Advantages of a High Precision ADC in Space Applications

Main body and conclusion (LC)

The ISL71148 8-Channel SAR ADC

In high-reliability electronics utilised in space applications, measurement precision and resilience are critical. From measuring system voltages and temperatures to precise motor control it is imperative to have a fully accurate measurement. Many electronic devices require closely controlled supply voltages that need to be monitored and adjusted. In addition, knowledge of the system temperature is important so that temperature compensation can be applied where necessary.

Another key area is precise motor control, where exact position and speed are of utmost importance. The ISL71148M, a radiation-tolerant 8-channel 14-bit 900/480ksps SAR ADC from Renesas, meets these challenges with cutting-edge performance. The ISL71148 offers many features and advantages that uniquely equip the part to handle these types of applications, setting it apart from competitors. In addition, the ISL71148 SAR ADC is offered in Radiation Tolerant and Radiation Hardened screening flows to suit different mission profiles.

Unmatched Precision and Speed

The ISL71148 excels in analog-to-digital conversion with 14-bit resolution, providing 4 times better measurement accuracy than competing 12-bit ADCs. This precision is essential for applications demanding high signal fidelity. The ISL71148 also offers a programmable gain amplifier (PGA) to further enhance system flexibility and performance. This PGA can be programmed with eight different gains values depending on the amount of gain required in the application. This PGA may also be bypassed depending on system needs.

High Throughput: Capable of 900ksps without the PGA and 480ksps with the PGA enabled, ensuring real-time data acquisition without latency. This allows the ISL71148 to quickly acquire the necessary telemetry data to allow for quick adjustments to be made by the system processor.
Superior Linearity: Differential Non-Linearity (DNL) of ±0.2 LSB and Integral Non-Linearity (INL) of ±0.4 LSB enhance accurate signal representation. The clarity and accuracy of the ISL71148 allows for tight control of system voltages and for accurate responses to changes in system temperature.
Low Noise Performance: Achieves an SNR of 83.2dBFS (PGA bypassed) and 77dBFS (PGA gain = 2), capturing even the smallest signals with precision. The low noise level of the ISL71148 allows for acquisition of incredibly small voltages that enable the system processor to have very precise control capabilities.

Advanced Functionalities

Unlike existing solutions in the marketplace, the ISL71148 integrates several innovative features to optimise performance and flexibility. This results in decreased system complexity while offering a reduced BOM. In addition, the overall size of the solution is reduced. These factors all combine to result in overall reduced system cost. The many integrated features of the ISL71148 include:

Rad Tolerant 8-Channel SAR ADC Evaluation Board - ISL71148MNZEV1

ISL71148MNZEV1 - Rad Tolerant 8-Channel SAR ADC Evaluation Board

ISL71148 Functional Block Diagram

Buffered Differential Input Channels: Featuring an 8-to-1 multiplexer with high input impedance (>1GΩ) and low capacitance (<5pF), minimizing loading effects. The ISL71148 essentially presents no loading which enables data acquisition while being virtually invisible. The system BOM cost is lowered with the integrated multiplexer that allows the internal ADC to be multiplexed to eight different signals for monitoring.
Programmable Gain Amplifier (PGA): Selectable gains (1, 2, 3, 4, 6, 8, 12 and 16), with a bypass option for maximum sampling rates. The PGA provides unparalleled flexibility to meet many different use case requirements enabling acquisition of signals across a wide range of input voltages.
Input Channel Sequencer (SCAN): Enables automated cycling through channels, ideal for multi-channel data acquisition. This feature enables the user to further reduce system complexity by automatically cycling through all eight channels sequentially eliminating the need to externally control channel selection if desired.
Low Power Mode: Reduces power dissipation at lower sample rates, enhancing energy efficiency. In applications where power requirements are very stringent this mode can be used to reduce the power consumption of the ISL71148 to be reduced by nearly 30% conserving critical battery power until the next charging cycle.
High-Speed SPI Interface: Operates between 2.2V to 3.6V, ensuring seamless digital system integration. The SPI interface operates up to 50MHz allowing for quick offloading of the acquired data to the system processor. The interface supports both 2.5V and 3.3V logic levels for compatibility with many different processors and/or FPGAs.
Digital Clamping: Prevents output code rollover, maintaining data integrity. The output data is digitally clamped at +/- full scale to preserve proper data scaling and avoid any data processing issues.

