An embedded modem offers quick network access for applications with limited data transmission requirements. Today, more and more applications such as set-top boxes, electronic point-of-sale terminals (EPOS), digital video recorders, digital televisions and remote monitoring systems distribute information by taking advantage of widely available modem connectivity. The list of applications continues to grow.
In today's changing technology environment, there are several factors to take into consideration when choosing an embedded modem including integration, global compliance and the speed/feature requirements of the end application. Properly implemented integration is a compelling factor for design engineers because fewer external components significantly reduce the bill of materials (BOM) enabling an easier-to-use, lower cost solution. Knowledge of the end product function is an important factor in deciding the modem speed and country settings. A single design for all speeds and all countries offers greater flexibility and faster time-to-market by simplifying the design, manufacture and distribution process. Additionally, different applications such as EPOS terminals and set-top boxes, require different speeds ranging from 2400 bps to 56 Kbps. Flexibility offered by an embedded modem is also an important factor to consider. An application that needs an embedded modem that operates at 2400 bps today may need higher rates in the future. Leveraging an embedded modem family that can scale from 2400 bps to 56 Kbps using the same footprint eliminates the need to re-design the modem when an upgrade is required.
Diverse applications require specific features
The first step in selecting an embedded modem is to make sure the features match the needs of the application. In applications such as EPOS terminals and credit card readers, an embedded modem that operates at a lower speed can be used because it does not require a significant amount of data transmission at one time. On the other hand, personal video recorders (PVR) such as TiVo download an electronic programming guide and other large data files, which creates the need for a modem that operates at higher speeds.
To take the PVR example further, an embedded modem should offer caller ID decoding in order for incoming caller information to be displayed on the TV screen. Modems should also unobtrusively determine if the phone line is available or in use so that telephone calls will not be interrupted when the PVR attempts to download information. Additionally, during a data connection, the embedded modem should alert the host if a phone is picked up on the shared line.
High integration simplifies design, lowers cost
Once features required for the application are determined, examine the integration options. By integrating several components that make up an effective embedded modem into a compact chipset, it significantly reduces the BOM. Modems have four basic components: a controller, a DSP data pump, memory and a direct access arrangement (DAA). Some solutions integrate a modem controller and a DSP data pump but use external memory and a discrete DAA requiring numerous components.
A better alternative implements a silicon DAA which eliminates the need for a codec, an isolation transformer, relay, opto-isolator and a 2-to-4-wire hybrid. The Silicon Laboratories' ISOmodem embedded modem products are a good example. These products provide a standard UART interface, AT command support and integrated ROM and RAM, allowing the embedded modem to greatly simplify hardware and software development by easing design layout, procurement and compliance testing. Maximising integration increases the functionality on a given PCB, reduces the footprint and ultimately lowers the BOM.
Global design
Another important factor in designing in an embedded modem is global compliance. Different countries specify different standards and speeds for various applications. By sharing the same globally compliant line-side device, a single embedded modem design can be used in all countries and for all modem speeds ranging from 2400 bps to 56 Kbps. A single, globally compliant design reduces the time-to-market risks associated with PTT country approvals and design risks associated with emissions, immunity, safety and surge performance.
Modem connectivity needs to be cost effective, reliable and easy to implement. A fully featured, highly integrated solution can dramatically reduce design time and create a flexible solution that will evolve with the application.
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