Use Dense and Flexible Interconnects to Design Compact, High Performance Patient Monitoring Devices

Patient monitoring of many chronic diseases and medical conditions is rapidly expanding, and it can be crucial to accelerating healing, avoiding complications, and maintaining optimal health. The typical patient monitoring device interconnection systems carry data (sometimes including high-resolution images), power, and control signals within as well as to and from the device. Designers of these systems must contend with numerous, and often conflicting, challenges including smaller form factors, more feature sets, and faster data rates that demand high signal integrity (SI) and smooth data transfers.

At the same time, the devices must be comfortable for patients, and easy to use for both healthcare professionals and patients (where appropriate) despite the inherent complexities of the monitors and the critical nature of their functions. Using a bulky, inappropriate, or poorly designed connector or interconnect can undermine these goals and add unnecessary cost.

To address the demands of these applications, designers have a number of increasingly refined connectors and interconnects to choose from. For example, depending on the demands of the specific application, designers can choose flat flex (FFC) high-density connectors for low-cost automated assembly, flexible printed cables (FPCs) with small centerline spacing where wire-to-board solutions are impractical, or USB Type-C® connectors that provide compact, easy-to-use, high-speed connections.

This article briefly reviews the interconnect needs of patient monitoring devices, looking at connections within the devices, and between the devices and the outside world. It will then introduce examples of FFC, FPC, and USB Type-C connectors from Molex, identifying key features and benefits as well as their correct application.

Board-to-board interconnects needs

FFCs combined with FPCs can support the needs designers have for high-density and high-speed board-to-board interconnect systems for patient monitoring devices. Some of these connectors can be used in both manual and robotic assembly operations, and feature single-step mating with an auto-lock mechanism (Figure 1).

Use Dense and Flexible Interconnects to Design Compact, High Performance Patient Monitoring DevicesFigure 1: FFCs and FPCs can be used in both manual and robotic assembly operations and feature single-step mating with an auto-lock mechanism. (Image source: Digi-Key Electronics)

FFC board-to-board connectors can be used to support data rates up to 40 gigahertz (GHz) and can provide up to 80 connections in several low profile orientations, including right angle and vertical to provide flexible design options. Connection pitches can be less than one millimeter (mm) to support tight packaging designs. Zero insertion force (ZIF) and non-ZIF designs are available to meet the needs of specific applications.

Some FFCs are specified for temperatures up to 150 degrees Celsius (°C), and they are designed for use with a variety of cabling options including generic FFC cables, locking FFC cables, or custom FFC cables. These connectors can often accept standard or shielded FFCs, and the grounding terminals support the needs of high-speed protocols such as low-voltage differential signaling (LVDS). For maximum performance, shielded cables should be used with connectors that have grounded terminals.

Connecting patient monitors to the outside world

Patient monitoring is crucial to enable caregivers to understand how the body is responding to therapies to mitigate or repair the effects of a disease or other physical ailment. That often requires getting the monitored data to equipment outside of the monitoring device.

USB Type-C connectors can be a great choice for connecting patient monitoring devices to external equipment such as HDMI monitors and data storage systems. These connectors have a symmetrical and reversible pinout that supports ease of use and flexibility as they can be connected in either orientation (Figure 2).

Use Dense and Flexible Interconnects to Design Compact, High Performance Patient Monitoring DevicesFigure 2: USB Type-C connectors have a symmetrical and reversible pinout that supports ease of use and flexibility. (Image source: Digi-Key Electronics)

USB Type-C connectors are required to implement the latest USB4 protocols. USB4 is based on the Thunderbolt 3 interface, allows tunneling of DisplayPort and PCI Express (PCIe) data, and supports a nominal data rate of 20 gigabits per second (Gbits/s) that can be extended up to 40 Gbits/s. USB4 includes the ability for multiple end device types to dynamically share a single high-speed link that optimizes the transfer of data by type and application. As a result, when tunneling is employed, the nominal 20 Gbit/s data rate can result in higher effective throughput when sending mixed data, compared with USB 3.2.

The USB Power Delivery (PD) protocol provides up to 20 volts, 5 amperes (A), and 100 watts for charging and other uses, including expanded data transfer capabilities. USB Type-C PD can reduce battery charging time by 40% to 64%, compared with the 1.8 A charging capacity of micro USB 2.0. The intelligent and flexible system level power management capabilities of USB PD support bidirectional power that can switch direction in real-time and makes possible Type-C support for other standards such as DisplayPort, HDMI, or PCIe.

Fast role swap (FRS) is an enhancement in the latest version of the USB Type-C PD specification. Designers can use FRS to lower the risk of data loss and preserve SI in USB peripherals, such as patient monitoring devices, in the event of unexpected removal of a power cable from a hub or dock. FRS is implemented within 150 microseconds (µs), enabling the battery to become the source and the other device to become the sink, maintaining uninterrupted operation. Data communication continues in a single direction without interruption, preserving system operation and preventing glitches, even though the power sourcing direction reverses.