Radiation Tolerance for Harsh Environments

Designed for extreme conditions such as space and high-altitude applications, the ISL71148 is suited for even the most extreme environments in space applications. It is suitable for applications ranging from LEO (low earth orbit) to GEO (geostationary orbit) and beyond.

For LEO applications the ISL71148M is offered in the Renesas radiation tolerant screening flow:

Total Ionizing Dose (TID): Available in 30krad(Si) and 50krad(Si) variants for moderate radiation environments.
Single Event Effects (SEE) Protection: Characterized up to an LET of 43MeV to withstand up to AVCC = 6.2V, DVCC = 4.6V, and VREF = 3.6V, with a SEFI cross-section <3.1μm².

For GEO applications and beyond the ISL71148SLHM is offered in the Renesas radiation hardened screening flow:

Total Ionizing Dose (TID): Qualified to 75krad(Si) for radiation-heavy environments.
Single Event Effects (SEE) Protection: Characterized up to an LET of 86 MeV to withstand up to AVCC = 6.2V, DVCC = 4.6V, and VREF = 3.6V, with a SEFI cross-section <3.1μm².

Additionally, for the case of both product variants, the ISL71148 offers incredible SET (single even transient) performance. No observable transients were observed lasting longer than three consecutive samples with greater than 99% of observed SETs under beam lasting for only a single sample.

Competitive Advantages

In summary, the ISL71148 products surpass competing ADCs on many fronts ranging from resolution to solution size, cost and radiation performance. The ISL71148 products stand head and shoulders above the competing products in the marketplace. These competitive advantages include:

Superior Accuracy: 14-bit resolution ensures higher precision than 12-bit alternatives. This results is 4x the measurement accuracy for more precise data acquisition which enables very tight system control.
Integrated Design: Buffered inputs and PGA eliminate external components, saving space and cost. The integrated features of the ISL71148 reduce system complexity as well as design and BOM costs while easing system design constraints.
SEE Mitigation: The ISL71148 internally resets after each sample enhancing its robustness when exposed to heavy ions. When impacted it quickly recovers allowing it to have extremely minimal impacts on system performance and data acquisition.
Flexible Operation: The available PGA, low-power mode, and input channel sequencer allow for a wide range of configurability in a multitude of applications.
Robust Temperature Performance: The ISL71148 operates from -55°C to +125°C, ensuring reliability in extreme conditions presented in space applications.
Seamless System Integration: The digital interface supports both 2.5V and 3.3V logic levels maximizing interoperability and simplifying connectivity with various processers and FPGA. In addition, the digitised data is available with no conversion latency allowing for fast and accurate data acquisition.

ISL71148VMREFEV1Z Voltage Monitor Reference Design Board

Ideal Applications

The ISL71148M is well-suited for many different types of space applications including but not limited to the following:

Precision signal processing such as satellite telemetry and motor control
Propulsion and payload systems as well as engine control

Conclusion

The ISL71148 is a game-changer in precision data acquisition, offering unparalleled accuracy, speed, and flexibility. Its radiation performance and robust design make it the optimal choice for high-reliability applications in the space environment. By utilising the ISL71148, designers can achieve exceptional performance while ensuring system simplicity and reliability in the most demanding environments.

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About Author

Jonathan Harris

Jonathan Harris is a Senior Staff Applications Engineer, Space and Hi-Rel Products at Renesas Electronics with over 20 years of experience in various applications engineering roles. Jonathan currently manages a team of three engineers and often collaborates with the Renesas marketing and design team to use customer feedback to improve current products.