ADMV4530 datasheet(37/64 Pages) AD

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Data Sheet

ADMV4530

THEORY OF OPERATION

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Rev. C | 37 of 64

IF MODE LO NULLING

LO nulling is performed in IF mode in a similar fashion as in I/Q

mode. However, dc offset is applied through Register 0x106 to

dc offset on the I side, and use Register 0x108 and Register 0x109

to force a dc offset on the Q side. It is important to sweep the

I and Q registers simultaneously in opposite direction so that the

following are true:

(MIXER_DC_OFFSET_IP + MIXER_DC_OFFSET_IN)/2 =

TARGET_MIXER_DC_OFFSET

(22)

(MIXER_DC_OFFSET_QP + MIXER_DC_OFFSET_QN)/2 =

TARGET_MIXER_DC_OFFSET

(23)

As in I/Q mode, LO nulling is two-step process. When LO nulling

on the I side, keep the Q side at the TARGET_MIXER_DC_OFF-

SET. When LO nulling on the Q side, keep the I side at the

TARGET_MIXER_DC_OFFSET, or at the determined value from

the first step. The optimal null is achieved when both settings

are combined. The recommended TARGET_MIXER_DC_OFFSET

value is 95 decimal (0x5F). It is recommended to keep the TAR-

GET_MIXER_DC_OFFSET above 63. The MIXER_DC_OFFSET

range for Register 0x106 to Register 0x109 is from 63 decimal to

127 decimal. The LO to RF feedthrough improves to approximately

−30 dB following this procedure. When the LO is nulled at a single

frequency and temperature, the LO to RF feedthrough is less than

−40 dBc, and the LO to RF feedthrough is less than −25 dBc across

frequency and temperature, as shown in Figure 57.

IF MODE SIDEBAND REJECTION NULLING

In IF mode, use Register 0x104 or Register 0x105 to perform

sideband rejection nulling. Each register has 128 settings, Bits[6:0].

Single frequency nulling allows sideband rejection to null down to

−50 dBc for a particular frequency. If the operating frequency or

temperature changes, sideband rejection nulling degrades. When

sideband rejection is nulled at 29 GHz, it is less than −30 dBc over

temperature and the frequency range is from 28 GHz to 30 GHz (as

shown in Figure 56).

ADMV4530 Datasheet(PDF) 37 Page - Analog Devices