Data Sheet

ADRF5021

Rev. A | Page 9 of 12

THEORY OF OPERATION

The ADRF5021 requires a positive supply voltage applied to the

VDD pin and a negative supply voltage applied to the VSS pin.

Bypassing capacitors are recommended on the supply lines to

minimize RF coupling.

The ADRF5021 is internally matched to 50 Ω at the RF common

port (RFC) and the RF throw ports (RF1 and RF2); therefore,

no external matching components are required. All of the RF

ports are dc-coupled to 0 V, and no dc blocking is required at the

RF ports when the RF line potential is equal to 0 V. The design

is bidirectional; the RF input signal can be applied to the RFC

port while the RF throw port (RF1 or RF2) is output or vice versa.

The ADRF5021 incorporates a driver to perform logic functions

internally and to provide the user with the advantage of a simplified

control interface. The driver features two digital control input

pins, CTRL and EN.

When the EN pin is logic low, the RF1 to RFC path is in an

insertion loss state, and the RF2 to RFC path is in an isolation

state, or vice versa, depending on the logic level applied to the

CTRL pin. The insertion loss path (for example, RF1 to RFC)

conducts the RF signal equally well in both directions between

its throw port (for example, RF1) and common port (RFC). The

isolation path (for example, RF2 to RFC) provides high loss

between the insertion loss path and its throw port (for example,

RF2) terminated to an internal 50 Ω resistor.

When the EN pin is logic high, both the RF1 to RFC path and

the RF2 to RFC path are in an isolation state regardless of the

logic state of CTRL. RF1 and RF2 ports are terminated to

internal 50 Ω resistors, and RFC becomes open reflective.

The ideal power-up sequence is as follows:

1. Power up GND.

2. Power up VDD and VSS. The relative order is not

important.

3. Power up the digital control inputs. The relative order of

the logic control inputs is not important. However,

powering the digital control inputs before the VDD supply

can inadvertently forward bias and damage the internal

ESD protection structures.

4. Apply an RF input signal.

Table 4. Control Voltage Truth Table

Digital Control Input

RF Paths

EN

CTRL

RF1 to RFC

RF2 to RFC

Low

Low

Isolation (off)

Insertion loss (on)

Low

High

Insertion loss (on)

Isolation (off)

High

Low

Isolation (off)

Isolation (off)

High

High

Isolation (off)

Isolation (off)