Altera Stratix II EP2S180 DSP Development Board Manuel d'utilisateur télécharger pdf (Page 27)

Altera Corporation Core Version a.b.c variable 2–19

Stratix II EP2S180 DSP Development Board Reference Manual

Board Components & Interfaces

D/A Converters

The Stratix II EP2S180 DSP development board has two D/A converters.

The D/A subsystem of the board has the following features:

■ The converters produce 14-bit samples at a maximum rate of 165

MSPS.

■ The analog output from each D/A converter is single-ended.

1 The D/A converters expect data in an unsigned integer format.

The D/A clock signals are output directly from the Stratix II device to the

converters.

Figure 2–5 shows the on-board circuitry after a D/A converter. The

output of a D/A converter chip, DAC904, consists of a current source

whose maximum value is 20 mA. This differential output is converted to

a single -ended output using an RF transformer. The DSP board uses a 1:1

ratio transformer to interface to a 50 ohm impedance load. Each of the

outputs is terminated with a 49.9 ohm resistor to ground. This circuit

results in outputs being AC-coupled and inherently isolated due to

transformer’s magnetic coupling. The output of the transformer is then

brought to an SMA connector.

Figure 2–5. On-Board Circuitry after D/A Converter

1 The development kit includes an SLP-50 anti-aliasing filter from

Mini-Circuits. This filter provides a 55-MHz cut-off frequency.

For systems with other bandwidth requirements, a variety of

anti-aliasing filters are available from commercial

manufacturers that suit system requirements.

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 57 58

Pas de commentaire

Altera Stratix II EP2S180 DSP Development Board Manuel d'utilisateur Page 27