ADL5390 datasheet(11/23 Pages) AD

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Data Sheet

ADL5390

Rev. A | Page 11 of 23

GENERAL STRUCTURE

THEORY OF OPERATION

The simplified block diagram given in Figure 26 shows a

matched pair of variable gain channels whose outputs are

summed and presented to the final output. The RF/IF signals

propagate from the left to the right, while the baseband gain

controls are placed above and below. The proprietary linear-

responding variable attenuators offer excellent linearity, low

noise, and greater immunity from mismatches than other

commonly used methods.

Since the two independent RF/IF inputs can be combined in

arbitrary proportions, the overall function can be termed

“vector multiplication” as expressed by

VOUT = VIRF × (VIBB/VO) + VQRF × (VQBB/VO)

where:

VIRF and VQRF are the RF/IF input vectors.

VIBB and VQBB are the baseband input scalars.

VO is the built-in normalization factor, which is designed to be

0.285 V (1/3.5 V).

The overall voltage gain, in linear terms, of the I and Q channels is

proportional to its control voltage and scaled by the normalization

factor, i.e., a full-scale gain of 1.75 (5 dB) for VI (Q)BB of 500 mV.

A full-scale voltage gain of 1.75 defines a gain setpoint of 1.0.

Due to its versatile functional form and wide signal dynamic

range, the ADL5390 can form the core of a variety of useful

functions such as quadrature modulators, gain and phase

adjusters, and multiplexers. At maximum gain on one channel,

the output 1 dB compression point and noise floor referenced to

50 Ω are 11 dBm and −148 dBm/Hz, respectively. The broad

frequency response of the RF/IF and gain control ports allows

the ADL5390 to be used in a variety of applications at different

frequencies. The bandwidth for the RF/IF signal path extends

from approximately 20 MHz to beyond 2.4 GHz, while the gain

controls signals allow for modulation rates greater than 200 MHz.

Matching between the two gain channels is ensured by careful

layout and design. Since they are monolithic and arranged

symmetrically on the die, thermal and process gradients are

minimized. Typical gain and phase mismatch at maximum gain

are <0.5 dB and <0.5°.

LINEAR

ATTENUATOR

LINEAR

ATTENUATOR

I-V

VQBB

Q CHANNEL

BASEBAND INPUT

VIRF,

I CHANNEL

SINGLE-ENDED

OR DIFFERENTIAL

VIBB

OUTPUT

DISABLE

SINGLE-ENDED

OR DIFFERENTIAL

Ω OUTPUT

VQRF,

Q CHANNEL

SINGLE-ENDED

OR DIFFERENTIAL

I CHANNEL

BASEBAND INPUT

V-I

Figure 26. Simplified Architecture of the ADL5390

NOISE AND DISTORTION

The signal path for a particular channel of the ADL5390

consists basically of a preamplifier followed by a variable

attenuator and then an output driver. Each subblock contributes

some level of noise and distortion to the desired signal. As the

channel gain is varied, these relative contributions change. The

overall effect is a dependence of output noise floor and output

distortion levels on the gain setpoint.

For the ADL5390, the distortion is always determined by the

preamplifier. At the highest gain setpoint, the signal capacity, as

described by the 1 dB compression point (P1dB) and the third-

order intercept (OIP3), are at the highest levels. As the gain is

reduced, the P1dB and OIP3 are reduced in exact proportion.

At the higher gain setpoints, the output noise is dominated by

the preamplifier as well. At lower gains, the contribution from

the preamplifier is correspondingly reduced and eventually a

noise floor, set by the output driver, is reached. As Figure 27

illustrates, the overall dynamic range defined as a ratio of OIP3

to output noise floor remains constant for the higher gain

setpoints. At some gain level, the noise floor levels off and the

dynamic range degrades commensurate with the gain reduction.

175

170

165

160

155

150

145

140

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

GAIN SETPOINT

DYNAMIC RANGE = OIP3 – (OUTPUT NOISE

FLOOR (NO CARRIER))

Figure 27. Dynamic Range Variation with Gain Setpoint

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