Maximize Signal Integrity in Scientific and Field Instrumentation

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When designing scientific equipment and electronic instruments, captured signal characteristics and environmental factors can present obstacles. For example, while designing a power analyzer or sensor to measure environmental parameters, the captured signals are likely transient and have very low voltage or current. Additionally, noise, temperature variations, and outside interference may significantly degrade them. Other examples of instruments that require precision design and reliable performance are spectroscopy systems or field-deployable measurement equipment. Whatever the end application, instrumentation system performance hinges on the capability of the operational amplifiers (op-amps) used in the design.

However, selecting op-amps for instrumentation can be challenging, as most op-amps face several trade-offs, such as precision for speed, noise performance for power, and drift for settling time. So, how does a designer overcome these constraints when an instrument design depends on signal fidelity?

This blog discusses why selecting the proper op-amp capable of upholding signal fidelity without sacrificing performance metrics is crucial for achieving accurate, reliable instrumentation.

The Challenge: What Precision Really Demands

Realizing precision in the instrumentation landscape is a challenge that varies depending on the end-application. Achieving precision measurements depends largely on the signal dynamics of the captured signals and the environmental factors of a given application. For instance, with test and measurement applications, signals often vary widely, can include high amplitudes and broad common-mode swings, and typically require fast settling times due to their time-dependent nature. Scientific instruments deployed to monitor over long periods often prioritize long-term stability, minimal thermal drift, and minimal recalibration requirements.

On the other hand, field instruments are usually highly constrained by their power sources; hence, they have low operating power budgets but still need to maintain high signal integrity.

For most applications, trying to reduce drift over time and temperature and ensuring long-term measurement stability are substantial challenges. Moreover, ensuring bias currents don’t interfere with measurements made on high-impedance sensors can also be difficult. Lastly, many op-amps’ bandwidth constraints limit the signal frequencies that can be captured and the op-amps’ compatibility for many real-world applications. As such, there is a significant demand for op-amp technology that doesn’t compromise on noise, precision, or speed and can address these challenges without requiring designers to spend time and resources on workarounds for op-amp performance trade-offs.

Built For Precision Systems

Recognizing this demand, Analog Devices developed the ADA4620 family of 36V high-precision, low-noise JFET op-amps, available in single- and dual-channel variants. These op-amps feature rail-to-rail output with 16.5MHz bandwidth, plus very low offset voltage and offset voltage drift, input bias current, 1/f noise, voltage noise density (Figure 1), total harmonic distortion (THD), and supply current. Furthermore, they feature a high slew rate of 32V/μs with a wide power supply range of 4.5V to 36V for a single supply and ±2.25V to ±18V for a dual supply while exhibiting no phase reversal and absolute unity-gain stability.

Figure 1: Input voltage noise density versus frequency performance of the ADA4620 op-amps. (Source: Analog Devices)

These specifications mean that the ADA4620 family of op-amps is designed to meet the needs of applications requiring high DC precision, AC performance, low noise, and high speed with low power consumption. With this performance, the ADA4620 op-amps address common challenges in various instrumentation applications.

Electronic Test & Measurement

Several key performance areas of interest exist for electronic test and measurement (ETM) devices such as source measurement units (SMUs), power analyzers, and digital multimeters. These include baseline stability and measurement repeatability over measurement cycles, thermal shifts, and other environmental factors.

The ADA4620 family of op-amps offers extremely low input offset voltage, low input bias current, and minimal offset drift over temperature, helping ensure precision and repeatable performance. Other ETM considerations include the need for fast signal settling and low measurement latency. With a wide gain-bandwidth product (GBWP) and extremely fast slew rate, these op-amps are well suited to highly transient signal conditions. Moreover, ETM applications often suffer from distortions from common-mode transients, which is largely mitigated by the ADA4620’s wide input common-mode range (Figure 2).

Figure 2: A photodiode application diagram with key elements using the ADA4620 family of op-amps. (Source: Analog Devices)

Scientific Instrumentation

Op-amp performance is often a limiting factor for scientific instrumentation such as spectroscopy systems, pH meters, piezoelectric transducers, photodiode-based sensors, and load sensors. One of the top constraints for these applications is providing good signal integrity, even with high-impedance signal paths. The ADA4620’s low max input bias current, which is 50 percent lower than competitive devices, facilitates these signal path conditions.

Another concern is achieving high measurement resolution in very low-power analog front-ends. With minuscule 1/f noise and voltage noise, the ADA4620 devices are ideal for high resolution in low-level analog front-ends and low-noise, lab-grade sensors. These instruments also require measurement stability over time and through challenging environmental factors, and the ADA4620’s superior offset and drift performance meet these needs.

Field & Remote Sensing

Many field and remote sensing instruments must maintain low-power operation. The ADA4620’s low maximum supply current enables low-power operation over an extensive temperature range. The op-amp family’s wide-input, common-mode range also allows for sensor interfacing in electrically noisy or floating conditions.

Fast Prototyping

Some op-amp products require a substantial learning curve to even evaluate the device for an application. The Analog Devices EVAL-ADA4620-1 and EVAL-ADA4620-2 evaluation boards empower engineers to become familiar with and prototype a solution with minimal learning curve or setup effort. These evaluation boards support a range of applications, including active loop filters, trans-impedance amplifiers (TIAs), and charge amplifiers, while offering unpopulated pads for customization.

Conclusion

In precision instrumentation design, engineers may be forced to make trade-offs among accuracy, noise, speed, and power efficiency. As a result, they need components that minimize these compromises to build reliable systems that perform consistently in real-world conditions.

The ADA4620-1 and ADA4620-2 help engineers avoid compromises with op-amp performance. Whether incorporated into lab-grade measurement tools or remote scientific instruments, these op-amps offer high DC accuracy, low noise, efficient bandwidth-to-power performance, and robust operation across challenging conditions.

Jean-Jacques (JJ) DeLisle attended the Rochester Institute of Technology, where he graduated with a BS and MS degree in Electrical Engineering. Before completing his degree, JJ contracted as an IC layout and automated test design engineer for Synaptics Inc. Further pursuing his career, JJ moved to New York City, where he took on work as the Technical Engineering Editor for Microwaves & RF magazine. In the next phase of JJ’s career, he moved on to start his company, RFEMX, seeing a significant need in the industry for technically competent writers and objective industry experts. Progressing with that aim, JJ expanded his company’s scope and vision and started Information Exchange Services (IXS).