PRAMPS in lab and field instrumentation
Analytical lab equipment can be used for early detection of diseases and drug development in life sciences. Apparatuses for mass spectrometry, spectroscopy and chromatography require a high level of accuracy. Precision amplifiers are a critical part of the design for signal conditioning and analog signal processing.
Field instrumentation equipment includes a broad range of measurements including liquid analysis, pressure, and temperature monitoring. Portable field instruments such as data loggers and process control require low power and low noise to maximize efficiency without degrading the accuracy of the measurement.
Figure1. Typical block diagram for signal conditioning block with high accuracy
In figure 1 the OPA2206 provides the protection (up to 40V) which may be needed against voltages that are much higher than the operating range of 36V. The OPA2206 has super beta input transistors which reduce the input bias current substantially compared to other bipolar devices. As a result of its super beta inputs, the OPA2206 has a high input impedance and a very low current noise which make it versatile for various analog signal processing including buffering high voltage signals.
In the next stage, the THP210 is used as a differential amplifier to drive a high-resolution ADC. The very low noise floor and the differential output increase noise immunity which minimizes the impact on the ADC and helps maintain the overall system ENOB to adequate levels. In addition to the THP210 as a differential driver, the OPA2182 is used as a reference buffer. The zero-drift op amp provides a very low offset drift of 12nV/C and allows the system designer to avoid complex calibration schemes. The zero-drift topology virtually eliminates the 1/f component thereby increasing the accuracy of the overall system.
Table 1. Recommended precision op amps for lab instrumentation
|
Specifications |
OPA2387 |
OPA197 |
THP210 |
OPA391 |
|
System benefit |
Super precision |
Mux friendly |
Ultra-low noise |
Micro power zero drift |
|
Supply Range (V) |
1.7 to 5.5 |
4.5 to 36 |
3 to 36 |
1.7 to 5.5 |
|
GBW (typ, MHz) |
5.7 |
10 |
9.2 |
1 |
|
Input Offset (max, µV) |
15 |
100 |
40 |
45 |
|
Input Offset Drift (typ, µV/°C) |
0.003 |
0.5 |
0.1 |
1 |
|
Noise @ 1kHz (typ, nV/rtHz) |
8.5 |
5.5 |
3.7 |
60 |
|
Iq per Channel (max, mA) |
0.57 |
1 |
0.95 |
0.024 |
|
Output Current (typ, mA) |
55 |
60 |
31 |
60 |
Table 2. Recommended precision instrumentation amplifiers for lab and field instrumentation
|
Specifications |
INA821 |
INA826 |
|
System benefit |
High input Z, High CMRR |
Low power high CMRR |
|
Supply Range (V) |
4.5 to 36 |
4.5 to 36 |
|
GBW (typ, MHz) |
5 |
1 |
|
Input Offset (max, µV) |
35 |
150 |
|
Input Offset Drift (typ, µV/°C) |
0.4 |
2 |
|
Gain drift (ppm / °C) |
5 |
1 |
|
Noise @ 1kHz (typ, nV/rtHz) |
7 |
18 |
|
Iq per Channel (max, µA) |
650 |
200 |
For portable field instrumentation equipment, precision low power op amps help improve the system efficiency while maintaining signal integrity.
Table 3. Recommended very low power precision op amps
|
Specifications |
LPV821 |
OPA369 |
|
System benefit |
Very low drift, nano power |
Zero cross over very low power |
|
Supply Range (V) |
1.7 to 3.6 |
1.8 to 5 |
|
GBW (typ, kHz) |
8 |
12 |
|
Input Offset (max, µV) |
10 |
0.75 |
|
Input Offset Drift (typ, µV/°C) |
0.02 |
0.4 |
|
Noise @ 1kHz (typ, nV/rtHz) |
215 |
290 |
|
Iq per Channel (max, µA) |
0.650 |
0.8 |