1. Mixed-Signal Processing Unit for Sensing Signal Processor NCTU TWT Lab 2011/11/18 (Update)

2. SSP Platform Architecture uP RF Power Module USB Ext. Sensing Actuating Module AFEuni Aux port RTC Aux port Ext Storage Sensor A Sensor B Sensor C Sensor D+AFE Sensor E+AFE Storage uP: 8051/Open RISC RF: Bluetooth USB:USB 1.0 Sensing Signal Processor (SSP)

3. Proposed MSPU Block Digram Temperature Acc. Pressure Humidity Ext. Ch1 Ext. Ch2 Ext. Ch3 Ext. ChN Universal Int. sensor LNA Universal Ext. sensor LNA PGA Filter   ADC Differential Cap. sensing Differential Volt/Cap. sensing Gain Control Gain Control Gain / Filter / ADC Control Logic Gain Control To MCU To MCU SPI Buffer Universal LNA: Gain 2x / 20x PGA: Gain 1x, 2x, 4x, 8x, 16x Filter: TBD ADC Freq: 10kHz max ADC Resolution: 12 bit, 0.8V (FS) System power supply: 1.2V (Revised 11/18/2011) Universal LNA: Gain 2x / 20x PGA: Gain 1x, 2x, 4x, 8x, 16x Filter: TBD ADC Freq: 10kHz max ADC Resolution: 12 bit, 0.8V (FS) System power supply: 1.2V (Revised 11/18/2011) CMRR >100dB 執中 居正 執中 居正 昱賢 志峻

4. Programmable Internal Sensor LNA  The system shall support at least 1x accelerometer ( 執中 ) 1x pressure sensor ( 居正 ) 1x humidity sensor (0~100% RH, 2% res.- 居正 / 物聯網規 格 ) 1x temperature sensor (-20 ⁰ C ~ 60 ⁰ C, 0.5 ⁰ C res..- 志峻 / 物聯網規格 )  Sensing capacitance for pressure and humidity sensors Humidity – 6~7pf with 20% variation on humidity Pressure - <1pf with 5~10% variation on pressure Both humidity and pressure sensor are pure capacitive sensor with single end interface  Need calibration / trim to get accurate measurement  Read-out mechanism needs further study

5. Programmable External Sensor LNA  The system shall support at least 2 channel differential input for 3-lead ECG or auxiliary differential senor input 2 channel auxiliary differential input for touch sensing  ECG voltage range 0.1~4mV  EEG voltage range 10 µ V~200 µ V  Touch/proximity capacitive sensor CS = 5~20pF Sensitivity @ 15fF (ST) or 1fF (ADI) With 12-bit ADC, it ’ s ok for 15fF spec, but difficult to achieve 1fF sensitivity without any improvement on circuit design  need further study

6. ADC Calculation  Consider ADC spec is 0.8 V full scale with 12-bit resolution ( 昱賢 )  Acceelerometer ( 執中 ) Sensor sensitivity at LNA input can be as low as 1mV/g Consider the application for +/-2~16g applications  +/-16g = 32g x 1mV/g = 32mV (gain < 25)  +/-2g = 4g x 1mV/g = 4mV (gain < 200)  Choosing DC gain 20x/160x and 12-bit ADC  +/-16g: 1mV/g x 20 * (2.048LSB/mV) ~= 41 LSB/g >16  +/-2g: 1mV/g x 160 * (2.048LSB/mV) ~= 320 LSB/g >256  Good enough for mobile application  Humidity and Pressure sensor ( 居正 ) Humidity: 6~7pF with 1.2~1.5pF variation  Consider 0~10pF range with 12-bit resolution  2.4fF / LSB  For 1.2~1.5pF variation  500~625 LSBs ~= 9-bit resolution  OK for 物聯網 Pressure: <1pF with 0.05~0.1pF variation  Consider 0~1pF range with 12-bit resolution  0.24fF / LAB  For 0.05~0.1pF variation  200~400 LSB ~= 8-bit resolution BOSCH G-sensor (Used in mobile application)

7. ADC Calculation (cont.)  ECG ( 富彥 / LNA 執中 ) Input range – 0.1~4mV  Max gain < 200 (4mVx200=0.8V full swing ADC range V FS ) Required SNR >=32dB for a good ECG analysis 12-bit ADC ~=74dB SNR  consider 1-bit loss  68dB SNR For 4mV input & 160x gain  640mV / 800mV = -2dB V FS  -2dB V FS + 68dB = 66dB SNR ADC > 32dB (OK!) For 0.1mV input & 160x gain  16mV / 800mV = -34dB V FS  -34dB V FS + 68dB = 34dB SNR ADC > 32dB (marginal !!) For small input ECG, need to increase the gain  LNA stage = 20x / PGA gain = 16x  total gain = 320  SNR = 40dB SNR ADC (good enough!)  EEG Consider the same setting as ECG but input range 10uV~200uV Required SNR >=20dB for good EEG analysis For 10uV input & 320x gain  3.2mV / 800mV = -48dB V FS  -48dB V FS + 68dB = 20dB SNR ADC (marginal!!)

8. ADC Calculation (cont.)  Temperature sensor ( 志峻 ) Based on the textbook (Precision Temperature Sensors in CMOS Technology), a bipolar architecture below generates 2mV/ ⁰ C sensitivity (V BE ) For 2x DC (VGA) gain, we get full range swing (-20~60 ⁰ C) 80 ⁰ C x 2mV x 2 = 320mV < 1V (OK) Resolution: 9-bit ADC 1V = 0.33 ⁰ C / step < 0.5 ⁰ C  Need at least 9-bit ENOB  12-bit ADC is good enough Temperature Sensor

9. Summary (11/18)  Based on accelerometer sensitivity @ 1mV/g Internal sensor LNA gain = 20 VGA gain = 1, 2, 4, 8  Based on Temperature sensor sensitivity @ 2mV/ ⁰ C VGA gain = 2  With 12-bit, 0.8V full scale ADC Accelerometer can support  +/-2g with > 200 LSB / g resolution & +/-16g with > 40 LSB / g resolution  LNA+VGA gain up to 160x to improve +/-2g resolution to >256LSB/g Temperature sensor can support  Better than 0.33 ⁰ C resolution Humidity/Pressure ( 執中 ) internal sensors  direct 12-bit ADC conversion may provide 8~9bit resolution within the sensing range ECG ( 富彥 / 居正 ) external sensors support with 12-bit ADC requires maximum 320x to achieve target SNR for 0.1mV small ECG signal EEG signal can be as small as 10uV  320x gain stage + 12-bit ADC provides only marginal performance. Need further investigation  ADC sampling rate @ max 10kHz shall be capable of polling 8 sensors at >=1kHz sampling rate However, LPF for SNR improvement cannot be performed if shared LNA