MIXED SIGNAL VLSI TECHNOLOGY BASED SoC

DESIGN FOR TEMPERATURE COMPENSATED

pH MEASUREMENT

S. K. Tilekar1, A. S. Powar1 and B. P. Ladgaonkar1

1- VLSI Design & Research Centre

Post Graduate Department of Electronics

Shankarrao Mohite Mahavidyalaya, Akluj, Dist. Solapur (MS)

t_shivaprasad@rediffmail.com, bladgaonkar@yahoo.com

Abstract

An innovative field of embedded system exhibit wide

spectrum of applications particularly in the field of

instrumentation [1]. The VLSI devices like FPGA and CPLD

provide the reconfigurability for digital design only. Therefore,

for analog parts, the designers have to rely on off chip

hardware. This exhibits constraints in instrumentation [2]. The

emergence of the innovative technology called mixed signal

based VLSI design provides unique solution to above problem

[3]. Cypress semiconductor is performing pioneering job in the

field of mixed signal based programmable system on chip and

vendoring the PSoC5 device with remarkable features [4].

Deploying the features of PSoC5, a system on chip is designed

for temperature compensated pH measurement of the solution.

Keyword: Mixed Signal PSoC5, ADC, Programmable Gain

Amplifier, pH measurement.

Op

amp

LP

filterA/D Microcontroller

Op

ampD/A

Sensor

Digital Outputs

LEDs

Competitive Solutions

Op

amp

LP

filterA/D Microcontroller D/A

Sensor

Digital Outputs

LEDs

PSoC Microcontrollers

Soft as well as hard IP Cores

FPGA platform

Core of the computing device

Specific IDE for system development

SoB to SoC

Static as well as Dynamic configurability IP Cores

FPGA platform

Advanced microcontroller Core (ARM Core)

Specific IDE for system development

P rogrammable

S ystem

o n

C hip

– Hardware programmability

Programmable analog blocks

Programmable digital blocks

Programmable interconnect

Programmable I/Os

Programmable clocks

Selectable power supply

– Integration as an SoC

32-bit ARM Cortex-M3 CPU core DC to 80 MHz operation

Flash program memory, up to 256 KB, 100,000 write cycles, 20-year retention, and

multiple security features

Up to 64 KB SRAM memory

2-KB electrically erasable programmable read-only memory (EEPROM) memory, 1

million cycles, and 20 years retention

Low voltage, ultra low power Wide operating voltage range: 0.5 V to 5.5 V

Low power modes including: 2-μA sleep mode

Versatile I/O system 28 to 72 I/Os (62 GPIOs, 8 SIOs, 2 USBIOs)

LCD direct drive from any GPIO, up to 46×16 segments

All GPIOs configurable as open drain high/low, pull-up/pull-down, High-Z, or strong output

Configurable GPIO pin state at power-on reset (POR)

Digital peripherals 20 to 24 programmable logic device (PLD) based universal digital blocks (UDBs)

Full-Speed (FS) USB 2.0 12 Mbps using internal oscillator

Four 16-bit configurable timers, counters, and PWM blocks

Library of standard peripherals

Library of advanced peripherals

Analog peripherals 1.024 V ±0.1% internal voltage reference across –40°C to +85°C (14 ppm/°C)

Configurable delta-sigma ADC with 8- to 20-bit resolution

Two SAR ADCs, each 12-bit at 1 Msps[2]

80-MHz, 24-bit fixed point digital filter block (DFB) to implement finite impulse

response (FIR) and infinite impulse response (IIR) filters

Four 8-bit 8 Msps current IDACs or 1-Msps voltage VDACs

Four comparators with 95-ns response time

Four uncommitted opamps with 25-mA drive capability

Four configurable multifunction analog blocks. Example configurations are

programmable gain amplifier (PGA), transimpedance amplifier (TIA), mixer, and

Sample and Hold

Programming, debug, and trace

Precision, programmable clocking

Voltage output ranges: 1.020-V and 4.080-V full scale

Software- or clock-driven output strobe

Data source can be CPU, DMA, or Digital components

Gain steps from 1 to 50

High input impedance

Selectable input reference

Adjustable power settings

Single or differential connections

Adjustable between 2 and 32 connections

Software controlled

Connections may be pins or internal sources

No simultaneous connections

Bidirectional (passive)

