CN106932661B - Measuring device with AM modulation function - Google Patents

Abstract

The invention provides a measuring device with AM modulation function, comprising: the input end of the calibration module is the input end of a digital chip; when external modulation is performed, the output end of the calibration module and the input end of the modulation coefficient module are connected by a modulation switch. When performing internal modulation, the output end of the frequency synthesizer is connected to the input end of the modulation coefficient module through the modulation switch; the input end of the baseband bias module is connected to the output end of the modulation coefficient module, and the first end of the baseband bias module is connected to the output end of the modulation coefficient module. An output end is connected with the input end of the combining module, the second output end of the baseband biasing module is connected with the input end of the nonlinear compensation module; the output end of the nonlinear compensation module is connected with the external AM attenuator. Based on the digital AM scheme, the present invention analyzes AM requirements (internal modulation, external modulation and modulation depth, etc.), and proposes a reference scheme for AM implementation in a digital chip combined with the actual performance and calibration requirements of the attenuator.

Description

A measuring device with AM modulation function

technical field

The invention relates to the technical field of signal testing and measurement, in particular to a measurement device with AM modulation function.

Background technique

AM (Aplitude Modulation, Amplitude Modulation) is an important means of wireless communication. Devices such as arbitrary waveform generators and radio frequency signal sources can generate AM signals for use in communication system research or testing. Some arbitrary waveform generators that use analog synthesis and most RF sources implement AM by controlling analog attenuators. Compared with the RF signal source, the frequency of the signal generated by the arbitrary waveform generator is generally lower, and it is mostly used for the pre-research or design of the communication scheme and technology. The frequency of the modulated signal generated by the RF signal source is comparable to the actual range of use, and can be used for research or testing of practical communication equipment and devices. The main function of the radio frequency signal source is to generate radio frequency signals in a certain frequency range and amplitude range, as the excitation or reference of the device under test, and assist in the test and measurement of electronic devices. Amplitude accuracy and stability is one of the important technical indicators of the RF signal source, which is mainly guaranteed by ALC (Automatic Level Control, automatic level control circuit). When AM is turned on, the amplitude of the carrier signal (basic radio frequency signal) of the signal source is also required to remain basically unchanged and to maintain the original stability.

Patent CN201310721663.8 introduces a radio frequency signal source, and its principle block diagram is shown in FIG. 1 . The radio frequency signal source mainly includes a frequency synthesizer 101 , an automatic level control circuit 102 and a step attenuator 103 . The main function of the frequency synthesizer 101 is to generate a radio frequency signal with a frequency set by the user, the automatic level control circuit 102 controls the amplitude accuracy and stability of the radio frequency signal, and the step attenuator 103 uses a relatively large attenuation step to output The amplitude of the signal is further adjusted to expand the amplitude range that the RF signal source can output.

In the radio frequency signal source, AM is implemented in the automatic level control circuit 102 as its extended function. Patent CN201310721663.8 introduces a common analog ALC scheme and its AM implementation, as shown in Figure 2.

The ALC part consists of an adjustable RF attenuator 201, a matching resistor 202, a RF amplifier 203, a directional coupler 204, an exponential amplifier 205, an adder 206, a comparison integrator (composed of a capacitor 207 and an amplifier 208), an adder 209, a logarithm The amplifier 210 , the logarithmic amplifier 211 and the detector 212 are composed. 2A is the input RF signal, 2F is the output RF signal, and 2G is the set reference signal. If the amplitude of the output RF signal 2F is not equal to the amplitude represented by the set reference signal 2G, the output of the comparison integrator (composed of the capacitor 207 and the amplifier 208 ) will change, and it will be amplified by the exponential amplifier 205 as an adjustable RF attenuator. 201 attenuation until the output signal amplitude reaches the set value. The AM modulated signal (baseband signal, 2H) passes through the logarithmic amplifier 211 and then enters the adder 209 and the adder 206 before and after the comparison integrator, respectively, to control the ALC to realize AM.

In the analog ALC scheme, the AM is attached to the ALC and has higher requirements on the tunable RF attenuator.

Aiming at the problems existing in the analog ALC scheme, patent CN201310721663.8 proposes a digital ALC structure and a corresponding AM implementation scheme, as shown in FIG. 3 .

