ADL5910

Data Sheet

Rev. 0 | Page 16 of 22

APPLICATIONS INFORMATION

A COMPLETE INPUT PROTECTION CIRCUIT

Figure 18 shows a block diagram of a complete input protection

circuit that protects the input to a power amplifier or the input

to a receiver to frequencies of approximately 2.6 GHz. This circuit

consists of a single-pole, single throw (SPST) switch (for this

example, the HMC550A), an asymmetrical power splitter/coupler

circuit, and the ADL5910. The main signal path is through the

coupler and SPST switch. The circuit in this example protects

against input levels to the receiver or the power amplifier that

exceed 20 dBm.

Under normal operation, the switch is closed. The closed switch

results in insertion loss, which is the sum of the switch insertion

loss and the insertion loss of the splitter/coupler. In the example

shown in Figure 18, the coupling factor is 20 dB, which results

in an insertion loss of 1.72 dB. Different resistor values can

reduce the insertion loss, which results in a lower level on the

coupled signal. The insertion loss of the switch is approximately

0.7 dB, resulting in a total insertion loss of approximately 2.5 dB.

The coupled signal is applied to the RF input of the ADL5910.

Because of the coupling factor of 20 dB, the ADL5910 must be

configured to respond to input levels in excess of 2.5 dBm. As is

shown in Table 5 and Figure 18, the threshold level on VIN− must

be set to approximately 300 mV. If high triggering precision is

required, perform calibration because the threshold voltage for

a particular input power level varies from device to device.

When the output of the ADL5910 triggers after an overdrive

event, the Q output goes low and opens the HMC550A switch.

When the HMC550A switch is open, the attenuation in the

signal path increases to the specified isolation of the HMC550A

switch and the insertion loss of the coupler, ranging from 15 dB

to 40 dB based on frequency.

In the example shown in Figure 18, the Q output also drives an

interrupt input of a microprocessor or microcontroller.

Program the microprocessor or microcontroller to issue short

periodic reset pulses. After each reset pulse, the ADL5910 either

remains reset (if the input level drops below the threshold) or

reopens the switch.

2.5dB INSERTION LOSS

20dB

HMC550A

RFIN

(20dBm MAXIMUM)

300mV

R

ENVELOPE

DETECTOR

S

Q

Q

VIN–

ADL5910

RST

VCAL

RFIN

0.47µF

Q

RECEIVER OR

POWER APLIFIER

RFIN

(22.5dBm MAXIMUM)

RFIN

(2.5dBm

MAXIMUM)

4.99Ω

RESET

INT

4.99Ω

220Ω

62Ω

82.5Ω

MICROPROCESSOR

15

16

3

1

12

Q

13

Figure 18. A Complete Input Protection Circuit (Power Supply and Decoupling Omitted for Clarity)