Phase Detectors
The figure-of-merit M or efficiency of a phase detector can be defined as the ratio of maximum
DC output voltage (in mV) divided by the RF power (in dBm). The maximum DC output from
these units is 1000 mV with +7 dBm applied to the LO and RF ports. Thus, its figure-of-merit M
is 143, which indicates a highly efficient phase detector. DC offset is typically 400 micro volts.
For comparison, a double balanced mixer used as a phase detector of offers 350 mV DC output
with the same LO and RF inputs for a figure-of-merit M of 50. So when your system requires a
high output phase detector, specify Mini-Circuits' phase detectors, available in a wide variety of
package styles.
dc offset
The small amount of voltage present at the output when there should actually be zero voltage,
such as when only one input is present, or when the two RF input signals are 90o out of phase.
This offset voltage is due to slight mismatches in the diodes and/or imperfect balance in the
transformer windings.
maximum dc output
from a phase detector occurs when the RF and LO signals are in phase or 180 degrees
out-of-phase.
figure-of-merit, M
A method for defining the efficiency of a phase detector. It is the ratio of maximum DC output
voltage, in mV, divided by the RF power in dBm.
frequency range spec
Refers to the frequency range of operation of the phase detector, such that the figure of merit
decreases to 75 percent of its mid-band value.
scale factor
The phase detector output measured in mV per degree in the approximate linear range of
operation, 0 to 57.3o , or 1 radian.
Last Updated: 09/08/1999