MAX5894_07 Datasheet, PDF(20/33 Page) Maxim Integrated Products – 14-Bit, 500Msps, Interpolating and Modulating Dual DAC with CMOS Inputs

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MAX5894_07 Datasheet, PDF (20/33 Pages) Maxim Integrated Products – 14-Bit, 500Msps, Interpolating and Modulating Dual DAC with CMOS Inputs

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14-Bit, 500Msps, Interpolating and Modulating

Dual DAC with CMOS Inputs

The programmable interpolation filters multiply the

MAX5894 input data rate by a factor of 2x, 4x, or 8x to

separate the reconstructed waveform spectrum and the

DAC image. The original spectral images, appearing at

around multiples of the input data rate, are attenuated

by the internal digital filters. This feature provides three

benefits:

1) Image separation reduces complexity of analog

reconstruction filters.

INPUT

SPECTRUM

AND FIRST

FILTER

RESPONSE

SIGNAL

IMAGE

2fS

FILTER

RESPONSE

3fS

4fS

2) Lower input data rates eliminate board-level high-

speed data transmission.

3) Sin(x)/x rolloff is reduced over the effective bandwidth.

Figure 9 illustrates a practical example of the benefits

when using the MAX5894 in 2x, 4x, and 8x interpolation

modes with the third filter configured as a lowpass filter.

With no interpolation filter, the first image signal appears

in the second Nyquist zone between fS / 2 and fS. The first

interpolating filter removes this image. In fact, all of the

NO INTERPOLATION

5fS

6fS

7fS

8fS

OUTPUT

SPECTRUM

OF THE

FIRST

FILTER

SIGNAL

INPUT

SPECTRUM

AND

SECOND

FILTER

RESPONSE

SIGNAL

IMAGE

2fS

3fS

4fS

IMAGE

2fS

3fS

4fS

2x INTERPOLATION

5fS

6fS

7fS

8fS

FILTER

RESPONSE

5fS

6fS

7fS

8fS

OUTPUT

SPECTRUM

OF THE

SECOND

FILTER

SIGNAL

IMAGE

4x INTERPOLATION

2fS

3fS

4fS

5fS

6fS

7fS

8fS

INPUT

SPECTRUM

AND THIRD

FILTER

RESPONSE

SIGNAL

FILTER

RESPONSE

IMAGE

2fS

3fS

4fS

5fS

6fS

7fS

8fS

OUTPUT

SPECTRUM

OF THE

THIRD

FILTER

SIGNAL

2fS

3fS

4fS

IMAGE

8x INTERPOLATION

5fS

6fS

7fS

8fS

Figure 9. Spectral Representation of Interpolating Filter Responses (Output Frequencies are Relative to the Data Input Frequency, fS)

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