Selectable resolutions, 8 to 20 bits (device dependent)

Eleven input ranges for each resolution

Sample rate 10 sps to 384 ksps

Operational modes:

Single sample

Multi-sample

Continuous mode

Multi-sample (Turbo)

High input impedance input buffer

Selectable input buffer gain (1, 2, 4, 8) or input buffer

bypass

Multiple internal or external reference options

Automatic power configuration

Up to four run-time ADC configurations

Implements the industry-standard Hitachi HD44780 LCD display Driver

chip protocol

Requires only seven I/O pins on one I/O port

Contains built-in character editor to create user-defined

Custom characters

Supports horizontal and vertical bar graphs

Linear current output: 1 μA/K

Wide temperature range: −55°C to +150°C

2-terminal device: voltage in/current out

Laser trimmed to ±0.5°C calibration accuracy (AD590M)

Excellent linearity: ±0.3°C over full range (AD590M)

Wide power supply range: 4 V to 30 V

Sensor isolation from case

Low cost

1) The visual method

2) The photometric method

3) The potentiometric method

E = Eo – K Tk pH

Nernst Factor

K = 0.19841 (273.15+T oC)

Execute boot program:

--initialise general purpose resources;

--configure application specific modules;

--initialise run time environment;

--disable interrupt;

call main application routine;

Void main()

{

Start system timers;

Initialise application specific modules;

Initialise global variables;

Initialise application specific channels;

Enable interrupts;

While(1)

{

Wait for events(Enabled interrupts);

Read values from input channels;

Execute control procedure & compute

actuation data;

output actuation data to output

channels;

}

}

B) Application programme routine

A) Boot programme algorithm

STRUCTURE OF FIRMWARE

#include <device.h>

#include <stdio.h>

float pH_Input_Signal();

float Temp_Input_Signal();

void soft_delay(unsigned int count);

int i=1,j=1;

float result=0,pH_Result,Average_pH,pH_value,pH_Temp_Copensated,pH_valueDirect;

float Temp_Result,Temp_value,Average_Temp,Temp_Calibrated;

void main()

{

char pH_Str[5]={'\0'};

PGA_1_Start(); PGA_2_Start(); VDAC8_1_Start(); LCD_Char_1_Start();

ADC_DelSig_1_Start(); char Temp_Str[4]={'\0'}; AMuxSeq_1_Start();

while(1)

{

AMuxSeq_1_Next(); LCD_Char_1_Position(0,0); LCD_Char_1_PrintString("T:");

Temp_Result=Temp_Input_Signal(); Temp_value = Temp_Result-273;

Temp_Calibrated=(Temp_value+0.7503)/1.0377;

LCD_Char_1_Position(0,2); sprintf(Temp_Str,"%4.2f",Temp_Calibrated);

LCD_Char_1_PrintString(Temp_Str);

MuxSeq_1_Next();

LCD_Char_1_Position(1,0); LCD_Char_1_PrintString("pH:");

pH_Result=pH_Input_Signal();

pH_value = (pH_Result)/(0.19841*(273.15+Temp_Calibrated)); //Nernst equation

LCD_Char_1_Position(1,3); sprintf(pH_Str,"%5.2f",pH_value);

LCD_Char_1_PrintString(pH_Str);

pH_valueDirect = ((pH_Result-24)/59.16); LCD_Char_1_Position(0,9);

sprintf(pH_Str,"%5.2f",pH_valueDirect); LCD_Char_1_PrintString(pH_Str);

