FPGAs Power PC Digital TV
Using FPGAs in USB-powered DVB applications

by Michael Sarpa, Quicklogic Corporation

Digital Video Broadcast (DVB) continues to make worldwide inroads into the delivery of video to the home and on the road. While there are differences across the geographical markets, and the U.S. has been slow to adopt DVB, in Europe and many other areas of the world, DVB is becoming the standard through which consumers will receive their video content. DVB can be delivered to end users in a variety of ways including digital satellite, digital cable, and digital terrestrial transmissions. Thus, a new market has emerged for vendors providing delivery vehicles for DVB signals.

There are many advantages of DVB over traditional analog television signals, including picture quality and resolution, widescreen format, higher quality audio, and increased channel capability. More importantly, DVB allows the merging of various electronic media receivers, blurring the distinction between televisions, radios, PCs, PDAs, etc. One of the results of the advances in DVB technology is the ability to receive video signals on other media devices rather than just the traditional television monitors. With the increased demand for mobility and wireless connectivity, users want to be able to receive video signals while on the move, not just in their living rooms. Consumers expect to receive video, audio, Internet, e-mail, instant messenger, and other services on any electronic devices in the home, office or on the move. This creates a challenge for designers to be able to deliver the digital video content to PCs and handheld devices cheaply and efficiently. In addition, the receivers must be able to meet extremely low power requirements in order to give users reasonable battery life while viewing video content while “unplugged.”

One of the most popular new ways to receive DVB broadcast is on the home or office PC. For desktop PCs power is generally not a concern, since AC-power is typically readily available at the desktop station. However, in order to successfully support laptop video reception, the DVB receiver must be able to be powered directly from the PC and must not significantly reduce the battery life of the laptop. The ubiquitous USB connection provides a method to connect the DVB receivers quickly and easily to desktop and laptop PCs, and provides a power source. A quick review of the USB requirements helps define the power limitations. The USB specification defines a unit load as a 100 mA current draw. The maximum peak current that USB-attached devices are allowed to consume is five unit loads, or 500 mA. Thus, any successful DVB receiver using the USB interface must be able to remain below this limit in order to meet the specification.

So now we have the makings of a basic design for a DVB receiver to bring digital video to a PC environment. A basic design for a DVB receiver powered by a USB connection is shown in Figure 1. The electronic circuitry of the device can be divided into three basic functions, a DVB receiver, a USB controller, and a digital logic interface between the two. Each portion of the design is briefly described below.

Figure 1. USB-powered DVB Receiver design.

The first function is the DVB receiver device. A basic block diagram for a simple DVB receiver is shown in Figure 2. The main components include: a source decoder to differentiate between satellite, cable and terrestrial signals; a channel decoder to tune in the appropriate signal, control picture quality, and perform any required video processing; an audio decoder to control sound quality and perform sound processing; and an external interface to send the signals out to the receiving device, such as a PC.

Figure 2. DVB Receiver basic functions.

The second device is the USB controller. A basic block diagram for a simple USB controller is shown in Figure 3. The main components include: a microcontroller to manage the data transmission; a USB transceiver to send and receive the USB messages; on-chip memory (RAM, FIFO, etc.) to store and forward the information; and an external bus interface to communicate with other devices.

Figure 3. USB Controller basic functions.

Finally, since many of these two previous devices do not have compatible bus interfaces, a third device is required to allow the devices to communicate. In most cases, a standard off-the-shelf solution does not exist to connect the two devices together. The quickest and easiest method to connect the devices is to use an FPGA to provide the digital logic functionality required to have the devices interface to one another. However,

The USB specification mandates that the device must never exceed a peak current of 500 mA. Since the USB specification also requires a voltage of 5V for VBUS, the maximum peak power consumption cannot exceed 2.5 W. In this example, the chosen Digital Video receiver’s peak power consumption is 1.5W, while the USB Controller’s peak power consumption is 600 mW. This creates the design challenge: connecting the two critical components using a digital logic device that consumes less than 400 mW. Many FPGA devices consume considerably higher power than this limit. To meet this need, the designer chose the low power Eclipse II FPGA device from QuickLogic, the QL8025, which provided enough digital logic to successfully interface the two other devices; enough performance to meet the transmission speeds; and low enough power consumption to meet the USB specification.

QuickLogic’s Eclipse II family provides extremely low-power FPGAs with the density, features and performance to meet needs in the wireless and DVB marketplace. With five members in the family, a variety of package types including very small form factors, and standby currents as low as 22 uA, Eclipse II fits well in all handheld and battery-powered applications where logic density and performance in needed, but the design must also meet a tight power budget.

The ever-increasing demand for video content on-demand is driving a need for digital video transmission, and the desire to receive this content at non-traditional locations is driving the need for DVB receivers for laptop and desktop PCs. QuickLogic FPGA devices can help stitch the various components together while consuming very little power, so that these designs can be successfully developed within the PC limitations and so that designers can meet ever-stringent power requirements.

Michael Sarpa, Quicklogic Corporation

March 23, 2004

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