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HMC993LP5E

v00.0911

RF AUTOMATIC GAIN CONTROLLER

(RF-AGC), 700 - 3000 MHz

uation levels of the variable attenuators, the noise contribution from the VGA is less important and the noise requirement

of the VGA is relaxed since the input signal is high. The noise figure performance of the HMC993LP5E’s VGA at 1900

MHz is shown in Figure 4. The HMC993LP5E’s VGA delivers a noise figure of 9.8 dB in its maximum gain state when it

is configured in 1 attenuator + 2 amplifiers mode.

For low attenuation levels of the variable attenuators, IIP3 is less important since high gain of whole VGA improves dis-

tortion performance at its output (OIP3). For high attenuation levels of the variable attenuators, IIP3 is more important

because of low gain of whole VGA. The distortion performance of the HMC993LP5E’s VGA at 1900 MHz is shown in

Figure 4. The HMC993LP5E’s VGA provides an almost constant OIP3 of up to +45 dBm in any state when it is config-

ured in one attenuator and two amplifiers mode.

Figure 4: Noise Figure & Gain & OIP3 vs. VCTRL at 1900 MHz, 1 attenuator.

0

10

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40

50

1

1.5

2

2.5

3

3.5

4

Noise Figure

Gain

0

10

20

30

40

50

OIP3

VCTRL (V)

AGC Operation

The HMC993LP5E can be configured as an AGC amplifier by using VGA core and the built in log detector. An example

for AGC amplifier configuration of the HMC993LP5E is depicted in Figure 5.

In AGC amplifier configuration, the input signal is amplified by the HMC993LP5E’s VGA.The output of the HMC993LP5E’s

VGA core is fed back to the input of the HMC993LP5E’s log detector (RFDETIN) through an external coupler or attenu-

ator to drop the maximum and minimum output level of the HMC993LP5E’s VGA to within the dynamic range of the

HMC993LP5E’s log detector. The HMC993LP5E’s log detector produces a voltage at the output of the log detector

(DETOUT) proportional to the output power level of the HMC993LP5E’s VGA. The high impedance output pin DETOUT

is connected to the gain control pin VCTRL of VGA to form the AGC loop. The VSET pin is the constant output power set

point of the AGC amplifier. As a result of negative feedback, the gain of the VGA is automatically adjusted to maintain a

constant signal power level at the output of AGC amplifier. The output signal power level is determined by the AGC set

point VSET, regardless of the input signal variation.

AGC Set point Interface VSET

In closed loop AGC operation the output power level of the HMC993LP5E is controlled by the VSET pin. An input volt-

age between 0.2V and 1.2V should be applied to the VSET input pin to control the output power level. Output power vs.

VSET characteristic is shown in Figure 6a and Figure 6b for different input power levels and different coupler ratios used.

The slope of the gain vs. VSET characteristic is 58.3dB/V and it is independent of the coupler ratio used.

The relation between the gain of HMC993LP5E’s output power and VSET pin voltage at 1900 MHz can be approximated

as given in Equation (1) when it is configured in AGC amplifier configuration with 2 attenuator + 2 amplifiers.

Output Power (dBm) = -67.7 + |Coupler Ratio| + 58.3 x VSET

Equation (1)