} }

float pH_Input_Signal()

{

float total=0,Sampling_Rate=1000;

for(i=1;i<=Sampling_Rate;i++)

{

ADC_DelSig_1_StartConvert();

ADC_DelSig_1_IsEndConversion(ADC_DelSig_1_WAIT_FOR_RESULT);

total=total+ADC_DelSig_1_GetResult16();

soft_delay(1000);

}

Average_pH=((total/Sampling_Rate)*3);

return(Average_pH);

}

float Temp_Input_Signal()

{

float total=0,Sampling_Rate=750;

for(j=1;j<=Sampling_Rate;j++)

{

ADC_DelSig_1_StartConvert();

ADC_DelSig_1_IsEndConversion(ADC_DelSig_1_WAIT_FOR_RESULT);

total=total+ADC_DelSig_1_GetResult16();

soft_delay(2000);

}

Average_Temp=((total/Sampling_Rate)*4);

return(Average_Temp);

}

y = 1.0515x - 3.22

R² = 0.9989

0

20

40

60

80

100

120

0 50 100 150

Temperature in oC from Thermometer

Tem

pe

ratu

re in

oC

fro

m S

yste

m

Temp Measured

(Thermometer)

Temp Measured

(PSoC)

40 39.94

45 44.94

50 49.97

55 54.93

60 59.95

65 64.95

70 69.91

75 75.01

80 80.01

85 85.02

90 90.41

95 95.52

100 100.56

Temp Measured in oC

(Thermometer)

Temp dependent

NERNST volt in mV

From system (PSoC)

Temp dependent

NERNST volt in mV

From datasheet

20 58.18 58.16

25 59.17 59.16

30 60.16 60.15

35 61.13 61.14

40 62.13 62.13

45 63.14 63.12

50 64.13 64.12

55 65.12 65.11

60 66.12 66.10

65 67.11 67.09

70 68.09 68.08

75 69.10 69.08

80 70.09 70.07

The system is calibrated to pH scale and

implemented for measurement of temperature compensated

pH of the solution. The pH value shown by the system under

investigation are identical to that of measured by standard

pH meter. Thus SoC designed to measure pH of the solution

is more reliable and accurate.

1) Y. Sukanya, S. Pathapati, “FSK Modem Using PSoC”, International journal of

soft computing and engineering, 2 3 (2012) 451.

2) L.M. Franca-Neto , P. Pardy, M.P. Ly, R. Rangel, S. Suthar, T. Syed, B. Bloechel,

S. Lee, C. Burnett, D. Cho, D. Kau, A. Fazio and K. Soumyanath, “Enabling

High-Performance Mixed-Signal System-on-a-Chip (SoC) in High Performance

Logic CMOS Technology”, Symposium on VLSI Circuits Digest of Technical

Papers, (2002)164-167.

3) L.S.Y. Wong, S. Hossain, A. Ta, J. Edvinsson, D.H. RivasandH. Naas, “A very

low-power CMOS mixedsignal IC for implantable pacemaker applications” IEEE

Journal of Solid-State Circuits, 39 12 (2004) 2446-2456.

4) M. Nagata, J. Nagai, T.Morie and A. Iwata, “Measurements and Analyses

ofSubstrate Noise Waveform in Mixed-Signal ICEnvironment,” IEEE

Transactions on CAD, 19 6 (200) 671-678.

5) K. Makie-Fukuda, T. Kikuchi, T. Matsuura, M. Hotta, “Measurement of digital

noise in mixed-signal integrated circuits”, IEEE Journal of Solid-State Circuits,

30 2 (1995) 87-92.

Research Activities

MRP : 01 Completed

Publications

: International Journals 01

: International Journals (Communicated) 01

: National Journals 01

: National Journals (Communicated) 01

: Proceedings International 02

: Proceedings National 42

Papers presented in conferences

: International 01

: International (Abroad) 01

: National 12