The power divider 802, the detector 803, the digital processing module 804, and the adjustable radio frequency attenuator 801 in the digital chip 806 form a relatively independent digital ALC loop. A modulated RF attenuator 805 implements AM.

In the digital ALC scheme, AM is not attached to ALC, and the requirements for adjustable RF attenuators are not high. However, the composition and connection of AM are only described in hardware, and there is no clear scheme for the realization of AM in digital chips.

SUMMARY OF THE INVENTION

The embodiment of the present invention provides a measurement device with an AM modulation function, and provides a reference solution for implementing AM in a digital chip. The measuring device includes a digital chip for realizing the AM modulation function;

The digital chip includes a calibration module, a frequency synthesizer, a modulation switch, a modulation coefficient module, a baseband bias module, a combining module and a nonlinear compensation module;

The input end of the calibration module is the input end of the digital chip;

When performing external modulation, the output terminal of the calibration module is connected to the input terminal of the modulation coefficient module through a modulation switch; when performing internal modulation, the output terminal of the frequency synthesizer is connected to the input terminal of the frequency synthesizer through a modulation switch. the input terminal of the modulation coefficient module is connected;

The input end of the baseband biasing module is connected to the output end of the modulation coefficient module, the first output end of the baseband biasing module is connected to the input end of the combining module, and the first output end of the baseband biasing module is connected to the input end of the combining module. The two output terminals are connected to the input terminal of the nonlinear compensation module;

The output end of the nonlinear compensation module is connected with an external AM attenuator;

The calibration module is used for calibrating the signal input by the user to obtain the external modulation signal;

the frequency synthesizer is used to generate the internal modulation signal;

The modulation coefficient module is used to change the modulation depth of the outer modulation signal or the inner modulation signal;

The baseband offset module is used to change the offset of the external modulation signal or the internal modulation signal;

The combining module is used to combine the external modulation signal or the internal modulation signal with the ALC reference voltage;

The nonlinear compensation module is used to perform nonlinear compensation on the external modulation signal or the internal modulation signal.

In one embodiment, the calibration module includes a sampling coefficient unit and a sampling offset unit;

The input end of the sampling coefficient unit is the input end of the calibration module, the output end of the sampling coefficient unit is connected with the input end of the sampling offset unit, and the output end of the sampling offset unit is connected with the modulation Toggle switch connection;

Or, the input terminal of the sampling offset unit is the input terminal of the calibration module, the output terminal of the sampling offset unit is connected to the input terminal of the sampling coefficient unit, and the output terminal of the sampling coefficient unit is connected to the input terminal of the sampling coefficient unit. The modulation switch is connected.

In one embodiment, the digital chip further includes a first adder;

The output end of the calibration module and the output end of the frequency synthesizer are simultaneously connected to the first adder through a modulation switch;

A mixed modulation signal is obtained by adding the result of multiplying the inner modulation signal by the inner modulation factor and the result of multiplying the outer modulation signal by the outer modulation factor by the first adder.

In one embodiment, the digital chip further includes a delay module;

The input terminal of the delay module is connected to the output terminal of the baseband bias module, the first output terminal of the delay module is connected to the input terminal of the combining module, and the second output terminal of the delay module is connected to the non-existing terminal. The input terminal of the linear compensation module is connected;

The delay module is used to adjust the phase of the inner modulation signal or the outer modulation signal or the mixed modulation signal.

In one embodiment, the digital chip includes a normalization module;

The input end of the normalization module is connected to the first output end of the delay module, and the output end of the normalization module is connected to the input end of the combining module;

The normalization module is used for normalizing the inner modulation signal or the outer modulation signal or the mixed modulation signal and the ALC reference voltage.

In one embodiment, the normalization module is a logarithmic amplifier, and the combining module is an adder.

In one embodiment, the normalization module is a divider, and the combining module is a multiplier.

