Comparison between real-time clock module and discrete components of real-time clock

【Features of Epson Real Time Clock Module】

The real-time clock module is a product that packages a 32.768kHz crystal unit and a real-time clock chip together, with oscillation circuit, clock function, calendar function, and alarm function. The quartz crystal unit and real-time clock chip used in the real-time clock module are independently developed and produced by Epson. Therefore, it is possible to stably supply quartz crystal units that are most suitable for high-precision real-time clock modules, as well as real-time clock chips that drive the oscillation unit under optimal conditions. Moreover, the application of Epson semiconductor technology started with the world's first practical quartz electronic watch, and has also been used for the Olympic formula timing system and the heart control of Seiko high-end watches represented by "Grand Seiko". These semiconductor technologies used for controlling chips, combined with outstanding low-power, high stability quartz oscillation technology, form the foundation of high-quality real-time clock modules.

As mentioned above, we achieve optimal matching and maximize the strengths of both parties through independently developed quartz crystal units and real-time clock chips, thereby providing customers with high-performance products.

The following text explains the features of our company's real-time clock module.

[One feature: Clock accuracy has been adjusted]

Epson's real-time clock module is built with 32.768kHz crystal unit and real-time clock chip, which adopts an integrated structure and is provided to customers after the frequency accuracy is adjusted before leaving the factory. Therefore, customers no longer need to provide additional components, which can reduce the number of components used on the customer's substrate.

If discrete components are used, the oscillation frequency will be affected by the stray capacitance of the substrate conductive pattern, the internal capacitance of the chip, and the deviation of crystal units. Therefore, customers must invest effort in precision design to compensate for frequency deviations. Moreover, customers also need to consider the necessary evaluation items when using discrete component structures as shown in Figure 1, such as clock accuracy adjustment and oscillation stability of oscillation circuits.

Figure 2 shows the deviation phenomenon generated when using discrete component products.

The frequency tolerance accuracy of tuning fork type quartz crystal units commonly sold in the market is+20x10. Due to the frequency adjustment of each product during the production process of crystal units,. So the deviation is concentrated in the data center. The deviation between chips is about+10x10 ", and the data distribution in different centers varies depending on the production batch number.

The discrete component products composed of the above two components require external capacitors and wiring on the substrate for frequency adjustment. The deviation after considering these factors is shown in Figure 2.

    In contrast, Epson's real-time clock module uses our company's self-designed and produced 32.768kHz crystal unit and real-time clock chip, which can be adjusted to absorb chip deviations (as shown in Figure 3), and does not require external capacitors and wiring for frequency adjustment when using discrete components. Therefore, compared with the discrete component method, the comprehensive deviation can be reduced to 2/3. Moreover, adopting a modular approach can reduce the workload of customers for circuit evaluation (matching evaluation) component evaluation, contributing to shortening the development cycle.

Epson has also launched digital real-time clock modules "RX4803SA/LC" and "RX8803SA/LC" with built-in TCXO, which can provide higher clock accuracy. Please refer to the "Features of Built in TCXO Digital Real time Clock Module" for details。

【Feature 2: High reliability】

The usual real-time clock operates with extremely weak current, and the oscillation circuit around the oscillation unit is susceptible to external environmental influences. When using discrete components, the oscillation circuit part that is easily affected by the external environment is exposed on the substrate and is susceptible to condensation and other effects.

As shown in Figure 4, when the oscillation circuit is affected by condensation or other factors, the oscillation will become unstable (2) or stop (3) and cannot continue timing. Therefore, when using discrete components, it is necessary to apply coating agents to avoid condensation and solve the above problems.

In contrast, the oscillation circuit of Epson's real-time clock module is not exposed and is not easily affected by condensation. Therefore, there is no need to apply plating agents, which can maintain the high reliability of the product.

【Comparison between modules using crystal units and MEMS modules】

Based on the market demand for maintaining real-time clocks with extremely weak currents, low-frequency clocks used for timing generally use tuning fork type quartz crystal units. For this reason, most customers choose 32.768kHz crystal units, but in recent years, integrated high-precision modules with built-in MEMS have gradually emerged (clock accuracy: -40 to+85 ℃, month difference of 13 seconds). Here, we compare modules using crystal units with MEMS modules.

【Regarding current consumption】

Compared with tuning fork type crystal units, MEMS module products are difficult to achieve lower frequencies. So, its oscillation frequency is set to around a few hundred kilohertz, which is relatively easy to manufacture, and the target frequency for clocks is achieved through frequency division.

Figure 5 shows the current consumption of Epson module products and MEMS module products.

The current of Epson products is 0.75uA, while that of MEMS products is more than 2.5 times that of 2uA, indicating that MEMS products do not have an advantage in long-term backup in market demand.

For this reason, MEMS products require large capacity batteries, and customers may face problems such as rising costs and difficulty in miniaturizing products.

Figure 5: Comparison of current consumption between MEMS module products and Epson products

【Regarding the 32.768kHz frequency output function】

The 32.768kHz frequency output by the tuning fork type crystal unit for clocks is also a target for some customers, and the output frequency also needs to achieve high precision. Figure 6 shows the temperature characteristic curves of the 32.768kHz output frequency of Epson products and MEMS products.

Figure 6: Comparison of 32.768kHz output frequency temperature characteristics between Epson products and MEMS products

In the temperature range of -40 to+85 ℃, the frequency output accuracy of Epson products can reach a high accuracy of ± 5 × 10-6 (equivalent to a monthly difference of 13 seconds), while MEMS products cannot compensate for the temperature of the output frequency, resulting in an output accuracy of ± 0.2% (equivalent to a monthly difference of 86 minutes) within the same temperature range, causing significant deviation. Therefore, the frequency output of MEMS products cannot be used for clocks.

【Regarding the Clock Accuracy Adjustment Function】

Epson has also launched products equipped with logic adjustment methods (* 3) in response to the need for further adjustment of clock accuracy after being installed in the product. This function can push forward or delay the built-in clock time of the real-time clock. It can advance or delay the clock/clock accuracy made by an internal quartz oscillator circuit with a frequency of 32.768 kHz to ± 189.1 × 10-6 in units of ± 3.05 × 10-6, thereby achieving high-precision time clock.

(* 3) Models equipped with logic adjustment mode: RX6110SA RX-8035SA/LC、RX-4035SA/LC、RX-8025SA/NB、RX-4045SA/NB、RTC-7301SF/DG 。

In summary, Epson provides high-precision and low-power real-time clock module products to the market through its production technology of tuning fork type quartz crystal units with low power consumption advantages and compensation circuit technology for frequency and temperature characteristics. Compared with discrete components or the same module products, its overall performance is also very superior. Moreover, our products have adjusted the frequency precision before leaving the factory, which is provided to customers on the basis of ensuring the precision, so there is no need to adjust the frequency when using, making great contributions to customers to improve design efficiency and product quality.