The Design Of Standard 12-Lead ECG DAQ Instrument Based On USB 2.0

The cardiopathy is one of the most dangerous diseases which threaten the human health, so it is very significant to develop a high performance heart examining system which can diagnose the heart trouble and cure it in time. The electrocardiogram (ECG) is a routine checking means to heart diseases, and to sample the standard 12-lead ECG signals and interface to host easily and rapidly is the future of the electrocardiograph. This paper is to introduce the development of the standard 12-lead ECG data acquisition instrument, meanly about the design of hardware and software, with the USB 2.0 as the interface to communicate with the PC. The instrument is an electrocardiograph that can synchronously sample the standard 12-lead ECG signals easily and rapidly with high resolution, and it is the hardware part of the ECG diagnosing system. It can be divided into three parts: pre-amplifier, A/D, and USB controller. The pre-amplifier segment is meanly to amplify and filter the ECG signals. This part is very important in the designing of electrocardiograph, because the ECG signals are feeble, and always include kinds of interferes. The aim of this part is to reduce the undesired components and amplify the tiny signals to the allowing input ranges of the ADCs. Analog-to-Digital converter's function is to convert the analog signal to digital code. Here employs the Sigma-Delta ADC, for it makes use of many technics like over-sampling, noise-shaping, digital decimation filter, which can allow it to realize the high resolution with low cost, and also this kind of ADC is easily to be integrated with digital-signal-processing system in one chip, and is not need the sample-hold circuits, and has lower requirement to the input filter, etc. Three AD7716 are used here so as to contribute a 12-channel DAQ system, and the resolution is 22-bit. The USB physical interconnect is a tiered star topology, and it has the features such as hot plug, high speed, plug and plug, independent power, excellent compatibility. This paper takes the Cypress'CY7C68013 as the USB controller, and the company provides a full development kit, including hardware designing, firmware and driver developing, which accelerates the soft-and hardware development. USB 2.0 is used as the interface to PCs in this system for its convenience, and that it synchronously samples the standard 12-lead ECG signals permit the doctor to comprehend the heart status more completely and more thoroughly, and this is propitious to diagnose and inspect the heart diseases.