LF-to-2.5GHz Dual Logarithmic Detector/

Controller for Power, Gain, and VSWR Measurements

16

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Comparators/Window Detectors

The MAX2016 integrates two comparators for use in

monitoring the difference in power levels (gain) of

RFINA and RFINB. The thresholds of the two compara-

tors are set to the voltage applied to the CSETL and

CSETH pins. The output of each comparator can be

monitored independently or from the COR output that

ORs the outputs of the individual comparators. This can

be used for a window-detector function.

These comparators can be used to trigger hardware

interrupts, allowing rapid detection of over-range condi-

tions. These comparators are high-speed devices.

Connect high-value bypass capacitors (0.1µF) between

each comparator threshold input (CSETL and CSETH)

to ground to provide a solid threshold voltage at high

switching speeds.

Some applications may benefit from the use of hystere-

sis in the comparator response. This can be useful for

prevention of false triggering in the presence of small

noise perturbations in the signal levels, or with signals

with large amplitude modulation. To introduce hysteresis

into the comparator output, connect a feedback resistor

from COUTL to CSTEL. Select the value of this resistor,

in combination with the resistive-divider values used to

set threshold-level CSETL, to set the amount of hystere-

sis. Set the parallel combination of resistors connected

to CSETL to be less than 10k

Ω for best performance.

Figure 8 illustrates the use of these comparators in a

gain-monitoring application. The low comparator has its

threshold (CSETL) set at a low-gain trip point. If the

gain drops below this trip point, the COUTL output

goes from a logic 0 to a logic 1. The high comparator

has its threshold (CSETH) set at a high trip point. If the

gain exceeds this trip point, the COUTH output goes

from logic 0 to logic 1. The window comparator output

(COR) rests a logic 0 if the gain is in the acceptable

range, between CSETL and CSETH. It goes to a logic 1

if the gain is either above or below these limits.

Power-Supply Connection

The MAX2016 is designed to operate from a single

+2.7V to +3.6V supply. To operate under a higher sup-

ply voltage range, a resistor must be connected in series

delivered to the chip. For a +4.75V to +5.25V supply,

use a 37.4

Ω (±1%) resistor in series with the supply.

Layout Considerations

A properly designed PCB is an essential part of any

RF/microwave circuit. Keep RF signal lines as short as

possible to reduce losses, radiation, and inductance.

For the best performance, route the ground pin traces

directly to the exposed pad under the package. The

PCB exposed pad MUST be connected to the ground

plane of the PCB. It is suggested that multiple vias be

used to connect this pad to the lower level ground

MAX2016

RFINA

RFINB

IN

LOGARITHMIC

DETECTOR

LOGARITHMIC

DETECTOR

OUTD

SETD

COUPLER

COUPLER

RF BLOCK

OUT

CSETL

COR

CSETH

20k

Ω

Figure 8. Window Comparators Monitoring Mode. COR goes high if OUTD drops below CSETL or rises above CSETH.