HMC714LP5 Datasheet, PDF (33/40 Pages) Hittite Microwave Corporation – DUAL RMS POWER DETECTOR 0.1 - 3.9 GHz

v05.0309
HMC714LP5 / 714LP5E
DUAL RMS POWER DETECTOR
0.1 - 3.9 GHz
12
RMS Output Interface and Transient Response (Continued)
Transient response can also be slewed by the RMS output if it is excessively loaded: keep load resistance above
375Ω. An optimal load resistance of approximately 500Ω to 1kΩ will allow the output to move as quickly as it is able.
For increased load drive capability, consider a buffer amplifier on the RMS output.
Using an integrating amplifier on the RMS output allows for an alternative treatment for faster settling times. An external
amplifier optimized for transient settling can also provide additional RMS filtering, when operating HMC714LP5E with
a lower C_INT capacitance value.
Rise/Fall Characteristics, CINT = 0 pF
4
3.5
10 dBm
0 dBm
3
-10 dBm
-20 dBm
2.5
-30 dBm
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
3
TIME (usec)
Rise/Fall Characteristics, CINT = 10 nF
4
3.5
10 dBm
0 dBm
-10 dBm
3
-20 dBm
-30 dBm
2.5
2
1.5
1
0.5
0
0
50
100
150
200
250
TIME (usec)
LOG-Slope and Intercept
The HMC714LP5E provides for an adjustment of output scale by controlling the fraction of RMS_A/RMS_B that is
fed-back to the setpoint interface at the V_SETA/V_SETB pins. Log-slope and intercept can be adjusted to “magnify” a
specific portion of the input sensing range, and to fully utilize the dynamic range of the RMS output.
A log-slope of 36.5 mV/dBm is set by connecting the RMS_A/RMS_B outputs directly to V_SETA/V_SETB pins using
0Ω resistors RFBK_A and RFBK_B. The log-slope is adjusted by using the appropriate resistors RFBK_A, RFBK_B,
RSHUNT_A, RSHUNT_B on the RMS_A/RMS_B and V_SETA/V_SETB pins. Log-intercept is adjusted by applying a DC
voltage to the V_SETA/V_SETB pins through resistors R_SETA and R_SETB .
Due to the 15 kΩ input resistance at the V_SETA/V_SETB pins, moderately low resistance values should be used to
minimize the scaling errors. Very low resistor values will reduce the load driving capabilities of RMS_A/RMS_B outputs
while larger values will result in scaling errors and increase of the temperature errors because of the mismatch of
the on-chip and external resistor temperature coefficients.
12 - 146
Optimized slope = ß * log slope
Optimized intercept = log intercept - (R / R ) * Vzc
FBK
SET
R
FBK
ß=
R // R // R
FBK
SHUNT
SET
When R = 0 Ohm to set RMS = V , then ß = 1
FBK
SET
Note: Avoid excessive loading of the RMS output; keep
C < 35 pF, and R > 375Ω
LOAD
LOAD
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