New knowledge of low-frequency oscillation circuit

catalogue

1. Market trends in electronic device products

2. The trend of changes in tuning fork crystal units and semiconductor process technology

3. The impact of miniaturization on characteristics and its countermeasures

3-1.  The oscillation stability caused by the increase of CI value (Crystal Impedance)

decline

3-2.  Deviation of oscillation frequency

3-3.  Oscillation fault caused by low voltage of microcomputer (MPU)

3-4.  crystal oscillator 

4. Introduction to Epson Toyocom's overall solution for kHz frequency band

4-1.  Tuning fork type crystal unit

(1) Product lineup of tuning fork type crystal units

4-2.  32.768 kHz oscillator

(1) Product lineup of 32.768 kHz crystal oscillators

1. Market trends in electronic device products

In recent years, with the increasing awareness of reducing environmental load, it is possible to maintain the high performance of electronic equipment products while also utilizing the small size of equipment and instruments The market demand for reducing raw materials and completely lowering power consumption through standardization is increasing. The market changes for electronic components are also similar, and crystal components used as reference clocks also require small size, low power consumption, high precision, and high reliability. This is not simply a matter of reducing the size of components, reducing size means the emergence of new issues and making existing ones more prominent.

Table 1 summarizes the main requirements for crystal units (tuning fork type crystal units) in the kHz frequency range for each major application. As shown in the table, tuning fork Type crystal units are mainly used for machine clocks, microcomputer sub clocks, and timing, and are widely used as essential components in various applications. From the table, it can be seen that there is a growing trend in the demand for small size, low power consumption, high precision, and high reliability in any market.

2. The trend of changes in tuning fork crystal units and semiconductor process technology

Figure 1 shows the trend of changes in the size of tuning fork type crystal units. From the past 20 years, it can be seen that the volume has shrunk from about 150 mm3 to about 1.5 mm3, sharply decreasing to the initial 1/100, and miniaturization is constantly advancing. We believe that in the future, research and development will also move towards miniaturization.

Figure 2 shows the trend of refinement in the design rules of low-power microcomputers (MPUs) with built-in oscillation circuits. The previous design rule was 0.2 μ m to 0.3 μ m, and the power supply voltage VDD was usually used to drive at 1.8 V to 3.0 V. But in recent years, with the progress of miniaturization and low voltage, it has leaped into the field of 0.1 μ m to 0.15 μ m and VDD=1.5 V to 1.8 V drive.

In addition, the power consumption requirement level during standby has also decreased from around 0.3 μ W in the past to 0.1-0.2 μ W in recent years. We believe that the refinement of design rules for cost reduction and the low voltage driving caused by power consumption reduction are the expected trends of the times that will not stagnate.

Due to the changing trends in tuning fork crystal units and semiconductor production technology mentioned above, our company's technical support team has received the following:

Multiple fault cases:

·The deterioration of oscillation stability is caused by the increase in CI value of the tuning fork type crystal oscillation unit.

·The increase in frequency sensitivity of the tuning fork type crystal oscillation unit causes a shift in oscillation frequency.

·Due to the refinement of semiconductor design rules and low voltage, the performance of anti power noise is reduced or oscillation margin is caused

Insufficient allowance, unable to obtain stable oscillation.

In the next chapter, we will explain the unique considerations of tuning fork crystal units caused by miniaturization and low voltage.

3. The impact of miniaturization on characteristics and its countermeasures

3-1.  The decrease in oscillation stability caused by the increase in CI value (Crystal Impedance)

If the resonant state of the crystal unit is replaced with an electrical circuit, the equivalent circuit of the crystal oscillation unit shown in Figure 3 can be obtained, and the CI value is equivalent to R1 of the equivalent circuit. When miniaturizing crystal oscillation units, the CI value usually increases. At this point, the impact of the CI value of the crystal oscillation unit on the oscillation circuit and its countermeasures are as follows.

