SiTime enters wearables, IoT markets with 32 kHz MEMS TCXO
This product is featured in EDN's Hot 100 products of 2014. See all 100 here.
The company uses its TempFlat MEMSTM (See my article on SiTime’s MEMS Resonators: An alternative to Quartz) and analog technology to attain some really excellent specifications. The SiT1552 MEMS TCXO is 20% of the size and consumes 50% of the power of comparable quartz devices. See Figure 1 for the architectural diagram of this device.
Figure 1: MEMS TCXO architecture
Stability over temperature
Here is the amazing accomplishment in this device. The previous solution which is still a good solution for many designs is the SiT153x, a 32 kHz XO @ 100 ppm stability---this device is great for the mobile and tablet market. The newer device SiT1552, a 32 kHz TCXO has +/- 5 ppm stability----wearables, sport fitness, personal medical devices, accessories and the IoT and are the market for this device where ultimate accuracy, increased battery life and small size are critical. See Figure 2.
Figure 2: The SiT153x frequency stability over temperature vs. the SiT1552
The following video tells the complete story about this device:
The device is available in a 1.5 x 0.8 mm chip scale package (CSP). See Figure 3.
Figure 3: Showing the unique packaging to obtain the smallest size possible
The device can perform various functions in a system such as:
- Reference for real time clock (RTC) function
- Sleep clock for connectivity – Bluetooth, Bluetooth Low Energy, WiFi
- Heartbeat clock for battery supervisory function
Extending battery life
Now we get to one of the most important aspects of this design---extending battery life of the device in which it will reside. This is what really blew my mind. Here is how it does just that:
- Problem: Frequent network connections consume power, limits battery life.
- Solution: 5 PPM 32kHz sleep-clock maximizes battery life
- On Time and Sleep Time are defined in BLE standards
- Early On Time is penalty due to clock inaccuracy (worse stability)
- Tighter Stability à Shorter Early On Time à Lower Power
Figure 4: This 5 ppm TCXO extends battery life
Now let’s compare a 180 ppm Quartz resonator with the 5 ppm MEMS TCXO . See Figure 5.
Figure 5: This graph clearly shows the Quartz resonator at 180 ppm; The MEMS TCXO at 5 ppm with 10 ms On Time and at 3 ms On Time depending upon Sleep Time
Editor’s note: Even in high throughput systems, a BLE device transmits only for a small percentage of the total time the device is connected. In addition to transmitting, a BLE device will most likely go through several other states, such as receiving, sleeping, waking-up from sleep, etc… Even if a device’s current consumption in each different state is known, this is still not enough information to determine the total power consumed by the device. The different layers of the BLE stack all require certain amounts of processing in order to remain connected and comply with the protocol’s specifications. The MCU takes time to perform this processing, and during this time current is consumed by the device. In addition, the device might take some time when switching between states. All of this must be taken into account in order to get an accurate measurement of the total current consumed. (From Texas Instruments Application Note #AN092) All-in-all this SiTime SiT1552 resonator is impressive vs. any Quartz resonator.
Compared to a quartz TCXO, the SiT1552 MEMS TCXO is:
- 20% of the size and is available in a 1.5 x 0.8mm CSP
- 50% lower power, typically consuming less than 1 micro-amp
- 45% thinner, with a height of 0.55 mm
- 10 times faster startup, with a startup time of 0.3 seconds
- 30 times higher shock resistance
- 15 times higher reliability, at 500 million hours MTBF
Additional features of the MEMS IC include:
- ±5 PPM frequency stability that enables 2 to 3 times longer battery life compared to a 180 PPM quartz resonator
- NanoDriveTM, a programmable, low swing output that minimizes power and directly interfaces to the oscillator / RTC circuit in the downstream processor or PMIC
- 1.5 to 3.63V operation, making it ideal for products that use a coin-cell or super-cap battery backup
Figure 6: The SiTime device is capable of driving multiple loads
For more information and datasheets, visit the SiTime website.