“With the increased need for monitoring of many chronic diseases and physical conditions, the use of patient monitoring devices is rapidly expanding as they are critical to speeding healing, avoiding complications and maintaining optimal health. A typical patient monitoring device interconnection system transfers data (sometimes including high-resolution images), power, and control signals within and between devices. Designers of these systems must contend with numerous and often conflicting challenges, including smaller form factors, greater feature sets, and faster data rates that require high signal integrity (SI) and smooth data transfer.
Author: Jeff Shepard
With the increased need for monitoring of many chronic diseases and physical conditions, the use of patient monitoring devices is rapidly expanding as they are critical to speeding healing, avoiding complications and maintaining optimal health. A typical patient monitoring device interconnection system transfers data (sometimes including high-resolution images), power, and control signals within and between devices. Designers of these systems must contend with numerous and often conflicting challenges, including smaller form factors, greater feature sets, and faster data rates that require high signal integrity (SI) and smooth data transfer.
At the same time, these devices must be comfortable for the patient and, despite the monitor’s inherent complexity and criticality of its functionality, be easy to use (when appropriate) for both the caregiver and the patient. Using bulky, inappropriate, or poorly designed connectors or interconnects can defeat these goals and add unnecessary costs.
To meet the requirements of these applications, the market provides designers with a number of increasingly sophisticated connector and interconnect device options. For example, depending on the needs of a specific application, designers can choose flat-flex (FPC) high-density connectors for low-cost automated assembly, or flexible printed cables with fine center-to-center spacing where wire-to-board solutions are impractical ( FPC), or choose a USB Type-C® connector that provides a compact, easy-to-use, high-speed connection.
This article briefly reviews the interconnection requirements of patient monitoring devices, exploring the connections within the device and between the device and the outside world. Molex’s FFC, FPC, and USB Type-C connectors are then presented with examples, discussing their key features and benefits, and how to apply them correctly.
Board-to-Board Interconnect Requirements
The combination of FFC and FPC can support designers’ needs for high-density and high-speed board-to-board interconnection systems for patient monitoring equipment. Some of these connectors are available for manual and robotic assembly operations and feature single-step mating with an automatic locking mechanism (Figure 1).
Figure 1: FFC and FPC connectors are available for manual and robotic assembly operations and feature single-step mating capabilities with an automatic locking mechanism. (Image credit: Digi-Key Electronics)
FFC board-to-board connectors can be used to support data rates up to 40 gigahertz (GHz) and provide up to 80 connections in multiple low-profile orientations, including right-angle and vertical orientations, enabling design flexibility choose. The connection pitch can be less than one millimeter (mm) to support narrow package designs. Zero Insertion Force (ZIF) and non-ZIF designs are available to meet specific application needs.
Some FFCs are specified for temperatures up to 150 degrees Celsius (°C) and can be used in a variety of cabling options, including general-purpose FFC cables, locking FFC cables, or custom FFC cables. These connectors typically accept standard or shielded FFCs, and ground terminations 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 ground terminals.
Connect patient monitors to the outside world
Patient monitoring is critical for caregivers because it helps them understand how the body responds to therapies that lessen or repair the effects of disease or other bodily ailments. This often requires sending the monitored data to a device other than the monitoring device.
The USB Type-C connector can be the best choice for connecting patient monitoring equipment to external devices such as HDMI displays and data storage systems. These connectors feature a symmetrical and reversible pin layout for ease of use and flexibility as they can be connected in any orientation (Figure 2).
Figure 2: The USB Type-C connector has a symmetrical and reversible pinout for ease of use and flexibility. (Image credit: Digi-Key Electronics)
Implementation of the latest USB4 protocol must use a USB Type-C connector. Based on the Thunderbolt 3 interface, USB4 allows DisplayPort and PCI Express (PCIe) data to be tunneled and supports a nominal data rate of 20 gigabits per second (Gbits/s) and is scalable to 40 Gbits/s. With the ability for multiple end device types to dynamically share a single high-speed link, USB4 can optimize data transfer by type and application. Therefore, the nominal 20 Gbit/s data rate when sending mixed data can result in higher effective throughput than USB 3.2 when tunneling is used.
The USB Power Delivery (PD) protocol provides up to 20 volts, 5 amps (A) and 100 watts for charging and other uses, including expanding data transfer capabilities. Compared to the 1.8 A charging capability of Micro USB 2.0, USB Type-C PD can reduce battery charging time by 40% to 64%. The intelligent and flexible system-level power management of USB PD supports bidirectional power supply, which can switch directions in real-time, making it possible for Type-C to support other standards such as DisplayPort, HDMI or PCIe.
Fast Role Swap (FRS) is an improvement in the latest version of the USB Type-C PD specification. Designers can use FRS to reduce the risk of data loss and maintain the signal integrity of USB peripherals such as patient monitoring equipment if the power cord is accidentally removed from the hub or cradle. FRS is implemented in 150 microseconds (μs), allowing the battery to be the source and the other devices to be the drain and keep running uninterrupted. Data communication continues uninterrupted in a single direction, keeping the system running and preventing failures even if the power direction is reversed.
