Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2001-04-23
2002-06-04
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S184000, C327S531000, C327S104000
Reexamination Certificate
active
06400205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a diode detection circuit, and more particularly, to a diode detection circuit suited for high frequency signal detection.
2. Description of the Related Art
Detection circuits or rectifiers using diodes are known.
FIG. 1
depicts an example of the configuration thereof. A parallel circuit consists of a resistor R
1
and a capacitor C
1
and is connected to the cathode side of a diode D
1
.
When an input signal has a small high-frequency voltage level such as in the case where a diode detection circuit of
FIG. 1
is used to detect the high-frequency signal level between cellular phones and base stations, the forward voltage drop of the diode D
1
will become unnegligible.
That is, the input high-frequency voltage is sagged (voltage dropped) by the forward voltage of the diode D
1
and is output across the resistor R
1
. Due to the nonlinearity in the voltage-current characteristics of the diode D
1
, the detection linearity may become degraded in the minute high-frequency voltage area such as the high-frequency signals between the cellular phones and the base stations.
In addition, the influences of the temperature characteristics of the diode D
1
may cause a large temperature variation in the detection characteristics. The forward voltage fluctuations attributable to the temperature variations may vary depending on the temperature at the rate of about −2 mV/° C., and hence −100 mV output voltage fluctuation will occur by variation of 50° C.
Thus, a diode detection circuit of
FIG. 2
having improved detection linearity and temperature variations was proposed (“Diode Detection Circuit” disclosed in Japan Patent Laid-open Pub. No. Hei7-111421). The diode detection circuit of
FIG. 2
is configured so that an operational amplifier OA
1
offsets the voltage drop and fluctuations of the detection diode D
1
by the voltage drop and fluctuations of a compensation diode D
2
.
The detection diode D
1
and the compensation diode D
2
are correlated with resistors R
1
and R
2
, respectively, so that the ratio of the resistor R
1
to the resistor R
2
conforms to the ratio of the saturation current value of the detection diode D
1
to the saturation current value of the compensation diode D
2
. This allows different types of diodes to be used as the diodes D
1
and D
2
.
FIG. 3
shows another diode detection circuit in which the operational amplifier OA
1
is disposed on the input side of the detection diode D
1
, with the output of the detection diode D
1
being fed back to the negative input of the operational amplifier OA
1
to allow an action as the diode D
1
with zero forward voltage. It is to be noted that if the
FIG. 3
circuit remains unvaried, the circuit output is given in the form of a pulsation current. Similar to the examples of FIGS.
1
and
2
, the addition of the capacitor to the output side enables the high-frequency voltage peak value to be held.
The above circuit of
FIG. 2
aims to relieve the voltage drop and temperature variations of the diode D
1
by rectifying the high-frequency voltage by the diode D
1
and thereafter correcting it by the operational amplifier OA
1
and the diode D
2
.
In this circuit, however, as shown in
FIG. 4
, when the diode D
1
rectifies the high-frequency signals, only a half-cycle current WC
1
flows therethrough whereas the diode D
2
allows a flow of direct current DC
1
therethrough. Thus, the diodes D
1
and D
2
make remarkably different dynamic actions.
As is apparent from
FIG. 5
showing the relationship between the high-frequency voltage WC
1
and the surge current SC, in case of the capacitor input detection circuit as depicted in
FIG. 2
, the surge current SC flows through the diode D
1
for a brief period of time near the peak value of the high-frequency voltage, to charge the capacitor C
1
. Then, gradual discharge is made till the next half cycle (PV in the diagram), and again the charging is effected near the next peak value. These operations are iterated. Accordingly as the mean value of the DC voltage becomes closer to the peak value of the AC voltage WC
1
, the time during which the surge current flows will decrease and the ratio of the surge current SC to the mean direct current becomes larger.
The time rate during which the surge current SC flows depends on the product of the internal resistance of the diode D
1
and the cathode side external capacitance, and will be of the order of {fraction (1/20)} of one cycle. The direct current DC flowing through the diode
2
is about {fraction (1/12)} of the surge current SC.
Therefore, irrespective of the same internal resistances of the diodes D
1
and D
2
, there lies a large difference between the surge current SC and the direct current DC flowing therethrough, with the result that the diodes D
1
and D
2
may disadvantageously suffer different forward voltages.
Another problem lies in that it is difficult to faithfully provide the input high-frequency voltage peak value PV as the DC output.
On the contrary, the circuit of
FIG. 3
is a circuit which is introduced as an ideal diode detection (rectification) circuit, although the high-frequency signals must be amplified by the operational amplifier OA
1
since the output of the operational amplifier OA
1
is rectified by the diode D
1
. It may suffer a further drawback that the operational amplifier OA
1
must have an enough higher (ten times or more) bandwidth than the high-frequency signal to be rectified from the viewpoint of through-rate.
Naturally, good performance of the operational amplifier OA
1
may merely result in an ideal circuit of FIG.
3
. It may not be easy however even to make gain amplification at a high high-frequency voltage of 1 to 2 GHz. In addition, amplification of the high high-frequency voltage of 10 to 20 Ghz with a high gain will lead to significantly increased costs.
As discussed above, the conventional example circuits of
FIGS. 2 and 3
tend to suffer the above respective deficiencies.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to solve the above problem involved in the conventional diode detection circuit and to provide a diode detection circuit capable of obtaining an ideal rectification voltage even in the case of a minute input high-frequency voltage.
In order to achieve the above object, according to an aspect of the present invention there is provided a diode detection circuit comprising a first diode that accepts an AC signal; a first parallel circuit consisting of a resistor and a capacitor, the first parallel circuit accepting a detection output from the first diode; a first operational amplifier having a positive input terminal that accepts a charging voltage for the capacitor of the first parallel circuit; a second diode that accepts an output from the first operational amplifier; a first switching circuit consisting of a first switch and an oscillator, the first switching circuit providing a control of the ratio of conduction to non-conduction of the first and second diodes; a second parallel circuit consisting of a resistor and a capacitor, the second parallel circuit accepting an output from the first switching circuit, with a charging voltage for the capacitor of the second parallel circuit being applied to a negative input terminal of the first operational amplifier; and a holding circuit that holds an output from the first operational amplifier.
Preferably, the diode detection circuit further comprises a second switching circuit disposed on the input side of the holding circuit, the second switching circuit effecting its switching operations alternately with the first switching circuit, and the holding circuit holds a positive peak value of the output from the first operational amplifier.
Preferably, in the diode detection circuit, the holding circuit holds a negative peak value of the output from the first operational amplifier. Preferably, the diode detection circuit further comprises a positive power source exceeding in the f
Nguyen Long
Rosenman & Colin LLP
Tran Toan
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