Board Components
D/A Converters
The Stratix II EP2S60 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 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 output is connected to ground on the
board using a 51-Ωresistor, creating a Thevenin equivalent voltage source
of 1 V in series with a 51-Ωresistor. When loaded with an external 50-Ω
termination, the output swing is reduced to 0.5 VPP. Additionally, there is
a 27-pF capacitor in parallel with the output resistor resulting in a single-
pole, low-pass filter with an upper 3-dB frequency of approximately 230
MHz when externally loaded. The output is then brought to an SMA
connector.
Figure 5. On-Board Circuitry after D/A Converter
D/A Converter
Output
27 pf
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 to suit the system requirements.
Altera Corporation
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Preliminary
ALTERA [ ALTERA CORPORATION ]
