AD9670EBZ datasheet(35/53 Pages) AD

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AD9670

Data Sheet

Rev. A | Page 34 of 52

I/Q Demodulator and Phase Shifter

The I/Q demodulators consist of double-balanced, harmonic

rejection, passive mixers. The RF input signals are converted

into currents by transconductance stages that have a maximum

differential input signal capability matching the LNA output full

scale. These currents are then presented to the mixers, which

convert them to baseband (RF − LO) and 2× RF (RF + LO).

The signals are phase shifted according to the codes programmed

into the SPI latch (see Table 27). The phase shift function is an

integral part of the overall circuit. The phase shift listed in Table 20

is defined as being between the baseband I or Q channel outputs.

As an example, for a common signal applied to a pair of RF inputs

to an AD9670, the baseband outputs are in phase for matching

phase codes. However, if the phase code for Channel 1 is 0000

and that of Channel 2 is 0001, Channel 2 leads Channel 1 by

22.5°.

Table 20. Phase Select Code for Channel-to-Channel Phase Shift

Φ Shift

I/Q Demodulator Phase

(SPI Register 0x02D, Bits[3:0])

0°

0000

22.5°

0001 (not valid in 4LO mode)

45°

0010

67.5°

0011 (not valid in 4LO mode)

90°

0100

112.5°

0101 (not valid in 4LO mode)

135°

0110

157.5°

0111 (not valid in 4LO mode)

180°

1000

202.5°

1001 (not valid in 4LO mode)

225°

1010

247.5°

1011 (not valid in 4LO mode)

270°

1100

292.5°

1101 (not valid in 4LO mode)

315°

1110

337.5°

1111 (not valid in 4LO mode)

AD9670EBZ Datasheet(PDF) 35 Page - Analog Devices

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