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Op amps deliver high precision to portable medical apps

Posted: 11 Nov 2009     Print Version  Bookmark and Share

Keywords:operational amplifier  portable medical device  analogue 

MAX9617/8 op amps

The MAX9617/MAX9618 from Maxim Integrated Products are zero-drift, rail-to-rail operational amplifiers using BiCMOS process technology and patent-pending design architectures. These devices deliver outstanding precision and low-noise performance while minimising solution size. Additionally, they also offer best-in-class power consumption to enable a new generation of portable medical devices. They are available as 6-pin SC70 (single) and 8-pin SC70 (dual)

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 per cent CAGR over the next five years, building upon a Rs. 73,223.13 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 less than 10 pounds. They must also reduce equipment costs to allow dispersed deployment within the field, while minimising 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 analogue front-end needs to isolate these extremely small signals (0.1mV to 6mV) from an electrically noisy corporeal environment, which is typically characterised 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; ultra low 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 minimising power consumption and footprint for portable medical applications. This patent-pending technology achieves both a 10µV (max) input-offset voltage and an input-voltage noise of 1µVP-P from 0.1Hz to 10Hz. Designed to have minimal 1/f noise, the devices facilitate accurate low-frequency measurements and allow for optimisation 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, type) input-offset-voltage drift.

The devices consume a mere 59µ 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 is fully specified for operation over the -40°C to + 125°C automotive temperature range. Prices start at Rs.41.49 (1,000-up, FOB USA).

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