Rigol Employs Blackfin® for Virtual Digital Storage Oscilloscopes and Spectrum Analyzers

Oscilloscopes — those fundamental tools designers, programmers, and technicians use to test equipment as they design it, debug software that drives electronic circuits, or troubleshoot malfunctioning equipment — have come a long way since the original cathode-ray oscilloscopes (CRO). Those early oscilloscopes, which are now referred to as analog oscilloscopes, included a cathode-ray tube, a vertical amplifier, a timebase, a horizontal amplifier, and a power supply. Today's digital storage oscilloscopes (DSOs) are so-called because analog data is first digitized via analog-to-digital converters (ADCs), and then stored in memory, after which high-speed signal processors are used to further "process" the acquired signals. DSOs often run application-specific signal-analysis software to extract information particular to high-end applications, telecommunications being just one popular example.

Rigol Technologies, Inc. of Beijing, P.R. China, was founded in 1998 as a manufacturer of DSOs, signal generators, spectrum analyzers, and logic analyzers. Rigol also sells virtual instruments, which includes virtual DSOs, signal generators, spectrum analyzers, and logic analyzers. The company's products are widely used in test, measurement, and monitoring, as well as for research and development in universities and colleges. Rigol's products are also widely used for high-speed testing applications such as telecommunications physical layer testing, video testing, and high-speed digital design verification. When Rigol was looking for a signal processing platform versatile and powerful enough for its entire family of products, it turned to the Analog Devices, Inc. (ADI) Blackfin® ADSP-BF531 processor.

One reason Rigol chose ADI's Blackfin processor is because Blackfin inherently provides both microcontroller (MCU) and signal-processing functionality in a unified architecture, eliminating the need for separate digital signal and control processors. The processor's price/performance was another major attraction for Rigol as Blackfin offers unprecedented processing power for the cost.

The Whole Family
Rigol manufactures a complete line of DSOs in two families — the DS5000C and DS50000M and the DS3000B and DS3000M — which are available in color and monochromatic displays, and come with a variety of other features to meet the individual requirements of customers. The oscilloscopes vary in terms of bandwidth, timebase (which sets the speed at which the trace line is drawn and calibrates it in seconds per division), sample rate, and the number of channels (which allows more than one input signal to be displayed), amount of memory, trigger type (pulse from an external source, video, or edge trigger), and many other variables.

Rigol also manufactures a full line of virtual instruments. These include oscilloscopes with spectrum analyzers, which use the Fast Fourier transform (FFT), a mathematical process that transforms a waveform into the components of its frequency spectrum; oscilloscopes with both spectrum analyzers and logic analyzers; portable oscilloscopes that include spectrum analyzers and batteries; and the first DSOs to be integrated with signal generators, which produce an alternating current (AC) and are used to test or measure circuits.

The beauty of the Blackfin processor family is that it was specifically designed to meet the computational demands and power constraints of industrial/instrumentation and communications applications like Rigol's. Blackfin processors combine breakthrough signal-processing performance and power efficiency with a RISC programming model, allowing flexible resource allocation between hard real-time signal-processing tasks and system control tasks on the same processor. The programmable nature of the Blackfin processor made it easy for Rigol to adapt its Blackfin-based hardware platform to create a whole family of products at price points that meet a wide variety of customers' requirements.

Rigol also found that Blackfin's rich set of peripherals allowed the company to make a smaller, low cost product. Blackfin's ADSP-BF531 processor contains peripherals that are connected to the core via several high bandwidth busses, providing flexibility in system configuration as well as excellent overall system performance. General-purpose peripherals include functions such as UART, timers with pulse width modulation (PWM) and pulse measurement, general-purpose flag I/O pins, a real-time clock, and a watchdog timer. In addition, the processor contains high-speed serial and parallel ports for interfacing to a variety of audio, video, and modem codec functions, an interrupt controller for flexible management of interrupts from the on-chip peripherals or external sources, and power management control functions to tailor the performance and power characteristics of the processor and system to many application scenarios.

"Rigol just couldn't say enough about the superb service and technical support it received from ADI, which also went a long way to speeding time to market."

In particular, the parallel peripheral interface (PPI) port enabled Rigol to connect its LCD. The company used Blackfin's serial ports (SPORTs) to connect to the ADC. Rigol used the serial peripheral interface (SPI) to connect the keyboard, the UART port for communication, the external bus interface unit (EBIU) to connect to the Ethernet, and the general purpose I/O (GPIO) for the LEDs.

All of the peripherals, except for the general-purpose I/O, real-time clock, and timers, are supported by a flexible DMA structure. There is also a separate memory DMA channel dedicated to data transfers between the processors' various memory spaces, including external SDRAM and asynchronous memory. Multiple on-chip busses running at up to 133 MHz provide enough bandwidth to keep the processor core running with activity on all of the on-chip and external peripherals. In the past, Rigol used a C5000 processor from Texas Instruments.

Fast Time to Market
Several factors came together to help speed the time to market for Rigol's numerous DSO products. For one, Rigol says that the features of Blackfin made it easy for the company to set up the whole system and the simple fact that they did not have to use two chips, one for system control tasks and another for signal processing, was easier as well. Also, Rigol just couldn't say enough about the superb service and technical support it received from ADI, which also went a long way to speeding time to market.

For tools, Rigol took advantage of ADI's VisualDSP++, a project management environment that lets programmers develop and debug an application. It includes an easy to use assembler that is based on an algebraic syntax, an archiver (librarian/library builder), a linker, a compiler, and a C/C++ runtime library that includes DSP and mathematical functions. Rigol also used ADI's ADDS-HPPCI-ICE and ADDS-HPUSB-ICE emulators, which enabled the company to download code at speeds of up to 2.2 Mb/sec through the Blackfin's JTAG interface. The emulator allows developers to load code, set breakpoints, observe variables, observe memory, and examine registers.

The flexible breadth of Blackfin's capabilities has triggered sweeping changes in Rigol's product line, and the company plans to vertically expand its product offerings, giving its customers more choices at a wide range of price points, with the help of other Blackfin-family processors from ADI.

For more information on Rigol, please visit Rigol.

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