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Op amps enable accurate medical devices

Posted: 11 Nov 2009 ?? ?Print Version ?Bookmark and Share

Keywords:operational amplifier? portable medical device? analog?

MAX9617/8 op amps

Maxim Integrated Products has released MAX9617 and MAX9618 operational amplifiers manufactured using BiCMOS process technology with patent-pending design architectures. The zero-drift, rail-to-rail op amps enable a new generation of portable medical devices. Packaged in 6-pin SC70 (single) and 8-pin SC70 (dual) packages, the devices claim outstanding precision and low-noise performance and very small solution size.

Designed to operate from 1.8V to 5.5V supplies, the MAX9617/MAX9618 are suitable for a wide variety of portable medical applications in which high accuracy and low quiescent current are critical. They are also well-suited for industrial applications, such as loop-powered systems, that require a combination of low power and precision.

Advances in medical technology, along with rising healthcare costs, are propelling a move from clinical to outsourced care. From pulse oximetry to ECG imaging, the point of diagnosis is shifting from clinical labs to doctors' offices to homes. Driven by these tailwinds, the home medical market is expected to grow with a 9 percent CAGR over the next five years, building upon a $15 billion electronic spend in 2009.

System designers face the difficult task of scaling equipment that typically weighs upwards of 50 pounds into portable form factors that weigh under 10 pounds. They must also reduce equipment costs to allow dispersed deployment within the field, while minimizing power consumption to enable battery operation. And, because medical equipment comprises life-critical applications, designers must meet these requirements without compromising performance.

Thus, operational amplifiers that deliver precision and low-noise performance are key components in sensitive medical equipment. Electrocardiograms, for example, must be able to measure electrical signals generated by the heart through electrodes placed on the skin. The analog front-end needs to isolate these extremely small signals (0.1mV to 6mV) from an electrically noisy corporeal environment, which is typically characterized by a 300mV DC offset component and 1.5V common-mode component. Additionally, the low-frequency region of interest (0.05Hz to 150Hz) is susceptible to noise from power lines (50Hz) and other sources of EMI.

Since the front-stage amplifier must boost the biological signal several thousand times for display on a monitor, the amplifier must have a very high CMRR; ultralow input-offset voltage, bias current and input-voltage noise; as well as minimal 1/f noise.

In addition, Maxim's patent-pending autozero technique enables the MAX9617/MAX9618 to meet all of these performance requirements while minimizing power consumption and footprint for portable medical applications. This patent-pending technology achieves both a 10?V (max) input-offset voltage and an input-voltage noise of 1?VP-P from 0.1Hz to 10Hz. Designed to have minimal 1/f noise, the devices facilitate accurate low-frequency measurements and allow for optimization of active filter designs. Moreover, the precision of the MAX9617/MAX9618 will not degrade with time and temperature, as they both feature very low (5nV/C, typ) input-offset-voltage drift.

The devices consume a mere 59?A of quiescent current per amplifier to extend battery life in portable equipment. Competing "zero drift" operational amplifiers with bandwidth greater than or equal to 1MHz typically consume 10x more quiescent current. The industry-leading speed-to-power ratio of the MAX9617/MAX9618 allows use in a wide range of applications without compromising customer power budgets.

The MAX9617/MAX9618 are fully specified for operation over the -40C to +125C automotive temperature range. Prices start at $0.85 (1,000-up, FOB USA).

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