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High Speed And Safety Reinforced Digital Isolator For Endoscope And Medical Imaging Applications White Paper

1st July 2013

Avago Technologies

ES Admin

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Whitepaper

Patient contacts in medical devices must be isolated from ac mains to protect the patient from hazardous voltage shocks. In medical imaging devices, large quantities of video imaging data need to be transferred from image sensor to image processor while maintaining high levels of electrical isolation so the sensor won’t shock the patient. By Zhang Bin and Harold Tisbe of Avago Technologies.

The high-speed digital data transmission channels between the sensor and image processor require high-levels of isolation while transferring data at up to 100Mbaud for real-time displays.

The combination of high speed and stringent safety requirements presents signifi cant challenges to isolation design and often resulted in expensive solution, e.g. fibre optics. With latest transformer on flex technology developed by Avago Technologies cost-effective isolation solutions meeting both high speed and medical safety requirements are now available.

Using magnetic coupling through a thick insulation barrier, the isolators enable high speed transmissions without compromise in isolation performance. These isolators consume low power even at high data rates, yet provide excellent transient immunity performance in compact surface mount packages. The devices are qualified to a maximum propagation delay of 36 ns.

Overview Of Endoscope System Design And Isolation Requirements

Shown in Figure 1 is the schematic block diagram of an endoscope where a light guide and a CCD image sensor are housed in a flex tube that is introduced into a patient’s body. Video signals of what the sensor captures are transmitted to the CCD analog-front-end circuit where they are digitized and sent on to an image processor for image reconstruction. Typically, digitized data from the AFE is 16 bits wide and clocked out at the rate of up to 50 MHz or more, depending on image size and resolution requirements.

The control signals configuring ADC behaviour and timing units are of lower speed in nature. However due to the needs for fast throughput and the use of a high-speed clock, it is important that the insertion of digital isolators does not introduce additional pulse-width distortion. Channel-to-channel propagation delay skew should also be kept to a minimum to ensure synchronous data transfer at high data rates. Given large number of data and control channels it is most desirable that more channels could be integrated into single package for space saving.

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