[Impact]

When the CI value is high, the starting or stopping voltage will increase. Even if the voltage is increased, it will be difficult to start oscillating, and if the voltage drops slightly, the oscillation will become unstable

The phenomenon of stabilizing or stopping oscillation.

Moreover, the CI value is the equivalent impedance of the resonant frequency in a single crystal oscillator unit, which affects the instability or non oscillation of the oscillation One of the important parameters for determining oscillation margin.

Figure 4 Inspection method for oscillation margin

[Countermeasure]

Firstly, it is necessary to ensure that the oscillation margin for measuring whether the oscillation circuit can oscillate stably is above 5-10. This oscillation margin is available The negative impedance (CI) of the oscillation circuit in Figure 4 is represented by the maximum value of the equivalent series impedance (r) of the crystal oscillation unit.

When the oscillation margin is insufficient, faults such as delayed oscillation time or increased oscillation voltage as described above will occur. Moreover, when the oscillation margin is clear When insufficient, the oscillation will enter an unstable or non oscillating state.

In order to improve the oscillation margin, the following two methods are more effective: ① The method of improving negative impedance is usually more effective. According to the relationship between the power consumption and negative impedance of the oscillation circuit shown in Figure 5, the method of increasing the oscillation current can be used to solve this problem, but this method has the disadvantage of increasing power consumption..

② The use of quartz crystals with lower CI values can also improve the oscillation margin, but as mentioned above, the miniaturization of crystal oscillation units usually leads to a decrease in CI

The value increases.

Although miniaturization and oscillation stability are opposed, our company uses "QMEMS" technology and adopts a design that is both small and can suppress CI values. Our company has launched a diverse lineup of crystal oscillation units with various specifications and sizes based on customer needs, which can provide you with the best system components and support the high design quality of our esteemed customers.

Figure 5: Relationship between Current and Negative Impedance in the Oscillatory Circuit

3-2.  Deviation of oscillation frequency

With the miniaturization of oscillator size, frequency sensitivity will increase. When installed on the product substrate, the oscillation frequency may deviate from the expected value. The following says Identify its impact and countermeasures.

[Impact]

The frequency of the crystal oscillation unit varies with the load capacitance of the oscillation circuit. This change is called "frequency and load capacitance characteristics". The load capacitance is as follows:

1) As shown, it is determined by the capacitance value and stray capacitance of the oscillating circuit. The frequency and load capacitance characteristics are shown in Figure 6, depending on the specifications of the oscillator Inches but different. The accuracy of frequency increases with the miniaturization of oscillator size, and the frequency sensitivity of capacitance per 1 pF will become higher (the slope of the curve becomes sharp), so the frequency is easily affected by the uneven stray capacitance of each substrate. The offset of the oscillation frequency increases.

The countermeasures for crystal oscillation circuits in this situation are as follows.

Figure 6 Frequency and load capacitance characteristics

[Countermeasure]

Figure 7 shows a typical crystal oscillator circuit using CMOS IC. By changing the gate capacity CG and drain capacity CD in this figure, the oscillation frequency can be adjusted. Therefore, the following methods can be adopted:

① Choose capacitors with smaller unevenness for CG and CD;

② Choose crystal oscillation units with low sensitivity.

By selecting components based on the above viewpoint, stable frequency accuracy can be obtained.

Our company's products use "QMEMS" technology, which adopts a design that is both small and can suppress sensitivity and unevenness of each product.

Using such products is also an effective means.

3-3.  Oscillation fault caused by low voltage of microcomputer (MPU)

(1) The changing trend of low-power microcomputer (MPU) development

The miniaturization, low power consumption, and multifunctionality of product endpoints are constantly advancing, and the requirements for MPUs that are widely used for various purposes are also the same.

In response to these requirements, the product development of MPU focuses on the following aspects:

·The reduction in the number of semiconductor chips and the trend towards single-chip production;

·The refinement of the design rules adopted (refer to Figure 2);

·Low voltage, low power consumption.

