ADMV4530 datasheet(36/64 Pages) AD

36 / 64 page

Data Sheet

ADMV4530

THEORY OF OPERATION

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Rev. C | 36 of 64

I/Q MODE MIXER SETUP

In baseband quadrature modulation mode, the input impedance of

the baseband pins (IN, IP, QN, and QP) are 100 Ω differential.

These inputs can be driven with a dc-coupled 100 Ω differential

source. IN and IP are the differential baseband I inputs, and QN

and QP are the differential baseband Q inputs. These inputs can

operate from a common-mode voltage range of 0 V to 2.5 V. When

operating in I/Q mode, program the following registers:

►

When VCM changes, program Register 0x103 by using the following

formulas for each mode.

In I/Q mode, for VCM = 0.0 V to 1.5 V, set MIXER_VCM =

ROUND(23.8 × VCM + 80.7).

In I/Q mode, for VCM = 1.5 V to 2.5 V, set MIXER_VCM =

ROUND(23.8 × VCM + 1.3).

The I/Q mode default for VCM = 0.5 V is MIXER_VCM = 93 = 0x5D.

I/Q MODE LO NULLING

To perform LO nulling in I/Q mode, apply a differential dc offset

on the I and Q inputs. Note that LO nulling is a two-step process.

When LO nulling is done on the I side, keep the Q side at VCM,

and when LO nulling is done on the Q side, the I side must be kept

at VCM or at the determined value in the first step. The optimal LO

null is when settings from the I side and the Q side are combined.

It is important to keep VCM constant. Therefore, when a dc offset

is applied on the negative input (VCMN), the same offset must be

applied on the positive input (VCMP) in the opposite direction (VCMP

± dc offset and VCMN

∓ dc offset) to allow the average VCM to

hold constant to coincide with the value programmed in Register

0x103. LO nulling at a single point is optimal at that particular

frequency and temperature, and the absolute level (dBm) of the LO

to RF feedthrough remains the same across gain settings using the

VCTR_RF input.

For example, it is possible to null LO down to −50 dBm with

VCTR_RF = 1.8 V, depending on the resolution of the dc offset

applied and the temperature (as shown in Figure 28 and Figure 29),

where LO nulling = 29 GHz. When LO nulling = 29 GHz, the LO to

RF feedthrough is <−20 dBm over temperature, and the frequency

range is from 28 GHz to 30 GHz.

I/Q MODE SIDEBAND REJECTION NULLING

In I/Q 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 −45 dBc for a particular frequency. The sideband rejection de-

grades to −35 dBc if the frequency or temperature changes (shown

in Figure 27 and Figure 30).

IF GAIN CONTROL

As shown in the functional block diagram (see Figure 1), the

ADMV4530 incorporates an IF amplifier with analog gain control.

The analog voltage for this IF amplifier can either be provided by

the internal AGC loop or by applying an external VCTR_IF voltage

to the EXT_CAP_N (Pin 10). The voltage range for the IF amplifier

gain control is 0 V to 3.3 V, with a negatively sloping linear region

between 0.9 V and 2.2 V, as shown in Figure 38. The typical slope

within linear region is −32 dB/V.

IF MODE MIXER SETUP

The ADMV4530 features the ability to upconvert a real IF input

anywhere from 2 GHz to 3 GHz. When operating in IF mode

program the following registers:

►

When VCM changes, program Register 0x103 by using the following

formula:

MIXER_VCM = ROUND(0.3 × (128 − TARGET_MIX-

ER_DC_OFFSET) + 80.7)

(21)

where TARGET_MIXER_DC_OFFSET is the value programmed

into Register 0x106 to Register 0x109.

ADMV4530 Datasheet(PDF) 36 Page - Analog Devices

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