ADL5365

Rev. 0 | Page 17 of 24

CIRCUIT DESCRIPTION

The ADL5365 consists of two primary components: the radio

frequency (RF) subsystem and the local oscillator (LO) subsystem.

The combination of design, process, and packaging technology

allows the functions of these subsystems to be integrated

into a single die, using mature packaging and interconnection

technologies to provide a high performance, low cost design

with excellent electrical, mechanical, and thermal properties.

In addition, the need for external components is minimized,

optimizing cost and size.

The resulting balanced RF signal is applied to a passive mixer

that commutates the RF input with the output of the LO subsystem.

The passive mixer is essentially a balanced, low loss switch that

adds minimum noise to the frequency translation. The only

noise contribution from the mixer is due to the resistive loss

of the switches, which is in the order of a few ohms.

As the mixer is inherently broadband and bidirectional, it

is necessary to properly terminate all the idler (M × N product)

frequencies generated by the mixing process. Terminating the

mixer avoids the generation of unwanted intermodulation

products and reduces the level of unwanted signals at the IF

output. This termination is accomplished by the addition of a

sum network between the IF output and the mixer.

The RF subsystem consists of an integrated, low loss RF balun,

passive MOSFET mixer, and a sum termination network.

The LO subsystem consists of an SPDT-terminated FET switch

and a three-stage limiting LO amplifier. The purpose of the LO

subsystem is to provide a large, fixed amplitude, balanced signal

to drive the mixer independent of the level of the LO input.

The IP3 performance can be optimized by adjusting the supply

current with an external resistor. Figure 37 and Figure 39

illustrate how various bias resistors affect the performance with a

5 V supply. Additionally, dc current can be saved by increasing

the resistor. It is permissible to reduce the dc supply voltage to

as low as 3.3 V, further reducing the dissipated power of the

part. (Note that no performance enhancement is obtained by

reducing the value of these resistors and excessive dc power

dissipation may result.)

A block diagram of the device is shown in Figure 49.

2

3

1

20

19

18

17

16

6

7

8

9

10

4

5

14

13

15

12

BIAS

GENERATOR

VPMX

RFIN

RFCT

COMM

COMM

LOI2

VPSW

VGS1

VGS0

LOI1

VCMI

IFOP

IFON

PWDN

COMM

VLO3

LGM3

VLO2

LOSW

NC

ADL5365

NC = NO CONNECT

11

LO SUBSYSTEM

The LO amplifier is designed to provide a large signal level to

the mixer to obtain optimum intermodulation performance.

The resulting amplifier provides extremely high performance

centered on an operating frequency of 1700 MHz. The best

operation is achieved with either high-side LO injection for RF

signals in the 1200 MHz to 1700 MHz range or low-side injection

for RF signals in the 1700 MHz to 2500 MHz range. Operation

outside these ranges is permissible, and conversion gain is

extremely wideband, easily spanning 1200 MHz to 2500 MHz,

but intermodulation is optimal over the aforementioned ranges.

The ADL5365 has two LO inputs permitting multiple synthesizers

to be rapidly switched with extremely short switching times

(<40 ns) for frequency agile applications. The two inputs are

applied to a high isolation SPDT switch that provides a constant

input impedance, regardless of whether the port is selected, to

avoid pulling the LO sources. This multiple section switch also

ensures high isolation to the off input, minimizing any leakage

from the unwanted LO input that may result in undesired IF

responses.

Figure 49. Simplified Schematic

RF SUBSYSTEM

The single-ended, 50 Ω RF input is internally transformed to a

balanced signal using a low loss (<1 dB) unbalanced-to-balanced

(balun) transformer. This transformer is made possible by an

extremely low loss metal stack, which provides both excellent

balance and dc isolation for the RF port. Although the port can

be dc connected, it is recommended that a blocking capacitor be

used to avoid running excessive dc current through the part.

The RF balun can easily support an RF input frequency range

of 1200 MHz to 2500 MHz.

The single-ended LO input is converted to a fixed amplitude

differential signal using a multistage, limiting LO amplifier.

This results in consistent performance over a range of LO input

power. Optimum performance is achieved from −6 dBm to

+10 dBm, but the circuit continues to function at considerably

lower levels of LO input power.