Squeeze in more functionality with SIP technology

Nick Wood, President, Insight SiP explains how design engineers can use SIP (Systems-in-Package) to squeeze ever more functionality into ever smaller spaces.

System in Package is a way of providing a complete system in what looks externally like a single component (like a chip in a QFN package), but which inside are increasingly sophisticated systems, which can incorporate semiconductors, passives and RF components.

The Evolution of SIP

System- in- package techniques are not new, but initially were confined to specialist applications like military and aerospace. They first entered the mainstream in the memory market, and most “memory chips” in reality are SIPs with a number of stacked semiconductors.

However the technology has moved beyond SIPs for memory to far more complex solutions. The mobile phone is increasingly based on SIP technology, as the vendors struggle to meet the twin demands of slim elegant physical design and ever increasing technological sophistication.

Benefits

So what are the advantages of this approach? In comparison with traditional PCB modules, the components are smaller in all dimensions, without compromising performance, or adding to the price. And all the traditional advantages of the module approach remain equally true for a SIP module.

Module vs. Discrete solution

So what are the advantages – and disadvantages – of a module approach? Whether to take a discreet component or module approach is one of the key design decision when including an RF function such as Bluetooth Low Energy in a solution.

The disadvantage of the module approach is simple and comes down to one thing -the unit BOM cost will inevitably be higher. However, the advantages of the module approach are considerable. Firstly, engineer can complete forget about the analogue/RF parts of the design, making only a digital connection to the module. This lowers the time and cost of the design cycle, and perhaps more importantly reduces risk, as RF is a complex area where it is easy to make mistakes.

Second, the module will (normally) come pre-certified, removing another time consuming and costly step in the development process.

Lastly, the final procurement and assembly of the end product is simpler, with a pre-tested module replacing a large number of individual components.

In the particular case of the Insight SiP module, it is also unlikely that the customer will be able to design a solution as small, as achieving this level of miniaturisation has taken significant R+D.

In the end the choice depends on the particular circumstances of a project but certainly, unless the volumes for a product are going to be very high (several hundred thousand pieces per year), it is unlikely a discreet design will make sense when all factors are taken into account.

Typical Applications

For a number of years Insight SIP has been designing leading edge SIP based RF modules, for WiFi, GPS or cellular front ends, many of which are to be found in today's Smartphones. With its Bluetooth Smart modules, it is now able to offer this technology not just to high volume purchasers in the mobile phone market, but also to the general electronics design community. The Insight SiP Bluetooth Smart modules is designed into many applications such as temperature measurement (STEMP Smart Temperature Patch), gas measurement (Microtronics H2S sensor), industrial control (TeepTrak), wearable fitness monitor (Arion), Vernier Caliper (Sylvac), car park barrier control (ComThings) plus many more.

Characteristics

The new modules are some of the smallest on the market at only 8 x 8 mm in x/y dimensions, with a thickness less than 1mm.

The ISP15 and 18 Series modules has been designed to offer the very latest in BLE technology in the smallest possible package.

The 1507 module, for example integrates the nRF52832 chip from Nordic Semiconductor - offering a 32 bit ARM Cortex CPU, 512B flash memory, analog and digital peripherals SPI, I2C and GPIO. Nordic is the established leader in the Bluetooth chipset market. Combined with an integrated 32 MHz and 32khz crystal, DC/DC converter, RF antenna and matching circuit, this module forms a standalone Bluetooth Low Energy node, with market-leading performance.  The module is fully certified for global markets. Other modules in the 15/18 series offer the same core functionality with different feature/memory/price trade offs, making the Insight SIP offering one of the most flexible in the market.

