Flow sensor circuitry Eduard Stikvoort 00/1A The work was done in Philips Reaearch Eindhoven

1.0 Overview 01/1A 1 Introduction 2 Amplifiers 3 A/D 4 Comparator 5 Test ICs 6 Discussion 7 Conclusions

1.1 Introduction 02/1A - wireless flowsensor for infuse pumps - sensor heats the liquid (e.g. 1 degree) and measures temperature difference - output of the sensor is a few mV - powered by incoming E.M. field - output data transmitted IC process: 0.18 um CMOS

1.2 Overview flow sensor 03/1A

2.0 Amplifiers 04/1A

2.1 Switched Cap. amplifier 05/1A OTA

2.2 Two-phase operation 06/1A

2.3 OTA circuit 07/1A bias current 0.7 uA

2.4 Simulation results S.C. Amp. 08/1A simulated input, output and clock

2.5 IC-output buffer 09/1A for driving off chip load oscilloscope + cable e.g. 50 pF Bias current 150 uA MHz in 68 pF

0A/1A simulated frequency response off-chip output (load = 68 pF) 2.6 Simulation IC-output buffer

3.0 A/D 0B/1A cold side capacitors to ground or regulated supply comparator input to Vstab/2 = Vref input sampled in capacitor bank (MSB=1, other bits 0)

3.1 A/D input range 0C/1A

3.2 A/D timing diagram 0D/1A

3.3 Thermometer coding 3 MSB's 0E/1A - improves linearity when segments spread

4.0 Comparator circuit 0F/1A comparator output latch input stage NOR flipflop Clad

4.1 Comparator simulations 10/1A input, output and clocknot output changes with delayed clocknot

5.0 Test ICs 11/1A - input amplifier - 1x amplifier, IC-output Amp. - comparator - A/D

5.1 Test IC with first amplifier 12/1A

5.2 Layout of amplifier IC 13/1A

5.3 Test IC with 1x amplifier 14/1A IC ouput buffer output + 1x S.C. Amp.

5.4 Test IC with comparator 15/1A

5.5 Test IC with A/D 16/1A

5.6 A/D test IC 17/1A supplies: - stabilised - digital - for I/O one ground MIM capacitors (M5/M6, M4 shield) on top of the circuit

6 Discussion 18/1A - signal path was presented, other parts were not (clock oscillator, timing, modulator, supply, stabiliser, transmitter) - adjustable gain for uncertenty of sensor sensitivity - 2 switched cap. amplifiers (gain of the OTA) - gates of the SAR directly drive the bit capacitors - standard logic not used for less dissipation

7 Conclusions 19/1A - test ICs for a wireless flow sensor - switched capacitor amplifiers, latched comparator - 10 bits A/D - test ICs have home-made analogue IC-ouput, standard digital I/O