T.C. DOĞUŞ UNIVERSITY

CEE 426Microelectronic Analog Circuit Design

Opamp Analysis

AD8538ARZ

By

Tolgahan ŞUSUR

200934005

AD8538ARZ

INTRODUCTION

Analog Devices Inc. announced a series of low-cost amplifiers that operate at low voltages and consume minimal power without sacrificing the accuracy required by portable applications that need precise signal conditioning. To extend battery life, amplifiers must offer very low operating and standby power, low-voltage operation, and rail-to-rail outputs.

Auto-zero Amplifier

The AD8538 offers the industry’s best accuracy

versus power among auto-zero amps on the market, and is ideal for signal paths with very low offset voltage and offset voltage drift over time and temperature.

More about the AD8538

Requiring a supply current of only 150 microamps, the AD8538 offers three times better temperature drift performance compared to the closest competing device a drift performance level equivalent to products requiring over 1 mA of supply current. Its low power and high precision makes the AD8538 well-suited for markets such as medical equipment, pressure and thermal sensors and automotive electronics.

With only 0.01 microvolt/degree C offset drift, the AD8538 offers the industry’s lowest offset drift at low operating current. The device offers tremendous cost and time savings to designers as compared to a discrete system-level auto-calibration approach, which requires more complicated and costly hardware and software that can slow down time-to-market for new products. The device’s outstanding precision – 12 microvolts maximum offset and just 1 microvolt p-p of low-frequency noise — enable highly accurate and stable system designs without the cost, size and complexity of solutions utilizing external auto-calibration.

Applications

For the AD8538, typical high-resolution portable sensor applications, such as IR thermal scanners, require very low offset and offset drift to achieve accurate measurements.

Pricing and Availability

The AD8538, available now in production quantities, is packaged in both TSOT-23 and narrow SOIC-8 packages and is priced at $0.89 per unit in 1,000-piece quantities.

Brief properties

The AD8538 is a very high precision auto-zero amplifier that features extremely low offset voltage and low input bias current while consuming low power. The supply current is less than 180 µA at 5.0 V. Operation is fully specified from 2.7 V to 5.0 V single supply (±1.35 V to ±2.5 V dual supply). The AD8538 offers tremendous cost and time savings to designers as compared to a discrete system-level autocalibration approach, which requires complicated and costly hardware and software that can slow down time-to-market for new products. The AD8538 amplifier is available in 5-lead TSOT-23 and 8-lead SOIC and is specified over the extended industrial (–40°C to +125°C) temperature range. The application circuit's closed-loop gain is set for 101

Using for ;

Mobile Communication Portable Instrumentation Battery Powered Devices Sensor Interface Temperature measurement Electronic Scales

Figure.1: AD8538 Thermometer circuit

MEASUREMENTS AND SIMULATIONSIn my measurements , I use PSPICE and PROTEUS softwares. But ı rarely use PROTEUS because ıt is easy to get measurement also there is more component library than PSPICE . In addition there is more graphical properties and very user friendly menus for simulations. For simulation I apply buffer and non inverting circiut with AD8538ARZ. In simulations I use Pulse,DC and Sin waves

Figure.2: All circuit and Pulse generator properties for Buffer circuit

Figure.3: Pulse Generator amplitude and Frequency (+-15 volt)

RATED VOLTAGES OF AD8538ARZ

Figure.4:Vout , output voltage (Supply voltages are +-15v)

As we can see above in figure 4 there is a rated voltage which is +-14 volt .

SLEW RATE OF AD8538ARZ

Figure.5:Slew rate is 0.45v/us (Supply voltages are +-3v)

FREQUENCY ANALYSIS OF AD8538ARZ

Figure.6:Frequency responce analysis, fb=632kHz ft=50MHz A0=45dB=177.8

There is a some problems about gain because ft=fb*A0=50Mhz =632kHz*A0

A0=79 But my graph value 177.8 so there is conflict or my measurement is false.

INPUT CURRENT AND EMPEDANCE OF AD8538ARZ

R1=1K

R2=1K

Figure.7: Input voltage and input empedance, input current (Input=4v DC )

We can see that our input voltage=4 volt input current=18pA so input empedance 4/18pA=222G ohm. So there is a high empedance at input like infinite

OFFSET VOLTAGES OF AD8538ARZ

Figure.8 Offset voltages

There is gain 1/1+1=2 and our vout value is 115uV/2=57.5uV offset voltage

R1=1K

R2=1K Vsupply=+-15v

SETTLING TIME OF AD8538ARZ

Figure.9: Settling time (input +10m-0v pulse wave supply :+-15v dc)

We can calculate the settling time with these steps;

10.5mv (hill point of vout )-10mv/10mv =0.05

100*0.005=%0.5 settling time

SUPPLY CURRENT OF AD8538ARZ

Figure.10:Supply current (Buffer circuit)

As we can see above ı measure the current with dc ammeter and ı see that values

Input current =0.33mA=330uA

REFERENCE

1. http://www.radiolocman.com/news/new.html?di=4499

2. http://www.analog.com/static/imported-files/data_sheets/AD8538_8539.pdf