In one embodiment, the nonlinear compensation module includes a main wave table unit, a frequency compensation table unit, a first multiplier, a second adder, a temperature compensation unit, and a third adder;

The input end of the main wave table unit is connected with the output end of the delay module, and the input end of the frequency compensation table unit is connected with the output end of the delay module;

The main wavetable module is used for searching in the main wavetable according to the internal modulation signal, the external modulation signal or the mixed modulation signal, to obtain the first table lookup result;

The frequency compensation table unit is used for searching in the frequency compensation table according to the internal modulation signal, the external modulation signal or the mixed modulation signal, to obtain the second table lookup result;

The first multiplier is used to multiply the second look-up table result by the frequency coefficient to obtain the multiplication result;

The second adder is used to add the multiplication result and the first look-up table result to obtain the control voltage;

The temperature compensation unit is used to perform temperature compensation on the control voltage to obtain a temperature compensation voltage;

The third adder is used for adding the temperature compensation voltage and the control voltage to obtain the final control voltage.

In one embodiment, the temperature compensation unit includes a second stage amplifier, a temperature compensation table unit and a second multiplier;

The second-stage amplifier is used for linearly amplifying the control voltage;

The temperature compensation table unit is used for searching in the temperature compensation table according to the linearly amplified control voltage to obtain the temperature compensation result;

The second multiplier is used to multiply the temperature compensation result by the compensation coefficient to obtain the temperature compensation voltage.

In one embodiment, the nonlinear compensation module further includes a first-stage amplifier;

The input end of the first-stage amplifier is the input end of the nonlinear compensation module, and the output end of the first-stage amplifier is connected to the input end of the main wavetable unit, and is used to convert the internal modulation signal or the external modulation signal. Or mixed modulation signal for linear amplification.

In the embodiment of the present invention, based on the digital AM scheme, the AM requirements (internal modulation, external modulation and modulation depth, etc.) are analyzed, and combined with the actual performance and calibration requirements of the attenuator, a reference scheme for the realization of AM in the digital chip is proposed .

Description of drawings

The accompanying drawings described herein are used to provide a further understanding of the present invention, and constitute a part of the present application, and do not constitute a limitation to the present invention. In the attached image:

1 is a schematic diagram of a basic structure of a radio frequency signal source provided by an embodiment of the present invention;

2 is a block diagram of an analog ALC circuit provided by an embodiment of the present invention;

3 is a block diagram of a digital AM circuit provided by an embodiment of the present invention;

4 is a structural diagram of a measurement device with AM modulation function provided by an embodiment of the present invention;

5 is a structural block diagram of a nonlinear compensation module provided by an embodiment of the present invention;

FIG. 6 is a structural diagram of another measurement device with an AM modulation function provided by an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but not to limit the present invention.

In the existing digital ALC scheme, only the composition and connection of AM are described in hardware, and there is no clear scheme for the realization of AM in digital chip for reference. Based on the digital AM scheme proposed by the patent CN201310721663.8, the present invention designs the structure in the digital chip in detail in combination with the actual requirements and calibration of AM, and forms a practical digital AM scheme.

FIG. 4 is a structural diagram of a measurement device with an AM modulation function provided by an embodiment of the present invention. As shown in FIG. 4 , the measurement device includes a digital chip for realizing the AM modulation function;

The digital chip includes a calibration module, a frequency synthesizer 403, a modulation switch, a modulation coefficient module 406, a baseband bias module 407, a combining module and a nonlinear compensation module 411;

The input end of the calibration module is the input end of the digital chip;

When performing external modulation, the output terminal of the calibration module is connected to the input terminal of the modulation coefficient module 406 through a modulation switch; when performing internal modulation, the output terminal of the frequency synthesizer 403 is connected by a modulation switch. connected with the input end of the modulation coefficient module 406;

The input end of the baseband bias module 407 is connected to the output end of the modulation coefficient module 406, the first output end of the baseband bias module 407 is connected to the input end of the combining module, the baseband bias The second output terminal of the module 407 is connected to the input terminal of the nonlinear compensation module 411;

The output end of the nonlinear compensation module 411 is connected to an external AM attenuator;

The calibration module is used for calibrating the signal input by the user to obtain the external modulation signal;

The frequency synthesizer 403 is used to generate an internal modulation signal;

The modulation coefficient module 406 is used to change the modulation depth of the outer modulation signal or the inner modulation signal;

The baseband offset module 407 is used to change the offset of the external modulation signal or the internal modulation signal;

The combining module is used to combine the external modulation signal or the internal modulation signal with the ALC reference voltage;

The nonlinear compensation module 411 is used to perform nonlinear compensation on the external modulation signal or the internal modulation signal.