(2) Low power consumption of 32.768kHz oscillation circuit

Compared with this development process, various constraints have also been imposed on the 32.768kHz oscillation circuit. Especially the 32.768kHz clock in MPU

Internally, it is always in a working state and is therefore considered the most important function to achieve low power consumption.

Among them, as sensor networks and ecological products that will receive attention in future application fields, they need to work for a long time under battery drive, so this

The tendency is more significant.

Recently, in order to achieve low power consumption of the 32.768kHz clock, various semiconductor manufacturers have adopted the following for the 32.768kHz oscillation circuit

Various techniques shown. Figure 8 shows one example of the construction of an oscillating circuit block, with different specifications from semiconductor manufacturers.

・Adopting a variable inverting amplifier (with variable voltage gain and variable number of internal inverting amplifiers)

・Adopting variable built-in capacitors

・Adopting a program to reduce the direct current when the inverting amplifier is turned on

Figure 8 Construction of MPU32.768kHz oscillator circuit block embedded inside

[Impact]

Due to the above two changing trends, the trend towards low power consumption is constantly advancing, but it is susceptible to the following negative impacts:

·Weak response to noise;

·Inaccurate oscillation frequency;

·Cannot ensure oscillation margin.

In order to achieve low power consumption and stable oscillation, appropriate evaluation of semiconductor, substrate, and crystal oscillation units will become increasingly important.

[Countermeasure]

It is important to conduct oscillation circuit evaluation tests using actual semiconductors, circuit substrates, and crystal oscillation units during the product design phase. The evaluation test of oscillation circuit may require the manufacturer of crystal oscillation unit to conduct it. Firstly, substrate design will become a key focus. When designing a substrate, please pay attention to the following:

(Refer to Figure 9)

① The oscillation circuit (oscillation unit, oscillation capacitor) should be configured near the oscillation IC (MPU, etc.);

② The substrate wiring should be the shortest and not cross (within 20mm);

③ Configure GND on the lower substrate of the crystal oscillation unit;

④ When using multi-layer substrates, no other signal lines are arranged in the lower inner layer of the crystal oscillator unit.

If the above items are not taken into account in the design, it will cause various faults such as failure to vibrate, unstable oscillation, and inaccurate frequency. Please be aware.

Epson Toyocom is collaborating with semiconductor manufacturers to promote reference activities, and the following key points have been posted on our company's website:

·The composition of semiconductor circuits;

·Our recommended crystal oscillator unit that matches the semiconductor;

·Precautions when designing substrates.

We plan to gradually increase the target semiconductor.

Figure 9 Example of actual substrate installation

3-4.  crystal oscillator 

Unlike the previous "countermeasure" approach, using a "crystal oscillator" in the design is also a very effective countermeasure.

A crystal oscillator is a product that integrates a crystal oscillation unit and an oscillation circuit, and has the following advantages:

・The built-in oscillation circuit ensures that the oscillation action, frequency accuracy, oscillation waveform, and other characteristics are in the optimal state before use;

・No need to change the circuit constants of the oscillating capacitor, nor does it require circuit evaluation of the entire substrate;

・The requirements of stable oscillation and low energy consumption have been adjusted and matched to achieve the highest balance.

Due to these characteristics, it can significantly reduce the design workload and design style of low-frequency oscillation circuits with increasing difficulty

Risk.

Moreover, Epson Toyocom has integrated the crystal oscillator unit and oscillator circuit into a single structure, and has also developed a small-sized SG-3050BC with a size of 2.2 × 1.4 × 1.0tmm. Small in size and only requiring power supply to function, it can contribute to improving the degree of freedom in the installation area.

The above products can provide both small and superior oscillation characteristics simultaneously.