Design Considerations - RF and Antenna Issues

When using the ISP range of Smart Bluetooth modules there are very few special requirements apart from being careful to ensure that the antenna area is devoid of metal. The drawing below indicates the ideal antenna keep-out zone:

Following the above rule will ensure there is a good RF transmission from the PCB. Of course, normally the application PCB will sit in some kind of housing, and one has to be careful that there is nothing in the complete solution that would adversely affect the radio connection. Whilst all engineers would be aware that you cannot put an RF solution in a metal box(!), RF interference effects can be subtle, and early testing of the complete solution is advised.

We are often asked what range can be achieved with our modules. However, most RF products specifications will quote a range under ideal conditions (typically 1m above ground with no obstructions), but in reality, most real-life situations are nowhere near as straightforward. For example, any solution that is used close to the human body (e.g. some kind of wearable or hand-held solution) will significantly reduce the real range. So whilst we can confidently state that our modules can achieve a range of over 50m in ideal circumstances, it is important to test an application under realistic conditions.

A further aspect of any antenna is the directional performance. If one cannot be sure of how the application device will be oriented, it is important that the antenna has an omnidirectional performance. This was a key design consideration of the Insight SiP modules which have a largely spherical radiation pattern. A more directional antenna would be fine if the orientation of the solution is fixed and know, but if not, one could find the solution stopped working under certain conditions (i.e. if the system was radiating mainly into the human body, for example).

Power Consumption

We are often asked about power consumption for BLE based solutions, as often a key design aim is for the application to run for a long period – months, or maybe even years – off a small coin cell battery.

Unfortunately, it is very hard to give a simple answer to such questions. Vendors often focus on key performance numbers such as peak Rx/Tx current, but the reality is the issue of power consumption is much more complex.

BLE achieves its low power performance by being in a deep sleep state most of the time. When it is a connection state, the transmit and receive cycle are quite short, although these require the highest current. There is also normally a processing cycle, where the radio transmission is off, but the processor active.

Thus the overall power consumption of a solution depends on several factors – the frequency of connection required, the speed the chip can wake up, the quantity of data transmitted (and this length of the transmission cycle), and the amount of processing required (and the speed of the processor. By looking at the above figures, one can see that peak Rx/Tx current are only one factor in assessing the performance of different BLE solutions, and not necessarily the most important factors.

Optimising the power consumption is largely a question of designing the application software appropriately, but it is useful to understand the underlying process to come up with the best design.

A further element related to power consumption is the inclusion of the 32KHz crystal in the solution (included in the 1507 module). This crystal is not essential for the solution to function correctly, but it does improve power consumption, by improving the timing of the wake up cycle, and thus maximising the “sleep” time.

Certification

Whilst certification is not strictly speaking a “design” activity, it is worth mentioning as it is a task that would typically expected of the engineering department

Requirements vary according to territory, but normally RF enabled solutions require certification by the relevant national or supra-national body. Typically this involves engaging third party accredited laboratory to carry out a series of tests to ensure that the RF application is “well-behaved” – i.e. it only radiated in the bands that it is meant to, and at the power levels expected. Of course, if any tests are failed, a re-design is required.

Each product has to individually certified (even if it shares some design with a similar product).

As stated previously, this is an area where a module can save time and money, as modules such as the ISP15 and 18 Series are pre-certified for global markets by the FCC (USA), CE (Europe) and Telec (Japan). In the case, the test process is either not required of vastly simplified, and all is required is a reference to the module certification number.

The ISP15 and ISP18 Series Modules

Our new ISP 15 and 18 Series modules are an example of how SIP can add significant value to the design process for chipsets requiring RF technology. Building on the success of its ISP13xx series modules, Insight SIP has launched the ISP15 and 18 Series devices using the latest generation of chip technology from market leader Nordic Semiconductor. This offers the most comprehensive and flexible range of BLE devices on the market, with a common package and basic pinout.

Getting Started and Support

To support product developers, Insight SIP offers a complete development kit together with sample software that provides everything required out of the box to start developing a solution on day one. A complete breadboard can be built using the kit together with external sensor development kits so that software development can proceed in parallel with hardware design.