Because diode has rectification characteristic and use generation volts d.c. , and want existence diode only, the volts d.c. that its produce becomes scale with communication and RF signal n.

 

The content that shares for everybody today replaces the RF that is based on diode and microwave product and integrated circuit the product is compared relatively.

 

Be based on the radiodetector of schism type RF of diode

 

Graph 1 those who show is use extensively, the graph of principle of RF demodulation circuit that is based on diode. Can regard it as those who contain output filter wave is simple and easy half commutator. Input signal half-period to slant buy Xiaoteji diode, charge to capacitance then. When negative half-period, diode slants reversely buy, the tension that causes capacitance to go up is in hold position, generation and dc of input signal proportionate are outputted. Drop to this voltage lets when input signal drops or closing, the shunt-wound combination that uses resistor and electric capacity will offer discharge way.

 

Graph 1. The Xiaoteji that is based on diode RF radiodetector

 

Graph the 2 transfer function that displayed this circuit. Power input is adjusted for the unit with DB, output voltage with logarithm perpendicular scale expresses. Observe 25°C transfer function, discovery has two different job interval on the curve. The top that calls the area of linear interval to be input limits (make an appointment with 15 DBm) to arrive about 0 DBm. ” of term “ linear interval is become scale roughly as a result of the output voltage inside this area and input voltage and get a name.

 

Graph 2. The Xiaoteji that is based on diode RF radiodetector transfer function

 

0 DBm is section of law of so called square below. Inside this area, output voltage becomes scale with the square that inputs voltage roughly. The slope that this brings about a curve is taller.

 

Graph 2 still showed –40°C is mixed + the relation of the circuit output voltage below 85°C temperature and power input transfer function. It shows the power n error under 0 DBm is bigger. This makes parts of an apparatus becomes not stable in the application with temperature largish change.

 

Have a few technologies can going up somehow alleviate temperature drift. These technologies include to introduce the 2nd referenced diode to serve as the one part of circuit, perhaps serve as independent circuit, have independent output. The temperature drift of referenced diode and advocate diode matchs. Handle through subtration (imitate region or digital region, circuit structure decides specific basis) , drift can be eliminated on certain level.

 

Graph the 3 compositive pattern that showed ADL6010—— is based on diode radiodetector of Xiao Te radical, have many innovation character —— the transfer function when 25 GHz. Regard signal as the one part of processing, the ability when input signal passes to be made the same score under specific power cable in signal only carries out the circuit that square root operates. Transition nods intended setting to come from transition of square law interval to be equal to diode the power n of linear interval. Accordingly, the square law effect of diode is able to eliminate, and the transfer function of two interval also is inferior to a graph 1 so apparent.

 

Graph 3. When 25 GHz compositive type the output voltage of diode radiodetector and power input mix Xiaoteji the relation of error of degree of linearity

 

Graph 3 still showed arrive from –55°C + the transfer function curve of all sorts of temperature inside 125°C limits. Additional, return line out the change that transfer function produces along with temperature. Serve as the linear regression of 25°C transfer function fiducial, it is the error that each temperature leaves unit line out with DB. Because compositive type temperature compensates circuit and smooth square law to remove the effect of circuit, can see the majority scope that inputting inside, degree of linearity and the error that temperature drift produces are ±0.5 DB about.

 

 

Although can be in occasionally,operating ring of imitate power source uses RF and microwave radiodetector in the road, but more general is compose builds operating ring of power source of a number road, if pursue,4 are shown. In these application, the output of power radiodetector uses modulus converter to undertake digitlizing handling. In several field, use the code that comes from ADC to calculate power n. Once obtained power n, the system can be made answer, by need to adjust transmission power.

 

Graph 4. Operating ring of typical power of numerical control RF road

 

Although the noise of this annulus road is in season rely on radiodetector to answer time on less degree only, but ADC sampling rate and the impact that power controls algorithmic rate can be gotten greatly much.

 

Annulus road is measured and the ability that installs RF power n accurately suffers a series of element effects, include the transfer function of RF radiodetector and ADC resolution. To understand this better, make us farther see the response of radiodetector. Graph the response when 20 GHz and HMC1094 of microwave logarithm amplifier undertake the 5 radiodetector ADL6010 that will be based on diode comparative. Logarithm amplifier has the transfer function of linear DB, the 1 DB change of its power input brings about output end to have identical voltage to change from beginning to end (about –50 DBm inputs limits) to the linear of 0 DBm. Under photograph comparing, below the case that uses DB scale and linear x-axis to be used at outputting voltage in cross axle, the such as ADL6010 radiodetector that is based on diode has the transfer function of exponential form.

 

Graph 5. Linear DB is comparative

 

It is as a result of the transfer function unit of modulus converter / voltage, this is meant with DB/ denotive system resolution can drop as the fall of power input ceaselessly. Graph 5 medium curves still showed / DB resolution, but by ADL6010 with drive of voltage of 5 V full span a 12 ADC implementation (examine to go to the lavatory, this curve labels with logarithm layshaft scale) . –25 DBm place is arranged in the low end of limits of power of parts of an apparatus, increase by degrees slope is every DB2 about, make resolution is 0.5 DB/ about thereby. This states accurate inside full span limits analytic ADL6010 outputs a 12 ADC enough.

 

As RF the addition of power input, with / DB is an unit increase by degrees slope general falls to rise to steadily in the biggest power input of 15 DBm about 300 / the maximum of DB. This controls application to RF power and character is valuable; Achieve when the system most when high-power, the precision function of this kind of application is crucial. RF radiodetector is used measure and control high power amplifier (the applied setting that HPA) is a special typical case. Often need to control power in those in case in the application of HPA overheat, with most high-power undertakes high resolution power measures measure to have huge value.

 

Under photograph comparing, graph transfer function of 5 medium HMC1094 logarithm amplifier still show it the slope inside linear work limits is changeless. If want to come true,this is meant far the resolution under 1 DB, the ADC (10 that uses inferior resolution even 8) enough.

 

In the graph in 6 indication application circuit, ADL6010 and AD7091 butt joint, latter is a 12 nicety ADC, sampling rate is top for 1 MSPS. Source of fiducial voltage of 2.5 V of the buy inside this ADC, can install full span to input voltage. Because ADL6010 radiodetector is accessible the biggest voltage is 4.25 V about, use a simple resistor voltage divider to be able to adjust this voltage downward, make its never exceed 2.5 V thereby. It is OK that this kind adjusts deploy is finished below the circumstance that does not have operation amplifier bumper. The DB/ that office of floor of power input limits can realize resolution and above paragraphs give a demonstration are similar (namely about 0.5 DB/ ) .

 

Graph 6. Radiodetector of power of compositive type microwave and accurate ADC interface

 

 

Compare with photograph of schism type deploy, compositive type RF and microwave demodulation appliance have numerous advantage ——

 

Compensation circuit offers compositive type temperature to be used namely model output voltage, its can be stabilized inside wide temperature limits control in ±0.5 DB;

The square law when using function of in-house square root to be able to eliminate n of low power input effectively is characteristic, can have individual and linear transfer function so, make calibration of parts of an apparatus more convenient;

The amortize of compositive type radiodetector outputs ADC of OK and direct drive, need not fear laden meeting affects computational precision. (when choice and design ADC must careful, so that be below low power input,have enough / DB) book.