Another enhancement to the performance of USB PD under USB4 is the programmable power supply (PPS) capability. PPS enables small step changes in voltage and current. If a power sink is connected to a PPS capable power source, it can request changes in the power delivered by the source. PPS can enable fast charging of lithium-ion batteries and improve overall system power efficiency, which reduces thermal loading and supports higher system packaging densities.

Board-to-board connector for medical monitoring devices

As noted above, FFCs combined with FPCs can support the need patient monitoring device designers have for high-density and high-speed board-to-board interconnect systems that can support either manual or robotic assembly. The model 0541324062 from Molex’s Easy-On FFC/FPC connector line is a good example. The connector has 40 positions with gold plating on a 0.50 millimeter (mm) pitch (Figure 3).

Use Dense and Flexible Interconnects to Design Compact, High Performance Patient Monitoring DevicesFigure 3: The model 0541324062 Easy-On FFC/FPC connector from Molex features 40 positions with gold plating on a 0.50 mm pitch. (Image source: Molex)

The model 0541324062 supports data rates up to 10 Gbits/s. Complete cable insertion and secure mating are implemented by the positive inertia lock. Shock and vibration resistance are ensured by the 20 Newton (N) cable retention force. Robust solder tabs supply printed circuit board retention and strain relief.

Used in conjunction with the model 541324062 Easy-On FFC/FPC connector, the model 0151660431 from Molex’s Premo-Flex FFC jumper line matches the connector’s 40 positions and 0.50 mm pitch and has a length of 102.00 mm (Figure 4). This board-to-board interconnection system can help designers solve challenges in space-constrained or hard-to-reach applications.

Use Dense and Flexible Interconnects to Design Compact, High Performance Patient Monitoring DevicesFigure 4: The 0151660431 0.50 mm pitch Premo-Flex FFC jumper from Molex has 40 positions and is 102.00 mm long. (Image source: Molex)

Molex offers Premo-Flex jumpers in a range of cable lengths, circuit sizes, pitches, and thicknesses. Rated to 105°C, these durable, ultra-flexible cables have a flex life of 900,000 cycles, compared with 6,000 cycles for standard jumpers.

Note that when connecting or disconnecting an FFC jumper from an Easy-On FFC/FPC connector, it is important to ensure that all connections are de-energized to avoid sparking that can damage the contacts. Also, when opening or closing the locking actuator, force should be applied to both sides of the actuator. Applying force to only one side could result in damage to the connector. Finally, when inserting the flex cable into the connector, there should be no pulling force or tension on the cable. Otherwise, the actuator may not lock properly, the cable may be damaged, or the traces cut.

High-speed external connections

Connectors such as the 1054500101 from Molex’s USB Type-C line can support glitchless patient monitoring data transfers and high SI while providing power to devices (Figure 5). Molex uses three insert molding processes in its USB Type-C connectors to make the mating tongue a single part and minimize water ingress. The risk of lifted or bent terminals is minimized by an additional three insert molding processes that result in higher mechanical durability and higher electrical reliability. These connectors provide a durable solution rated for 10,000 mating and unmating cycles that stands up to improper mating attempts and other abuse.

Use Dense and Flexible Interconnects to Design Compact, High Performance Patient Monitoring DevicesFigure 5: USB Type-C connectors such as the 1054500101 can support glitchless data transfers and provide power to medical monitoring devices. (Image source: Molex)

These high-performance connectors feature:

  • Up to 40 Gbit/s data rates to support high-speed network applications
  • Support of 4K resolution high-quality displays
  • Shielding to provide EMI/RFI protection
  • Prevention of electrical shorts during mating through the use of a mylar plug between the housing and shell
  • Stable electrical performance to support higher current capacity and minimal temperature increases

The increased power capacity and very tight pin spacing in USB Type-C connectors means that designers need to be aware of potential safety and fire hazards in the case of thermal runaway. Under normal conditions, the USB PD power rules ensure safe operation. However, damage to a connector or cable can lead to operation outside the safe area. Overcurrent and overtemperature protection devices are often included in the designs of USB Type-C connectors and cables to reduce the potential for thermal runaway.

The SuperSpeed transmit differential pairs in USB Type-C cables have a 90 ohm (Ω) differential impedance. Designs using an alternate mode must also be able to handle 90 Ω.

Conclusion

As the need for patient monitoring increases, designers of such systems need connectors and associated interconnect cabling and jumpers that can reliably transport multiple types of high-speed data, as well as power and control signals, both to and from the patient. The connections must often be made under tight space conditions at minimal cost, while also ensuring ease of use and with minimal impact on patient comfort.

As shown, FFCs, FPCs, and USB Type-C connectors have emerged to address these challenges through efficient assembly, high SI, and greater ease of use. Using the right combination of these connectors and interconnects, designers can address the inherent complexities of patient monitoring from electrical performance to quality of care.

Recommended reading

  1. Reliability is a Decisive Factor in Sensor-Based Medical Applications