TI’s New SAR ADCs Beat Old Noise and Sampling Rate Challenges

June 21, 2021 by Antonio Anzaldua Jr.

TI extends its family of SAR ADCs, striving to beat old design challenges. How do these new family members stack up when compared to some competitors?

Industrial designs often involve many switching, monitoring, and power devices. For instance, devices used in power systems often deal with high volumes of data through voltage and current channels for multi-phase distribution networks. 

One key factor in allowing industrial designs to have efficient data acquisition is analog-to-digital converters (ADCs). 

Though there are various types of ADCs, one that plays into today's article topic is a successive approximation register (SAR) capable of precise convergence of continuous analog waveforms into digital output. 


A simplified SAR DAC block diagram. 

A simplified SAR DAC block diagram. 


Since power management is critical in power distribution systems, by adding an ADC to a complex system, the rate at which instances change voltages or current will be analyzed and monitored to prevent system failures. 

SAR ADCs can often add another layer of robustness with an improved signal resolution, extended battery life, and better system protection. 

Recently, Texas Instruments (TI) announced an extension of its high-speed data converter portfolio by adding eight SAR ADCs in 14, 16, and 18-bit resolutions. This article will discuss the new SAR ADCs, what design challenges these new members overcame for TI's family, and how these offerings compare to others in the industry.


Extending TI's SAR ADC Family

Engineers can typically reduce power up to 65% when designing high-speed digital control loops with a high dynamic range and low latency. However, how this is done can depend on the components used. 

When it comes to the ADC3660 portfolio, these new extensions claim to help designers reduce electrical component counts, thus increasing design flexibility. 

The ADC3660 has an overall power consumption of 94 mW per channel, which is just one interesting spec from this extension. Another is that, for simple thermal management, TI's newest option for 14-bit, ADC3541, offers 36 mW per channel, thus potentially extending battery life in power-sensitive applications such as GPS receivers. 

TI's ADC3683, on the other hand, is an 18-bit ADC that samples data at 65 MSPS, focusing on unwanted noise found in narrowband-frequency applications like portable defense radios, signal-to-noise ratio. The ADC3683 also enables oversampling, a technique used to clear harmonics out of the desired signal path. 


Block diagram for the ADC3683.

Block diagram for the ADC3683. Image used courtesy of Texas Instruments


TI's latest family of SAR ADCs aim to bring high sampling speeds while limiting electrical components needed, such as external amplifiers and driver circuits.

With this in mind, what design challenges is this new release overcoming for TI? 


Overcoming Previous Design Challenges 

In 2015, TI published an application report that discussed the design challenges for needing external driver circuits and amplifiers for SAR ADC architectures to filter noise and establish internal parameters. 

What was learned was that many tradeoffs needed to occur to improve TI's 1st-generation SAR ADCs, one of them being a reduction in the sampling rate to increase data acquisition time to 248.3 μs. The sampling rate ends up decreasing from 10 to 4 KSPS (kilo samples per second). The latest model of SAR ADC, the ADC3660, states it can process data at 65 MSPS (million samples per second) and 31 MSPS in bypass mode. 

Another challenge designers had to overcome in the past was choosing from solid noise performance or low power consumption. TI's latest family of SAR ADCs claims to bypass this old tradeoff by having an improved noise spectral density of internal decimation filter that boosts noise performances in narrowband-frequency applications, all while operating at 94 mW per channel (dual-channel). 

Despite the advancements and these new releases overcoming previous design challenges, how do these compare to similar products?


TI vs. Analog Devices vs. Maxim Integrated

One competitor that makes SAR ADCs is Maxim Integrated. 

Maxim has built a comprehensive platform of technologies from sensor platforms to power management systems over the last two decades. What separates TI's ADC from Maxim Integrated is the SAR architecture; Maxim's MAX11904 is a 20-bit resolution, 1 MSPS, SAR ADC with internal reference buffers, digital-to-analog converter (DAC). 


Equipped with a patented charge-pump architecture that allows for direct sampling of high-impedance sources.

Equipped with a patented charge-pump architecture that allows for direct sampling of high-impedance sources. Image used courtesy of Maxim Integrated


Maxim states that SAR ADCs can provide a system with low power consumption, high resolution, and precise data acquisition without facing limitations in the sampling rate. 

Similar to Maxim Integrated, Analog Devices (ADI) has a SAR ADC solution with an internal reference buffer for added design flexibility. 

The AD7960 from ADI, on the other hand, is an 18-bit, 5 MSPS PULSAR differential ADC with a power dissipation of 39 mW per channel. By activating the internal reference buffer, this solution could consume an additional 18 mW of power.


Block diagram for the AD7960. Image used courtesy of Analog Devices


ADI's offering also provides designers with full access to a precision ADC driver tool. This web application tool can run simulations of projected performances, distortions, design tradeoffs, and driver selection. 

Both Maxim and ADI focused on resolution with their high speed, multiplexed ADCs well suited for medical instrumentation applications.
Finally, when placing Maxim Integrated and ADI up against Texas Instruments, TI's SAR ADC appears to hold the advantage. 

TI's solution features a low-noise setup that can clear harmonics, removing the need for an external filter which saves on costs. Also, with the addition of the sampling rate for TI's ADC3660 being 65 MSPS, that gives TI an upper hand in highly intensive data acquisition applications. 



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