In specific implementation, the function of the calibration module is to calibrate the non-ideal characteristics of the sampling circuit, that is, when the user inputs the signal specified in the device manual (eg 1Vpp sinusoidal signal), the calibrated signal is the same as the internally generated modulation signal. Specifically, the calibration module may include a sampling offset unit 401 (subtractor) and a sampling coefficient unit 402 (multiplier);

The input terminal of the sampling coefficient unit 402 is the input terminal of the calibration module, the output terminal of the sampling coefficient unit 402 is connected to the input terminal of the sampling offset unit 401, and the output terminal of the sampling offset unit is connected to the input terminal of the sampling offset unit 401. the modulation switch is connected;

Or, the input terminal of the sampling offset unit 401 is the input terminal of the calibration module, the output terminal of the sampling offset unit 401 is connected to the input terminal of the sampling coefficient unit 402, and the sampling coefficient unit 402 has an output terminal. The output end is connected with the modulation switch;

The functions of the sampling offset unit 401 and the sampling coefficient unit 402 are to calibrate the link error (mainly including system design error and device batch consistency error) between the start of user input and the completion of digital sampling, so that the calibration is performed. The resulting signal amplitude is consistent with the standard signal amplitude input by the user. Calibration is completed before the device leaves the factory and is generally only performed once. When used by users, the coefficients of this module are fixed.

The specific structures of the sampling offset unit 401 and the sampling coefficient unit 402 can be adjusted according to specific circuits, and the sampling offset unit 401 and the like can also be eliminated.

During specific implementation, AM needs to realize the function of adjustable modulation frequency and modulation depth, and needs to realize internal modulation and external modulation. Some devices may also have an "internal + external" modulation mode. At this time, the modulation switch can be replaced with a weight calculation switch module and a first adder.

When performing internal modulation, the internal modulation uses the signal generated inside the digital chip as the modulation signal (baseband signal). This modulation signal can be directly generated by DDS (Direct Digital Synthesizer) 403, and the weight calculation switching module simultaneously Set Weight-Inner (Inner Modulation Coefficient) 405 to "1" and Weight-Outer (Outer Modulation Coefficient) 406 to "0".

When performing external modulation, using the modulation signal 4A provided by the user, the calculation switching module sets the weight-inner (inner modulation coefficient) 405 to "0", and the weight-outer (outer modulation coefficient) 406 to "1".

When performing mixed modulation (“inner+outer” mode), the weight calculation switching module simultaneously sets both weight-inner (inner modulation coefficient) 405 and weight-outer (outer modulation coefficient) 406 to “0.5”. In "inside+outside" mode, the modulated signal generated inside the device and the modulated signal provided by the user are multiplied by 0.5 and then added together by the first adder as the final modulated signal (mixed modulated signal or final baseband signal) .

The above-mentioned inner modulation signal and outer modulation signal are both in the form of y=sin(w0*t), where w0 is the modulation frequency. When performing mixed modulation, both the internal source and the external need to generate a modulation coefficient of y=sin(w0*t), and at the same time, set the weight-inner and weight-outer to be "0.5".

In specific implementation, when internal modulation is performed, the internally generated baseband signal is used for subsequent operations; when external modulation is performed, the externally input and calibrated modulation signal is used for subsequent operations; when mixed modulation is performed, the internal modulation signal is multiplied by 0.5 plus external modulation. After the signal is multiplied by 0.5, it enters the subsequent operation.

Subsequent operations include adjusting the depth and offset of the modulated signal. The modulation coefficient module 406 is used to change the modulation depth of the external modulation signal, the internal modulation signal and the mixed modulation signal, and the modulation depth can be adjusted from 0 to 100%. The baseband offset module 407 is used to change the offset of the external modulation signal, the internal modulation signal and the mixed modulation signal, which is convenient for subsequent logic design. The baseband biased signal can be represented by y=1+ma*sin(w0*t), where w0 is the modulation frequency and ma is the modulation depth.

During specific implementation, the digital chip may further include delay modules (408, 410) for adjusting the phase error when AM and ALC cooperate, that is, the phase of the internal modulation signal or the external modulation signal or the mixed modulation signal. According to the actual situation, there may be 1 or 2, or none.

When there is one, the input terminal of the delay module is connected to the output terminal of the baseband biasing module 407 , the first output terminal of the delay module is connected to the input terminal of the combining module, and the second output terminal of the delay module is connected to the nonlinear compensation module 411 input connection.

