requires smaller ICs than those used in TCXOs adopting other structures. The 2520-size TCXO was the result of the development of new small ICs. The frequency stability against temperature of the DSA221SA series is ±2.0*10-6/-30 deg.C to +85 deg.C (Table 1).

Outline of the DSA221SA
Fig.1: Outline of the DSA221SA

 

Table 1: Electrical characteristics of DSA221SA and DSB221SA

Model DSA221SA(VC-TCXO) / DSB221SA(TCXO)
Output frequency 13MHz/ 14.4MHz/ 19.2MHz/ 19.68MHz/ 26MHz
Frequency range 9.6MHzto40MHz
Supply voltage +2.8V(+2.4V±0.1V supported)
Current consumption +1.1 mA max. (F≤15MHz)
+1.3 mA max. (15 +1.5 mA max. (F>26MHz)
Output level 0.8Vp-p min.
Output load (10kΩ//10pF) ±10%
Frequency tolerance ±1.5×10-6  (After 2 reflows)
Frequency stability vs. temperature ±2.0×10-6/-30°Cto+85°C
Frequency stability vs. supply voltage ±0.2×10-6/  (+2.8V±0.2V)
Frequency stability vs. load variation ±0.2×10-6/  (10kΩ//10pF) ±10%
Frequency control sensitivity ±9×10-6to±1.5×10-6  Vcont=+1.5V±1V (GSM)
±5.5×10-6to±9.5×10-6  Vcont=+1.4V±1V (CDMA)
Aging ±1.0×10-6/year
Startup time 2.0msec max.
* The table lists only some of the standard specifications. For other specifications, contact Daishinku.

High-Precision Needs

 Meanwhile, the DSA321SD series is a high precision, 3225-size single-package TCXO (Fig.2) developed as the reference frequency oscillator for Global Positioning System (GPS) receivers and business-use wireless communication equipment. The DSA321SD series has maximum outside dimensions of 3.2*2.5*1.0mm and a volume of 0.008cc (a 60 percent reduction from the volume of a 5032-size TCXO). The frequency stability against temperature of the DSA321SD series is ±0.5*10-6/-40 deg.C to +85 deg.C (Fig.3).
 The DSA 321SD series aids in the miniaturization of GPS modules built in mobile communication products. It is suitable for equipment that receive position information notification from mobile communication terminals such as the E911 service in the United States (similar devices are appearing in Japan and Europe), telematics, and the position information notification equipment and car navigation units, the market for which is expected to expand.
 The following paragraphs discuss the technical features and background of the newly developed TCXOs.

Outline of the DSA321SD
Fig2: Outline of the DSA321SD
 
Temperature characteristics of the DSA321SD
Fig.3: Temperature characteristics of the DSA321SD

Single-Package Structure

 The single-package structure is the technology Daishinku introduced to its 5032-size and 3225-size products. Although the single-package structure requires high levels of technology and management in the manufacturing process, it offers advantages such as facilitating the low-profile designs of products and reducing the total assembly time.
 Mounting of ICs in the product employs a special flip-chip mounting technique developed for the single-package structure. Single-package modules are lead-free devices, eliminating the use of lead for joints and materials (Fig.4).

Single-package structure
 
Fig.4: Single-package structure

Development of Small IC

 Daishinku pursued and attained the IC miniaturization required to reduce the size of the TCXO modules. The IC for the TCXO could be miniaturized significantly without degradation in performance. The IC was miniaturized by an area ratio of 34 percent compared with conventional IC.

Improvement in Thermal Design

 Daishinku also improved the thermal design of TCXO to increase the freedom of designing the TCXO layout on circuit boards.
 When a TCXO is placed near a device, for instance a power amplifier that generates large heat, the temperature in the TCXO may change drastically, resulting in temporary fluctuation of the frequency oscillated by the TCXO. The fluctuation is due to a temperature compensation error that is the result of the difference between the temperature of the crystal blank in the ceramic package and the temperature detected by the temperature sensor on the chip. Daishinku has successfully reduced the fluctuation by adjusting the thermal resistance between the ceramic package and crystal blank to the thermal resistance between the ceramic package and IC. This will enable the TCXO to be placed near a heat-generating device (Fig.5).

Reducing temperature compensation error
 
Fig.5: Reducing temperature compensation error

Enhancement of Harmonic Performance

 To improve the freedom of designing the TCXO layout on circuit boards, Daishinku reduced the high harmonics included in the output signal, which adversely affect the radio performance (Fig.6). The high harmonics in the TCXO output signal can adversely affect the speech quality of the call received by mobile phone and the signal-receiving sensitivity of the GPS equipment. The high harmonics especially influence the devices and signal lines that handle low-level signals and limit the freedom of TCXO layout on circuit boards.

Reduction of harmonics
Fig.6: Reduction of harmonics

Daishinku reduced the high harmonics in the TCXO output signal in circuit level, allowing more freedom in designing the TCXO layout in the circuit board. Accordingly, equipment containing the TCXO can be designed smaller than before.

Support of Low-Voltage Operation
 Daishinku lowered the internal operating voltage of the ICs to support the lowering of the voltage of power supply. This improvement enabled the TCXO to operate with a supply voltage of +2.4V±0.1V. Lowering the operating voltage makes it possible to reduce the power consumption of the entire equipment containing the TCXO.

Eliminating Damp-proof Packaging

 Daishinku eliminated the need for damp-proof packaging for the TCXO to facilitate the handling of the device. Damp-proof packing is required for devices that use hygroscopic materials for example resin, for parts exposed to the air. With Daishinku's TCXO adopting single-package structure, hygroscopic materials and the need for damp-proof packing control were eliminated.
 The T_STD_033 standard of JEDEC define the levels of damp-proof packing control. The moisture sensitivity level (MSL) of Daishinku's TCXOs is “1”, which means damp-proof packing is not required. The MSL of TCXOs that do not employ the single-package structure is “3”, which requires damp-proof packing.

 

About This Article
 The author, Masaki Yamashita, works at Laboratory No.1 of Daishinku Corp.'s Central Laboratory.