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26

HMC993LP5E

v00.0911

RF AUTOMATIC GAIN CONTROLLER

(RF-AGC), 700 - 3000 MHz

detector, a high enough coupler ratio should be chosen to translate the maximum VGA output power level to a value

lower than the highest detectable log detector power level.

Similarly, the lower side of the dynamic range is limited by the noise floor of the VGA or the lowest power level detect-

able by the log detector. To eliminate any limitations on the lower side of the dynamic range, the coupler ratio should be

low enough to translate the minimum VGA output power level to a value higher than the lowest detectable log detector

power level.

Please also refer to the Log Detector section for more information.

Figure 7a shows the output power vs. input power transfer characteristic of the HMC993LP5E over different VSET

voltages for a closed AGC loop configuration. For low and high input power levels the HMC993LP5E attenuation rage

is saturated and the output is a linear function of the input. For input power levels within the dynamic range, the

HMC993LP5E automatically adjusts the attenuation level as shown in Figure 7b to maintain a constant output power

level. When Vset=0.5 V, the output power level is set to -18.7 dBm and the HMC993LP5E’s AGC amplifier provides a

gain control range of 33.6 dB from -40.2 dBm to -6.6 dBm with an excellent ripple within 0.7 dB.

Figure 7a: Output Power vs. input power over VSET,

2 attenuators @ 1900 MHz.

Figure 7b: DETOUT vs. input power over VSET, 2

attenuators @ 1900 MHz..

-40

-30

-20

-10

0

-60

-50

-40

-30

-20

-10

0

10

VSET=0.3V

VSET=0.5V

VSET=0.7V

INPUT POWER (dBm)

20 dB coupler is used

0

1

2

3

4

5

-60

-50

-40

-30

-20

-10

0

10

Vset = 0.3V

Vset = 0.5V

Vset = 0.7V

INPUT POWER (dBm)

20 dB coupler is used

Log Detector

The logarithmic detector of the HMC993LP5E 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 HMC993LP5E’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 HMC993LP5E’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 HMC993LP5E’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 HMC993LP5E’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

C4 and C7 (see Figure 5).

To achieve maximum gain adjustment range of the HMC993LP5E, 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