LINEAR AN78-1 Data Manual

Application Note 78 August 1999

A Collection of Differential to Single-Ended Signal Conditioning Circuits for Use with the LTC2400, a 24-Bit No Latency ∆Σ ADC in an SO-8 By Kevin R. Hoskins and Derek V. Redmayne

INTRODUCTION The LTC®2400 is the industry’s first No Latency ∆ΣTM ADC power differential-to-single-ended signal conditioning cir- that combines automatic offset and full-scale calibration, cuits. These circuits offer the customer a number of an internal oscillator, a sinc4 digital filter, and serial I/O to choices for conditioning differential input signals as low as yield a 24-bit ADC with 1.5µVRMS input noise and single- 5m V to as high as ±2.5V, as well as operation on a single shot conversion time architecture. It is the ideal 5V or ±5V supplies. In each case, careful circuit design and A/D converter for temperature measurement and high implementation techniques were used to maintain or pre- effective resolution instrumentation applications, such as serve the LTC2400’s inherently high effective resolution. digital multimeters. In some cases, circuit accuracies (uncalibrated) exceed

17 bits.

This application note contains six circuits that

, LTC and LT are registered trademarks of Linear Technology Corporation.

extend the LTC2400’s capabilities using a number of low No Latency ∆Σ is a trademark of Linear Technology Corporation.

TABLE OF CONTENTS

Circuit 1. LTC2400 High Accuracy Differential to Single-Ended Converter for 5V Supplies.................... AN78-2

Differential to Single-Ended Converter Has Very High Uncalibrated Accuracy and Low Offset and Drift

Circuit 2. Simple Differential Front-End for the LTC2400 ........................................................................AN78-4

Simple Rail-to-Rail Circuit Converts Differential Signals to Single-Ended Signals and Operates on Single or Dual Supplies Where Resolution Is More Important Than Accuracy

Circuit 3. Bipolar Input 24-Bit A/D Converter Accepts ± 2.5V Inputs AN78-6

Differential Input 24-Bit A/D Converter Provides Half-Scale Zero for Bipolar Input Signals

Circuit 4. High Accuracy, Differential to Single-Ended Conversion for Wide Range Bipolar

Input Signals AN78-8 Bipolar Differential to Single-Ended Converter Drives the LTC2400’s Input Rail-to-Rail

Circuit 5. Low Level, High Accuracy, Bipolar Input Differential to Single-Ended Signal

Conversion for 24-Bit A/D AN78-10 Single Supply Differential to Single-Ended Conversion Circuit Amplifies Low Level Bipolar Signals and Maintains the LTC2400’s High Accuracy

Circuit 6. LTC2400 High Accuracy Differential to Single-Ended Converter for Single 5V Supply AN78-12

This Converter Has High Accuracy, Very Low Offset and Offset Drift, Rail-to-Rail Input Common Mode Range and is “Live at Zero”

LTC2400 Bonus Circuits

#1: An Extremely High Resolution LTC2400-Pt RTD Temperature Digitizer AN78-14 #2: A High Resolution LTC2400-Based Type S Thermocouple Temperature Digitizer with Improved Cold Junction Compensation AN78-15 LTC2400 Key Specifications Summary AN78-16

an78fs

AN78-1