【Epson Toyocom's Ambition】

As described in this chapter, with the progress of miniaturization of crystal oscillation units, performance such as CI value, uneven characteristics, and frequency sensitivity have deteriorated

Road design is more difficult. Epson Toyocom uses the core technology known as "QMEMS" to design and produce products that can simultaneously achieve miniaturization and

A high-performance tuning fork type crystal oscillator unit that contributes to the development of small and high-performance applications.

When producing the tuning fork type crystal oscillator unit, we did not use the mechanical processing method commonly used in production, but instead used a 30 year calendar

QMEMS technology, developed through the evolution of photolithography processing from historical and practical achievements, uses three-dimensional processing to achieve the shape of crystal chips and the formation of electrodes

Small and high-precision tuning fork type crystal oscillator units are carefully designed to achieve optimal characteristics.

Therefore, we can provide customers with tuning fork type crystal oscillation units with the following characteristics:

Using chip etching process to control the unevenness of chip shape (suppress the unevenness of CI value and frequency accuracy);

・A three-dimensional groove is formed on the vibrating arm of the tuning fork to increase the electrode area and achieve a low CI value;

・Perform fine processing to produce smaller products.

・By utilizing the aforementioned QMEMS technology, we have prepared a product lineup that can minimize risks in your design and quality aspects.

In the future, we will continue to advance the evolution of QMEMS technology and strive to develop and provide smaller and higher performance crystal components.

*QMEMS is a registered trademark of Epson Toyocom.

4. Introduction to Epson Toyocom's overall solution for kHz frequency range

Epson Toyocom, as a leading enterprise in crystal components, was the first to develop based on its overwhelming sales performance in the kHz fieldDevelop small and thin products to contribute to customer product development with a comprehensive solution that includes oscillation units and oscillators。

4-1.  Tuning fork type crystal unit

(1) Product lineup of tuning fork type crystal units

The lineup of Epson Toyocom's kHz band tuning fork crystal units is as follows. From columnar to SMD type that can be automatically installed, variety Enriched and applicable for various purposes. Especially for the small main models MC-146 and FC-135, which are world standard specifications and sizes. And also In March 2007, the ultra small FC-12M with high precision, low CI value, and low sensitivity was introduced to the market to cope with the increasingly strong demand for Small scale market demand.

List of tuning fork type crystal units in the kHz frequency band

The trend of miniaturization in FC series

4-2.  32.768 kHz oscillator

(1) Product lineup of 32.768 kHz crystal oscillators

Epson Toyocom has not only prepared a product lineup of 32.768 kHz tuning fork crystal units for you, but also commercialized 32.768 kHz crystal oscillators, which can be used for various purposes just like tuning fork crystal oscillator units. So far, especially for small main players

Model: SG-3030LC has contributed to the development of products for numerous customers.

On top of this, our company has also developed the world's smallest 32.768 kHz crystal oscillator: SG-3050BC, which has excellent performance Higher than our company's existing products.

Overview of 32.768 kHz Crystal Oscillators

■ Overview of 32.768 kHz crystal oscillator specifications

■The trend of miniaturization of 32.768 kHz crystal oscillators

【Regarding Epson Toyocom】

Epson Toyocom was established in October 2005 through the merger of the crystal business of Seiko Epson Corporation and the business of Toyo Communications Corporation.

For crystal based "timing components," "sensing components," and "optical components," the "3D strategy" is based on the concept of "horizontal deployment" of each component and "vertical deployment" of the combination of the three components. We aim to become a leading company in the crystal component industry by providing products to customers worldwide, from the civilian field of mobile terminals to the communication backbone, automotive and other industrial fields.

Our company's "timing components" are crystal quartz products with high precision and stability, and are used as reference signal sources for various instruments and equipment. Vibration of tuning fork in KHz frequency band; AT type crystals that utilize thickness vibration below approximately 100MHz; High Frequency Fundamental (HFF) and Surface Acoustic Wave (SAW) modes utilizing AT vibration technology are available in the hundreds of MHz frequency band, providing customers with various products in the kHz to 2.5GHz frequency range.