ADL5910

Data Sheet

Rev. 0 | Page 12 of 22

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 14 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

2

3

Ω

Ω

Q

RFIN

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 15 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 also affects the

response time, as shown in Figure 6.

CH2 1.0V

M10ns 20GS/s

A CH2

400mV

2

3

Ω

Ω

Q

RFIN

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

Figure 16 shows the response of the Q output, which goes low

when the input threshold is exceeded. As shown in Figure 16, the

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

CH2 1.0V

M10ns 20GS/s

A CH2

1.36V

2

3

Ω

Ω

Q

RFIN

Voltage Set to Trigger at −10 dBm (Overdrive Level = 3 dB)