When there are two, the input of the delay module 408 is connected to the first output of the baseband bias module 407, the output of the delay module 408 is connected to the input of the combining module; the input of the delay module 410 is connected to the baseband bias The second output terminal of the module 407 is connected, and the output terminal of the delay module 410 is connected to the input terminal of the nonlinear compensation module 411 .

During specific implementation, for AM modulation in the ALC loop, the baseband signal (internal modulation signal or external modulation signal or mixed modulation signal) needs to be converted according to the ALC mode before entering the ALC. Therefore, the digital chip further includes a normalization module, the input terminal of the normalization module is connected to the first output terminal of the delay module, and the output terminal of the normalization module is connected to the input terminal of the combining module. end connection.

If the ALC reference is in logarithmic mode (the reference voltage is expressed in units of dB), the normalization module is a logarithmic amplifier. 4C is added, that is, the combining module is an adder, and the added result is used as the final reference voltage of the ALC loop. If the ALC reference is in linear mode (the reference voltage is expressed in units of volts-V), the normalization block needs to be divided by the value of the baseband bias block, and then multiplied by the ALC reference, that is, the combiner block is a multiplier, and the phase The result of the multiplication serves as the final reference voltage for the ALC loop. In linear ALC, if the modulating signal is already centered on "1", the normalization block can be canceled.

Since the design and processing of integers in general digital chips is slightly simpler than that of decimals, it can be considered to multiply the modulated signal by a larger ratio, and then normalize or directly convert it into the final output at the end.

In the specific implementation, in the analog scheme, the nonlinear compensation of the attenuator is performed according to the output signal in the form of dB. The measurement of AM distortion is based on volts (V). As the modulation depth approaches 100%, a 1% change in modulation depth corresponds to a small change in dB at positive AM peaks and a large change at negative peaks. Nonlinear compensation in dB is not very practical for AM, which tends to distort at positive peaks. In the digital AM scheme, a compensation scheme for AM applications, ie, the nonlinear compensation module 411 , can be designed for AM characteristics.

FIG. 5 is a structural block diagram of a nonlinear compensation module provided by an embodiment of the present invention. As shown in FIG. 5 , the nonlinear compensation module 411 includes a main wave table unit 502, a frequency compensation table unit 503, a first multiplier, and a second adder. a temperature compensation unit and a third adder;

The input end of the main wave table unit 502 is connected with the output end of the delay module, and the input end of the frequency compensation table unit 503 is connected with the output end of the delay module;

The main wavetable unit 502 is configured to search in the main wavetable according to the internal modulation signal, the external modulation signal or the mixed modulation signal, and obtain the first table lookup result;

The frequency compensation table unit 503 is configured to search in the frequency compensation table according to the internal modulation signal, the external modulation signal or the mixed modulation signal, and obtain the second table lookup result;

The first multiplier is used to multiply the second look-up table result by the frequency coefficient to obtain the multiplication result;

The second adder is used to add the multiplication result and the first look-up table result to obtain the control voltage;

The temperature compensation unit is used to perform temperature compensation on the control voltage to obtain a temperature compensation voltage;

The third adder is used for adding the temperature compensation voltage and the control voltage to obtain the final control voltage.

During specific implementation, the nonlinear compensation module 411 may further include a first-stage amplifier 501 , the input end of the first-stage amplifier is the input end of the nonlinear compensation module, and the output end of the first-stage amplifier is connected to the main wavetable The input end of the unit is connected, and its function is to convert the input amplitude signal 5A into a wavetable input (look-up table address), which is a linear amplifier. If the input amplitude signal can directly look up the table, then the first stage amplifier 501 may not be.

The working principle of the nonlinear compensation module is as follows:

The input voltage 5A enters the main wave table and the frequency compensation table respectively after passing through the first-stage linear amplifier 501, and the corresponding output is obtained by looking up the table. The frequency compensation table look-up table result is multiplied by the frequency coefficient, and then added with the main wave table look-up table result to obtain the attenuator control voltage 5C without temperature compensation. The uncompensated control voltage 5C will enter the temperature compensation module to obtain the corresponding temperature compensation value, which is added to the uncompensated voltage 5C to obtain the final control voltage 5B.

