HMC992LP5E Datasheet, PDF (21/22 Pages) Hittite Microwave Corporation – IF AUTOMATIC GAIN CONTROLLER (IF-AGC), 50 - 800 MHz

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HMC992LP5E
IF AUTOMATIC GAIN CONTROLLER
(IF-AGC), 50 - 800 MHz
8
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.
1.5
1.2
100 MHz
300 MHz
500 MHz
800 MHz
0.9
0.6
0.3
0
-70 -60 -50 -40 -30 -20 -10
0
10
INPUT POWER (dBm)
Figure 8: DETOUT vs. input power over frequency.
8 - 21
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