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Due to part-to-part variations in log-slope and log-intercept, a system-level calibration is recommended to satisfy
absolute accuracy requirements. When performing this calibration, choose at least two test points: near the top-end
and bottom-end of the measurement range. It is best to measure the calibration points in the regions (of frequency and
amplitude) where accuracy is most important. Derive the log-slope and log-intercept, and store them in non-volatile
memory. Calibrate iPAR scaling by measuring the peak-to-average ratio of a known signal.
For example if the following two calibration points were measured at 2.35 GHz:
With Vrms = 2.34V at Pin = -7dBm,
and Vrms=1.84V at Pin = -16dBm
Slope Calibration Constant = SCC
SCC = (-16+7)/(1.84-2.34) = 18 dB/V
Intercept Calibration Constant = ICC
ICC = Pin – SCC*Vrms = -7 – 18.0 * 2.34 = -49.12dBm
Now performing a power measurement:
Vrms measures 2.13V
[Measured Pin] = [Measured Vrms]*SCC + ICC
[Measured Pin] = 2.13*18.0 – 49.12 = -10.78dBm
An error of only 0.22dB
Factory system calibration measurements should be made using an input signal representative of the application. If
the power detector will operate over a wide range of frequencies, choose a central frequency for calibration.
Layout Considerations
Mount RF input coupling capacitors close to the IN+ and IN- pins.
Solder the heat slug on the package underside to a grounded island which can draw heat away from the die
with low thermal impedance. The grounded island should be at RF ground potential.
Connect power detector ground to the RF ground plane, and mount the supply decoupling capacitors close
to the supply pins.
Definitions:
Log-slope: slope of PIN –> VRMS transfer characteristic. In units of mV/dB
Log-intercept: x-axis intercept of PIN –> VRMS transfer characteristic. In units of dBm.
RMS Output Error: The difference between the measured PIN and actual PIN using a line of best fit.
[measured_PIN] = [measured_VRMS] / [best-fit-slope] + [best-fit-intercept], dBm
Input Dynamic Range: the range of average input power for which there is a corresponding RMS output
voltage with “RMS Output Error” falling within a specific error tolerance.
Crest Factor: Peak power to average power ratio for time-varying signals.
System Calibration
HMC714LP5 / 714LP5E
v07.1109
DUAL RMS POWER DETECTOR
0.1 - 5.8 GHz