REV. 0

AD8367

–14–

For an input signal consisting of a 4.096 MS/s QPSK modulated

this setup is shown in Figure 13. The exponential shape reflects

the linear-in-magnitude response of the AD8361. The adjacent

channel power ratio (ACPR) as a function of output power is

illustrated in Figure 14. The minima occur where the distortion

and integrated noise powers cross over.

The component values shown in Figure 12 were chosen for a

64-QAM signal at 500 kS/s at a carrier frequency of 150 MHz.

The response time of the loop as shown is roughly 5 ms for an

abrupt input level change of 40 dB. Figure 15 shows the dynamic

performance of the loop with a step-modulated CW signal applied

POUT – dBm Into 200

4.0

0

3.5

2.0

1.5

1.0

0.5

3.0

2.5

–20

10

–15

–10

–50

5

10MHz

380MHz

Figure 13. AGC Set-Point Voltage vs. Output Power

(QPSK: 4.096 MS/s;

0.22; 1 User)

U1

14

13

12

11

10

9

8

1

2

3

4

5

6

7

ENBL

INPT

MODE

GAIN

DET0

ICOM

ICOM

HPFL

VPSI

VPSO

VOUT

DECL

OCOM

ICOM

AD8367

C5

0.1 F

0.1 F

5V

U2

8

7

6

5

1

2

3

4

SREF

VRMS

FLTR

COMM

VPOS

IREF

RFIN

PWDN

AD8361

10nF

R6

66

RF INPUT

R5

10k

R4

33k

U3

AD820

0.1 F

4

6

7

2

3

5V

C1

3.3nF

R3

82k

20pF

10nF

R1

200

10nF

10nF

R2

150k

12k

Vrms

200

LOAD

C2

0.27 F

Vg

Figure 12. Example of Using an External Detector to Form an AGC Loop

POUT – dBm Into 200

–20

–60

–25

–40

–45

–50

–55

–30

–35

–20

10

–15

–10

–50

5

380MHz

140MHz

10MHz

70MHz

Figure 14. ACPR versus Output Power for QPSK

Waveform (4.096 MS/s;

0.22; 1 User)

TIME – sec

1.0

0

0.5

0.0

–0.5

–1.0

–1.5

–2.0

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

Figure 15. AGC Dynamic Response: 8367 AGC with

an External Detector