ADRF6702 datasheet(18/36 Pages) AD

18 / 36 page

ADRF6702

Rev. 0 | Page 18 of 36

IQ FILTERING

DEVICE PROGRAMMING AND REGISTER

SEQUENCING

An antialiasing filter must be placed between the DAC and

modulator to filter out Nyquist images and broadband DAC

noise. The interface for setting up the biasing and ac swing

discussed in the Adding a Swing-Limiting Resistor section,

lends itself well to the introduction of such a filter. The filter

can be inserted between the dc bias setting resistors and the

ac swing-limiting resistor. Doing so establishes the input and

output impedances for the filter.

The device is programmed via a 3-pin SPI port. The timing

requirements for the SPI port are shown in Table 3 and Figure 2.

Eight programmable registers, each with 24 bits, control the

operation of the device. The register functions are listed in

Table 9. The eight registers should initially be programmed

in reverse order, starting with Register 7 and finishing with

programmed, any of the registers can be updated without any

attention to sequencing.

Unless a swing-limiting resistor of 100 Ω is chosen, the filter

must be designed to support different source and load

impedances. In addition, the differential input capacitance of

the I and Q inputs (1 pF) should be factored into the filter

design. Modern filter design tools allow for the simulation and

design of filters with differing source and load impedances as

well as inclusion of reactive load components.

Software is available on the ADRF6702 product page at

www.analog.com that allows programming of the evaluation

board from a PC running Windows® XP or Windows Vista.

To operate correctly under Windows XP, Version 3.5 of

Microsoft .NET must be installed. To run the software on

a Windows 7 PC, XP emulation mode must be used (using

Virtual PC).

BASEBAND BANDWIDTH

Figure 38 shows the frequency response of the ADRF6702’s

baseband inputs. This plot shows 0.5 dB and 3 dB bandwidths

of 350 MHz and 750 MHz respectively. Any flatness variations

across frequency at the ADRF6702 RF output have been

calibrated out of this measurement.

–10

–8

–6

–4

–2

100

1000

BB FREQUENCY (MHz)

Figure 38. Baseband Bandwidth

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