Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Nonlinear
Reexamination Certificate
1999-12-22
2001-09-18
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Nonlinear
C324S115000, C324S119000, C324S095000
Reexamination Certificate
active
06291984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to diode power sensors designed to measure power over a wide dynamic range. The present invention further relates to measuring power both within the square law operating range of a diode and outside the square law operating range.
1. Description of the Related Art
Diode power sensors take advantage of a square law operating region of a diode to measure power. The current (I) vs. voltage (V) equation for a diode is typically expressed in an exponentional form according to the equation
I=Io(e
(&eegr;V/kT)
−1) (1)
where Io and &eegr; are constants whose values depend on the details of the diode, T is the diode's temperature in Kelvins and k is Boltsmann's constant.
FIG. 1
shows an ideal I-V curve for a Schottky or PN-Junction type diode following the parameters of equation (1).
A diode's I-V behavior can also be represented in terms of a polynomial series,
I
=
∑
a
n
V
n
(
2
)
where the a
n
values are chosen to suit a particular diode being considered. For a diode receiving a sinusoidal voltage, average current can be calculated using the second order term of equation (2), while other terms of equation (2) can be neglected over a portion of the diode I-V curve. Equation (2) can, thus, be simplified for average sinusoidal current as:
I
avg
=a(V
2
)avg (3)
The portion of the I-V curve where a diode operates according to equation (3) is referred to as the square law region.
A power sensor which measures RMS power can be constructed using a Schottky or PN-Junction diode to take advantage of the I-V square law relation of the diode. RMS power can then be determined by measuring average diode current. Power is determined according to the equation
P=(V
2
)
avg
/2R (4)
where P is average power, and R is the load resistance of typically 50 &OHgr;. Measured average current I
avg
from a diode is related to the average of the square of the diode voltage V according to equation (3), and the average of the square of V is related to average power using equation (4). Therefore average power P can be determined from average diode current I
avg
according to the equation
P=I
avg
/2aR (5)
The power range over which a real diode operates according to the square law is limited. The typical square law operating range for a real diode is approximately −70 dBm to −20 dBm. It is desirable to have a power sensor which can operate over a much greater range.
SUMMARY OF THE INVENTION
In accordance with the present invention, a diode power meter provides a dual mode of operation—a first mode in the square law operating range of the diode, and a second mode where operation is provided continuously through the square law, transition, and linear regions of a diode. The second mode will be referred to herein as a “CW mode”. In accordance with the invention using the first square-law operating mode, power measurements can be over a much greater range than the square-law dynamic range for a single diode. In the CW mode, unmodulated CW signal power can be measured outside the square law operating range of a diode.
A power meter in accordance with the present invention includes multiple diodes to enable measurement of power within a diode square law operating range over a greater range than with a single diode in the first square law mode. A manifold made up of power dividers distributes a signal input to the power meter to the diodes. Different attenuations are provided to each diode so that the square law operating range for each diode covers a different power range. By selecting the appropriate diode output for power measurements, the overall square law operating range for the power meter will be greater than a power meter using a single diode.
The power meter in accordance with the present invention includes a memory map of voltage vs. power in the square law, transition, and linear region of one diode measured for an unmodulated CW input for the CW mode. The diode detector with the least attenuation is the best candidate for measurements in the CW mode since the greater detected output voltage will limit the effect of noise. The map of voltage vs. power enables power to be measured for unmodulated CW signals provided to the power meter which are beyond the square law operating region for the diodes of the power meter.
REFERENCES:
patent: 4943764 (1990-07-01), Szente et al.
Harvey Kenneth C.
Oldfield William W.
Turl Chris
Wong Vincent W. C.
Anritsu Company
Fliesler Dubb Meyer & Lovejoy LLP
Karlsen Ernest
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