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Instrumentation amps offer autozeroing architecture

Posted: 27 Dec 2007 ?? ?Print Version ?Bookmark and Share

Keywords:instrumentation amplifiers? spread-spectrum autozeroing?


Maxim Integrated Products has introduced the MAX4208/MAX4209H instrumentation amplifiers that feature its patented current-feedback architecture, a spread-spectrum autozeroing technique.

The autozeroing technology constantly measures and corrects the input offset voltage, thereby eliminating drift over time and temperature. The input offset voltage is 20?V (max) at 25C, and 40?V (max) over the 40C to 125C temperature range. The technology's compact design allows the MAX4208/MAX4209H to fit in a small, 3mm x 5mm ?MAX package, making them well suited for use in a wide range of applications. The amplifiers can monitor the low-voltage, power-supply currents of the core, ASIC and microprocessor in laptop computers. The amplifiers are also used in automotive, industrial, and medical instrumentation.

Smart design
The MAX4208/MAX4209H feature an innovative, two-transconductance-amplifier architecture. This indirect current-feedback architecture allows customers to use the full dynamic range of input differential signals, even when the common-mode voltages are close to, or below, ground. This true low-side sensing capability is not offered by the common three-operational-amplifier approach.

The MAX4208/MAX4209H offer true ground sensing and an input common-mode voltage range of -0.1V to VDD - 1.3V. CMRR is guaranteed to be at least 106dB.

The devices' input stage uses CMOS transistors with 1pA (typ) input bias current. Input offset voltage is 20?V (max) at 25C, 30?V (max) at 85C, and 40?V (max) over the 40C to 125C temperature range.

The MAX4208 features an adjustable gain, with the gain set by the ratio of two external resistors (G = 1 + R2/R1). The MAX4209H uses internal laser-trimmed resistors to set a fixed gain of 100x. The MAX4209H has a maximum gain error of 0.25 percent at 25C, 0.3 percent up to 85C, and 0.35 percent over the entire -40C to 125C temperature range.

The MAX4208/MAX4209H also include an autozero reference-buffer amplifier, which allows the output to be level-shifted to VDD/2 using a simple resistor-divider or an external reference input with minimum loading error. This buffer increases system accuracy and is useful for bipolar signals in single-supply applications. The high-impedance inputs are optimized for small-signal differential voltages (100mV). All devices operate from a single 2.85V to 5.5V supply (or 1.425V to 2.75V dual supplies) with ground-sensing capability and ultra-low, 1pA (typ) CMOS-input bias currents.

Samples of the MAX4208/MAX4209H are available now. The devices are priced at $1.65 for 1,000-units.

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