For price, delivery and to place orders: Hittite Microwave Corporation, 2 Elizabeth Drive, Chelmsford, MA 01824

Phone: 978-250-3343

Fax: 978-250-3373

Order On-line at www.hittite.com

Application Support: Phone: 978-250-3343 or apps@hittite.com

21

HMC992LP5E

v03.1013

IF AUTOMATIC GAIN CONTROLLER

(IF-AGC), 50 - 800 MHz

Log Detector

The logarithmic detector of the HMC992LP5E converts the average envelope of RF input power to a proportional DC

voltage at its output (DETOUT), as shown in Figure 8. In detection mode, the DETOUT pin should be connected to

the VSET input. The HMC992LP5E’s logarithmic detector employs a successive compression technology which deliv-

ers 50 dB of dynamic range (±1dB) with high conversion accuracy over a wide input frequency range. Note that the

link between DETOUT and VCTRL pins must broken and DETOUT must connected to VSET via 1k Ohms resistor for

LOGAMP operation.

The HMC992LP5E’s logarithmic detector can be used in the controller mode where an external voltage is applied to the

VSET pin to create an AGC loop. The linear-in-dB behavior of the HMC992LP5E’s VGA and logarithmic detector creates

a linear AGC system. For linear operation, the signal fluctuations at the input of the log detector should remain within

the dynamic range of the log detector. In closed loop AGC operation, the HMC992LP5E’s response to large input level

changes is not slew-rate limited, and the speed of the transient response can be adjusted through loop filter capacitors

C28 and C30 (see Figure 5).

To achieve maximum gain adjustment range of the HMC992LP5E, the coupler ratio should be chosen based on the

output power desired. A coupler ratio which translates the output power to the center (-25dBm) of the usable dynamic

range of the log detector should be chosen. The gain adjustment range of the HMC992L5E is maximized in this con-

figuration. If the linear operation range of the HMC992LP5E is maximized by selecting the appropriate coupler ratio, the

HMC992LP5E can handle larger changes in input level. For example, an input voltage of 0.6 V is applied to the Vset

pin to set the constant output power level to -13 dBm. A coupler ratio of ~12 dB can be chosen to provide a maximum

dynamic range of 46 dBm.

Figure 8: DETOUT vs. input power over frequency.

0

0.3

0.6

0.9

1.2

1.5

-70

-60

-50

-40

-30

-20

-10

0

10

100 MHz

300 MHz

500 MHz

800 MHz

INPUT POWER (dBm)

Information furnished by Analog Devices is believed to be accurate and reliable. However, no

responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

rights of third parties that may result from its use. Specifications subject to change without notice. No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Trademarks and registered trademarks are the property of their respective owners.

For price, delivery, and to place orders: Analog Devices, Inc.,

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106

Phone: 781-329-4700 • Order online at www.analog.com

Application Support: Phone: 1-800-ANALOG-D