Another enhancement to USB PD performance under USB4 is Programmable Power Supply (PPS) capability. PPS enables small step regulation of voltage and current. If a power outlet is connected to a PPS-capable power source, it can request that the power delivered by the power source be changed. PPS enables fast charging of lithium-ion batteries, improving the power efficiency of the overall system, reducing thermal loads, and enabling higher system packing densities.
Board-to-Board Connectors for Medical Monitoring Equipment
As mentioned above, the combination of FFC and FPC addresses the needs of patient monitoring device designers for high-density and high-speed board-to-board interconnect systems, while supporting manual or robotic assembly. Model 0541324062 in Molex’s Easy-On FFC/FPC connector family is a good example. The connector has 40 positions, gold-plated contacts, and 0.50 millimeter (mm) pitch (Figure 3).
Figure 3: The Molex Model 0541324062 Easy-On FFC/FPC connector has 40 positions, gold plated contacts, and 0.50 millimeter (mm) pitch. (Image credit: Molex)
The 0541324062 model supports data rates up to 10 Gbits/s. Full cable insertion and secure mating with active inertia lock. A cable retention force of 20 Newtons (N) ensures shock and vibration resistance. Robust solder lugs bring retention and strain relief to the printed circuit board.
Molex’s Premo-Flex Model 0151660431 FFC patch cords have a 0.50 mm pitch and a 102.00 mm length (Figure 4), when used with the Model 541324062 Easy-On FFC/FPC Connector, to align with the connector’s 40 pin positions patch. This board-to-board interconnect system can help designers address challenges in applications where space is constrained or difficult to reach.
Figure 4: Molex’s 0151660431 0.50 mm pitch Premo-Flex FFC jumper has 40 positions and is 102.00 mm long. (Image credit: Molex)
Molex offers Premo-Flex patch cords in a variety of cable lengths, circuit sizes, pitches and thicknesses. These durable, ultra-flexible cables are rated to 105°C and have a flex life of 900,000 cycles compared to 6,000 cycles for standard patch cords.
Note that when connecting or disconnecting the FFC jumper from the Easy-On FFC/FPC connector, you must ensure that all connections are de-energized to avoid sparks that could damage the contacts. In addition, when opening or closing the lock, you should apply force on both sides of the lock at the same time. Applying force to only one side may damage the connector. Finally, when inserting the flex cable into the connector, there shouldn’t be any pull or tension on the cable. Otherwise, the locker may not lock properly, the cable may be damaged, or the line may be cut.
High-speed external connections
Molex USB Type-C series connectors such as the 1054500101 can support trouble-free patient monitoring data transfer and high signal integrity while providing power to the device (Figure 5). Molex uses three insert molding processes in its USB Type-C connectors, making the mating tongues a single piece and minimizing water ingress. With three additional insert molding processes, the risk of terminal pull-out or bending is minimized, resulting in higher mechanical durability and electrical reliability. These connectors provide a durable solution, rated to 10,000 mating cycles, to withstand improper insertion attempts and other abuse.
Figure 5: A USB Type-C connector like the 1054500101 can support trouble-free data transfer and provide power to medical monitoring equipment. (Image credit: Molex)
These high-performance connectors have the following characteristics:
・ Up to 40 Gbit/s data rate to support high-speed network applications
・ Supports 4K resolution high-quality monitors
・Shield providing EMI/RFI protection
・ Prevent electrical shorts during mating by using tape plugs between the housing and the housing.
・ Stable electrical performance, supporting higher current capacity and minimal temperature rise
The increased power capacity of the USB Type-C connector enables smaller pin spacing, which means designers need to be aware of potential safety and fire hazards in the event of thermal runaway. Under normal circumstances, the USB PD power rules ensure safe operation. However, damage to the connector or cable can result in unsafe operation. Overcurrent and overtemperature protection devices are often included in the design of USB Type-C connectors and cables to reduce the possibility of thermal runaway.
The SuperSpeed transmission differential pair in a USB Type-C cable has a differential impedance of 90 ohms (Ω). Designs using alternate mode must also be able to handle 90 Ω.
As the need for patient monitoring increases, designers of such systems require connectors and associated interconnecting cables and patch cords that can reliably transmit multiple types of high-speed data as well as power and control signals to and from the patient send out. These connections must often be made in tight spaces with minimal cost, while ensuring ease of use and minimal impact on patient comfort.
As mentioned above, the advent of FFC, FPC, and USB Type-C connectors addresses these challenges with efficient assembly capabilities, high signal integrity, and greater ease of use. With the right combination of these connectors and interconnects, designers can address the inherent complexities of patient monitoring, from electrical performance to quality of care.