Dual-MEMS-Resonator Temperature-to-Digital Converter with 40µK Resolution and FOM of 0.12pJK2
IEEE International Solid-State Circuits Conference 2016
Precision Oscillator Applications
Precision Oscillator Resonators
MEMS-Based Programmable Oscillator Package
MEMS die, CMOS die and leadframe in a package
MEMS-Based Programmable Oscillator (XO)
Output stability matches reference resonator
MEMS-Based Programmable Oscillator (TCXO)
Temperature-to-Digital Converter (TDC) is needed
TDC Specifications
State-of-the-Art TDCs
Prior Architectures Unsuitable
Dual-MEMS Resonator TDC
Different temperature coefficients (TC) for two clocks:
- Frequency ratio indicates temperature
- TempSense clock (ClkTS): TC = -7ppm/K
- TempFlat clock(ClkTF): TC < 1ppm/K
Frequency Ratio Measurement Techniques
- Reciprocal counting method
- Counts OSC1’s number of cycles in a time window set by OSC2 and counter2
Proposed Ratio Engine
Implementation Flow
More Details
Digital PFD
Chip Micrograph
- 0.18µm CMOS
- 0.54mm2 (Resonator included)
- 12mA current for:
- Sustaining circuits
- Frequency ratio engine
- Digital
- Supply voltage: 1.6V
Resolution Measurement Setup
Thermal insulator is needed
Environmental noise dominates the TDC resolution
Resolution Measurement Setup
Instead of TDC output, clock PN is measured
TDC Contribution on PN
TCXO with Gained-up TDC
TDC has 40µK resolution over a BW of 130Hz
MEMS Resonators’ Stability Measurements
Measured TCXO’s Stability
Allan Deviation Measurement
TCXO meets the ADEV target of < 1e-10
Comparison Table
Energy/Conversion vs. Resolution
Resolution FOM = (Energy/Conversion)×Resolution2
Resolution FOM = (Energy/Conversion)×Resolution2
Conclusions
1. The first of a new category of the temperature sensors
2. Dual-MEMS-Resonator TDC:
- Resolution of 40µK → 2.5x improvement
- Resolution FOM of 0.12pJK2 → 5.5x improvement
3. MEMS-Based Oscillator for telecom applications:
- Allan Deviation of < 1e-10 in 1s averaging time
- Frequency stability of < ±0.1ppm
- Temperature range of -40°C to 85°C
Acknowledgement
- Prof. Kofi Makinwa for his support, review, and comments!
- Nazariy Tshchynskyy, Anton Prygrodskyi and Trushal Chokshi from SiTime for their dedicated support during the measurements