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 Published in "AEI June 2007"

Daishinku's Latest TCXOs Cater to Mobile Phone, GPS Markets

Development of temperature-compensated crystal oscillators focuses on package size reduction and high frequency stability over wide temperature ranges.

 Mobile phones are undisputably a major application area for temperature-compensated crystal oscillators (TCXOs) . The transition to third generation systems has seen mobile phones come to maturity with a plethora of new applications contained in slim, light  weight designs. Amid this trend, significant growth in the employment of Global Positioning System (GPS) inside mobile phones is expected. GPS was pioneered in the United States when the U.S. military began using it in 1995, but from very early on the up take rate in the consumer sector has been very fast. In Japan, GPS is widely used in car navigation systems and recently mobile phones equipped with GPS are fast becoming popular . Furthermore, the market for personal navigation devices (PND) within Europe and the United States has also grown rapidly.
 Daishinku Corporation’s newly developed TCXOs meet the requirements for a majority of these mobile phone, PND and GPS applications.

 

Size Reduction

 To keep up with the trend in product miniaturization there is a big demand for small and lightweight TCXOs. Until recently 3225 size has been widely used for mobile phone applications but transfer to 2520 size is now picking up speed. Migration from the 5032 size to the 3225 size is also accelerating for GPS related equipment.
 In this relation, Daishinku has been a leader in the reduction of electronic circuits to IC chip form, which is key to TCXO miniaturization. The progress of the company’s efforts toward TCXO miniaturization is explained in Fig. 1.
 Daishinku’s first TCXO featuring IC chip technology was released in 1997 and was a 9070-size package. Today, the smallest TCXO in its product line up is an incredibly small 2520-size package. That is just one-thirtieth the size of the original 9070 package.
 Daishinku products developed after the 5032 size display a single-package structure (See Fig. 2), which has significantly advanced the development of the company’s low-profile and low-cost products. The single-package structure requires manufacturing technology with very high technological and management standards and offers several big advantages including reduced lead time.
 The 2520-sized TCXO, DSA221SA series, now in mass production, has a maximum size of 2.5 × 2.0 ×0.9mm with a volume of 0.0045cc. This TCXO has been developed as a reference oscillator for mobile communications equipment. The single-package structure is key to its low profile (see Fig. 3 for dimensions) and it offers a frequency stability of ±2.0 × 10-6 over a -30°C to +85°C temperature range.

Fig.1

Fig.2

Fig.3

Designed for High-Accuracy

  With regards to GPS related equipment, the performance of TCXO has greatly improved the basic performance of GPS receivers, including reducing signal acquisition time after power up, better reception sensitivity and positioning accuracy. In order to achieve this, TCXOs for GPS applications must maintain high frequency accuracy over a wide-temperature range. The temperature surrounding a TCXO in a GPS receiver changes dynamically due to heating up of devices. Large fluctuations in TCXO frequency associated with such changes in temperature will be manifested through degradations of reception sensitivity and positioning accuracy. Therefore, in addition to frequency temperature characteristics, the frequency slope or the amount of change in frequency per unit temperature has been defined as a specification for TCXOs to be used for GPS. Normally, TCXOs with frequency stability of ±0.5 × 10-6  over a -30°C to +85°C temperature range and temperature slope of ±0.1 ×10-6/°C are used for GPS.
 Today, Daishinku is mass-producing DSB321SD with an extended operating temperature range of -40°C to +85°C, which takes into consideration in-car equipment applications such as telematics. An example of the temperature characteristics is shown in Fig. 4.

Fig.4

Meeting Low Voltage Needs

 Daishinku has developed the DSB321SE TCXO, which can operate at a low voltage of +1.8V (operating between +1.7V and +3.0V). The lower limit of operation for conventional TCXOs is +2.4V, operating between +2.3V and +5.5V, however Daishinku has managed to lower the operating voltage down to +1.8V in one push. The DSB321SE has been developed with next generation GPS in mind. The development of ICs used in GPS is being advanced purposefully with an inclination towards miniaturization, low current consumption, and low voltage operation, targeting mobile phone and PND markets.
 In the future, most ICs used in a GPS receiver module will operate at +1.8V.  Reducing the operating voltage of TCXOs to +1.8V will allow all devices in a GPS receiver module to operate with the same +1.8V oltage. This will in turn make it possible to further reduce the size and current consumption of a receiver.
 The external appearance of DSB321SE is shown in Fig. 5 while its’ electrical characteristics are given in Table 1.  Working in conjunction with several GPS IC manufacturers, Daishinku aims at reducing the cost of DSB321SE by easing the specification of the frequency stability vs. temperature values. An example of the temperature characteristics is shown in Fig. 6. These characteristics have been realized on a circuit equal to a temperature-compensated circuit designed for mobile communications equipment. The DSB321SE is constructed using the characteristic Daishinku single package method (also lead free and RoHS compliant) and is aggressively priced.

Fig.5

Table1

Fig.6

Future Development

  Daishinku is pioneering the development of TCXOs to serve the mobile phone and GPS markets. Observing the market, the company can see the necessity to continuously re-assess its designs to meet market demands. For example, further miniaturization is a necessity. It will also be necessary to develop TCXOs with high-frequency accuracy that can cope with the dynamic changes in temperature that occur as a result of miniaturization. Furthermore, regarding low voltage products, the company needs to think about the development of solutions for the general mobile telecoms market. In this way Daishinku will continue to study market trends and strive to produce solutions that timely meet customer demands.

 About This Article

 The author, Masaki Yamashita,works in Section 1 of Central Laboratory, Daishinku Corp.