ADL5904ACPZN-R7 datasheet(22/28 Pages) AD

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Data Sheet

ADL5904

Rev. 0 | Page 21 of 27

BASIC CONNECTIONS FOR THRESHOLD DETECTION

VPOS

3.3V

THRESHOLD

VOLTAGE

INPUT

RESET

INPUT

CALIBRATION

VOLTAGE OUTPUT

4.0

2Ω

100nF

100pF

0.1µF

ENABLE/

DISABLE

ENVELOPE

DETECTOR

RMS

–

ADL5904

VPOS

GND

VRMS

RST

RFIN

470nF

VIN–

DECL

82.5Ω

ENBL

CRMS

VCAL

DNC

RFIN

Figure 49. Basic Connections for Threshold Detection

Figure 49 shows the basic connections for operating the ADL5904

in threshold detection mode. A threshold voltage is applied to the

VIN− input that corresponds to the RF power level at which the

circuit trips. When the level on RFIN drives the envelope detector

to an output voltage that exceeds the programmed threshold, the

comparator output goes high causing the Q output to latch high

and the Q output to latch low. The levels on Q and Q can be

reset by setting the RST pin high (note that the RST function is

level triggered, not edge triggered). Q and Q are held at low and

high states respectively as long as RST is high, even if the RF input

level is exceeding the programmed threshold voltage. RST must

be taken low for the threshold detection circuit to reactivate.

Q AND Q RESPONSE TIME

Figure 50 shows the response of the Q output when the input

power exceeds the programmed threshold by approximately

1 dB. The response time from the input power exceeding the

threshold to the Q output reaching 50% of its final value is

approximately 12 ns

CH2 1.0V

M10ns 20GS/s

A CH2

1.52V

Ω

CH3 100mV

Ω

Figure 50. Q Output Response at 900 MHz, PIN = Off to −9 dBm, Overdrive

Threshold Voltage Set to Trigger at −10 dBm (Overdrive Level = 1 dB)

The response time of the Q and Q outputs is somewhat dependent

on the level of overdrive with higher overdrive levels, giving a

slightly faster response time. Figure 51 shows the response of

the Q output when the RF input level overdrives the threshold

by 5 dB, which reduces the response time to approximately 12 ns.

Overdrive levels beyond 5 dB tend not to reduce the response

time below this level. Capacitive loading on Q and Q also affects

the response time, as shown in Figure 35.

CH2 1.0V

M10ns 20GS/s

A CH2

400mV

Ω

CH3 200mV

Ω

Figure 51. Q Output Response, PIN = Off to −5 dBm, Overdrive Threshold

Voltage Set to Trigger at −10 dBm (Overdrive Level = 5 dB, VIN− = 75 mV)

Figure 52 shows the response of the Q output, which goes low

when the input threshold is exceeded. As shown in Figure 52, the

response time of Q is equal to that of the Q output.

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