Texas Instruments ADS1298
Although its data sheet calls it an analog front end (AFE), the Texas Instruments ADS1298 provides far more application-oriented functionality than simple signal conditioning. It’s intended for dedicated heart and brain-wave monitors across a product range from mid-price-portable to the high end.
The chip integrates eight low-noise programmable gain amplifiers (PGAs) and eight high-resolution, simultaneous sampling analog-to-digital converters (ADCs), along with an oscillator and a voltage reference. Circuitry that customizes the device for medical instrumentation comprises an amplifier for right-leg drive and other amplifiers for Wilson Center Terminals (WCTs) and Goldberger Terminals (GCTs). If the instrument is to be used with external respiration circuitry, the ADS1298 can supply the required clocking signals.
The ADS1298 was developed to streamline instrument design. It can detect pacing pulses generated by a cardiac pacemaker within an ECG signal. It also can tell and report whenever any sensor lead is not properly attached to the patient. Other features include its low power consumption (1 mW/channel) and small footprint. It comes in either an 8- by 8-mm, 64-pin, ball-grid array (BGA) or a slightly larger thin quad flat-pack (TQFP), but there’s a significant further space savings in terms of external components.
In electrocardiogram (ECG) and electroencephalogram (EEG) equipment, “right-leg drive” refers to the practices associated with using the electrode on the patient’s right leg in common-mode interference rejection schemes. WCTs and GCTs are common approaches to minimizing common-mode interference.
The ADS1298 will be followed by four- and six-channel versions that will facilitate the design of sports and fitness monitors, fetal heartbeat monitors, and automated external defibrillators. To help engineers design products using the ADS1298 and these subsequent devices, TI offers an evaluation kit, the ADS1298 EVM.
On the digital side, the ECG Medical Development Kit, based on the C5505 DSP, accelerates the development of low-power patient monitoring applications. To get designers up to speed on medical applications, a Medical Applications Guide for Patient Monitoring, Diagnostics and Therapy can be downloaded from www.ti.com/diagnostic-pr.
The ADS1298 costs $23.95 in 1000-unit quantities.