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

1. Reciprocal counting method
2. 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