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Along with the spread of smartphones and tablet terminals, the market for wearable devices for watches and eyeglasses, which incorporate functions for health care and sports, is expanding rapidly. Since wearable devices are used outdoors for a long time without a power source, in addition to making wearable devices smaller by wearing them, they are also extremely demanding in terms of current consumption reduction. Normally, wearable devices are equipped with a standard signal source in the MHz band, such as for microcomputer control and short-range radio, and a reference signal source in the 32.768kHz for watches. Oscillating circuits are used for each signal source. However, due to the miniaturization of wearable devices, the board mounting area has become smaller year by year, and space-saving is required.
In response to these needs, we have realized a compact crystal oscillator for clocks (hereinafter referred to as “dual-wave output oscillator”) that can output two waves simultaneously.
2. Output characteristics
·It is possible to output the specified MHz output and 32.768kHz two waves simultaneously from one oscillator, but it is also possible to switch from dual-wave output (MHz + kHz) to 32.768kHz single-wave output by switching the mode terminal.
·As will be described later, the current consumption at single-wave power (32.768kHz) is Max.1uA, which achieves ultra-low current consumption.
3. Structure of dual-wave output oscillator
The crystal blank on which the electrodes was formed and the IC that was developed jointly with IC manufacturers and capable of outputting two waves were mounted on a ceramic package to achieve a one-chip design. In addition, the simulation tool was used to arrange IC pads and design ceramic package patterns, and two frequencies (32.768kHz and MHz) could be output by using a design that minimizes the mutual interference between the two frequencies.
4. Benefits of using dual-wave output oscillator
(1) Significantly reduces the component count
When the MHz output is used for short-range radio and microcomputers, and 32.768kHz for RTCs, an oscillator circuit is required for each of MHz and 32.768kHz. Each oscillator circuit is composed of a crystal unit, a resistor, and two capacitors. When a dual-wave output oscillator is used, it is possible to reduce the number of mounted components from eight to one. Example of Oscillator Circuit Configuration of Microcomputer and Chipset
(2) Space savings
By reducing the number of mounted parts, space saving can be achieved. As shown in the table below, the use of a two-wave output oscillator for 32.768kHz (3215 size) + MHz (2520 size) + resistor + capacitor saves about 70% of space.
(3) Component mounting failure and cost reduction
By reducing the number of mounted parts (8 parts → 1 part), mounting failure and mounting cost are reduced to 1/8.
(4) Simplification of circuit design
Examples of designing board circuits are shown below.
(5) Current consumption reduction
Under the condition of VCC=+1.8V and no load, the dual-wave output oscillator (NZ2016SK), which we have lined up, realizes an ultra-low current consumption of Typ. 0.8μA at the time of single-wave output, which saves current consumption by about 1/10 compared with our conventional product (NZ2520SHB).
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