ADL6012

Data Sheet

Rev. 0 | Page 20 of 24

ENVELOPE OUTPUT INTERFACE

The differential envelope outputs, VENV+ and VENV−, provide

the envelope information of the input signal. The ADL6012 is

designed to drive 100 Ω differential or a 50 Ω load on each

VENV± output when ac-coupled. It is important that the

VENV± outputs are not dc-coupled to 50 Ω load referenced to

ground, which results in excessive dc current flow to the load

that may exceed the output drive capability, depending on the

output common-mode voltage level. The ADL6012 is suitable

for AM and pulse modulation detection. See Figure 48 and

Figure 49 for the typical AM and pulse output response,

respectively. The device features an extremely fast response

time of approximately 1 ns or less.

For applications that require fast response to RF input levels or

pulsed RF detection, connect the envelope outputs to trans-

mission lines with a differential characteristic impedance of 100 Ω,

terminated with a 100 Ω differential load, so that the outputs are

impedance matched with no reflections from the load. Figure 61

shows the simplified ADL6012 output stage interfaced to a

100 Ω load with impedance controlled transmission lines.

The output impedance of the ADL6012 drives a differential 100 Ω

load. The differential VENV± output dc voltage is divided down

by the ratio of the load and output impedance. For example,

with a differential 100 Ω output load, the differential output

voltage is halved from the open load voltage. See Figure 62 for the

differential envelope output voltage vs. the input power with

various output loads.

100Ω

ADL6012

RECEIVER

Z(DIFFERENTIAL) = 100Ω

50Ω

50Ω

VENV+

VENV–

9

8

Figure 61. Simplified ADL6012 Output Interface

–15

–5

5

15

0

2

1

3

4

INPUT POWER (dBm)

OPEN

400Ω

200Ω

100Ω

Figure 62. Differential Envelope Output vs. Input Power for Different Output Loads

The ADL6012 envelope outputs can also be ac-coupled for pulsed

detection applications, as shown in Figure 63. AC coupling allows

different common-mode voltages to be interfaced to the ADC.

For example, the VENV+ and VENV− outputs can be used to

detect pulses in radar applications. See Figure 49 for the typical

envelope pulse response.

PULSED

VPOS

100pF

1µF

+5V

OCOM

EPAD

6

5

RFIN

3

R1

100Ω

C1

1µF

C2

1µF

U3

ADC

IN+

IN–

Figure 63. Simplified Pulsed Measurement Application

COMMON-MODE VOLTAGE INTERFACE

VOCM (Pin 7) is the input that controls the common-mode

voltage output to the VENV± pins. VOCM sets the output

common-mode voltage and is internally biased to VPOS/2.

An external voltage source can be used for setting a different

output common-mode voltage to accommodate the next stage

input common-mode voltage range, as shown in Figure 64. The

reference voltage from the ADC is used as the voltage source to

accurately drive the VOCM pin. The range for VOCM is 0.9 V

to VPOS/2. In addition, this pin is used to level shift the

VENV± outputs so that both the positive and negative

envelope information is accurately represented.

ENBL

RFCM

RFIN

EPAD

DCPL

VENV+

VENV–

R1

100Ω

0.1µF

0.1µF

U3

1

2

10

9

8

ADL6012

3

RFCM

VPOS

VOCM

OCOM

4

7

6

5

ADC

VREF

IN+

IN–

Figure 64. External Voltage Source Setting VOCM

Differential envelope outputs provide the lowest distortion and

lower noise. The advantages of differential outputs include lower

offset error, faster output response, higher common-mode noise

rejection, and less feedthrough. Place a 0.1 µF bypass capacitor

from VOCM to GND to minimize common-mode noise.