In specific implementation, the temperature compensation unit is composed of a second stage amplifier 505, a temperature compensation wavetable unit 506 and a second multiplier. The function of the second stage amplifier 505 is to convert the control voltage 5C to be compensated into the input of the temperature-compensated wavetable (look-up table address). After looking up the table, an initial compensation voltage will be obtained. Multiply to get the final temperature compensation voltage.

In specific implementation, the AM attenuator nonlinear compensation module is used to convert the input signal expressed in volts (V) into the actual control voltage of the attenuator, which needs to compensate the frequency error and temperature error of the attenuator. The input 5A can be represented by y=A*(1+sinw0t), and the output 5B is the control voltage of the attenuator at the corresponding frequency and temperature. The attenuator error is measured in volts (V), based on a fixed voltage value, and the error is larger when the required voltage value is significantly different from the reference value. The nonlinear compensation module relies on the main wavetable to compensate the nonlinearity at one frequency well, and then uses the frequency compensation module to compensate the control voltage of different frequencies at a specific temperature. After the frequency compensation is completed, the result enters the temperature compensation module. Perform temperature compensation. The temperature compensation module and the frequency compensation module are not set in parallel, because the part of the voltage added during frequency compensation also has temperature error, and temperature compensation is also required.

The basic setting of frequency compensation is that the attenuation-control voltage curve changes uniformly at different frequencies. That is, if the attenuation amount-control voltage curve of the attenuator at the frequency freq1 can be represented by the function y=f1(x), (y is the attenuation amount, x is the control voltage), the curve at the frequency freq2 can be expressed as y=f2(x ), then the curve of the function at other frequencies can be represented by the function y=*f1(x)+kf*(f2(x)-f1(x)), where kf is an undetermined frequency compensation coefficient, which changes with frequency. When performing frequency compensation, it is necessary to first scan the attenuation-control voltage relationship for the attenuator at two frequencies (freq1, freq2), and take the curve at one frequency (reference frequency, freq1) as the main wavetable (502) content, The error between the curve at another frequency (reference frequency, freq2) and the curve at the previous frequency (control voltage difference at the same attenuation) is the content of the frequency compensation wavetable (503). The frequency coefficients (504) at different frequencies are obtained by calibration.

The basic setting of temperature compensation is similar to that of frequency compensation, that is, the control voltage changes uniformly with temperature under the same attenuation, but the speed at which the control voltage changes with temperature is related to the attenuation and frequency. The temperature characteristic of the attenuator is compensated using the function y=y0 +m(freq)*(T-T0)*g(y0), and the temperature coefficient (507) contains the product of m(freq) and (T-T0). Among them, the input is the control voltage (y0) without compensation (reference temperature, T0), and the output is the control voltage at the current temperature (T) and frequency (freq); m(freq) is the frequency factor, which changes with frequency; g(y0) is an attenuation compensation factor, which is related to the control voltage (attenuation). During temperature compensation, it is necessary to first measure the attenuation-control voltage curve of the attenuator at different temperatures. Then calculate the temperature error of the attenuation-control voltage curve at the frequency of the main wavetable (reference frequency, freq1), and normalize it to 1 degree Celsius to obtain the basic temperature error. Next, the abscissa (attenuation amount) of the base temperature error is converted into the control voltage at the reference temperature (T0). Finally, linearize the control voltage-basic temperature error curve to the abscissa (control voltage) to obtain a temperature error wavetable. The calculation of the frequency factor can be obtained by calculating the basic temperature error proportional coefficient corresponding to the same attenuation (or control voltage) at different frequencies, or by measuring it by means of a temperature test.

The present invention also proposes an embodiment of a digital AM solution. As shown in FIG. 6 , a test register 611 is added after the nonlinear compensation module 610 .

The working principle is:

After being calibrated by the sampling offset unit 601 and the sampling coefficient unit 602, the user input signal 6A is used as one input of the modulation switch 604, and the modulation signal generated by the internal source 603 is used as another input. The modulation switch 604 realizes the switching of internal/external modulation, the modulation coefficient module 605 realizes the modulation depth change, and the baseband bias module 606 realizes the offset of the modulation signal. The ALC in linear mode needs to divide the baseband signal after the delay block 607 by the baseband offset 608 and then multiply it with the ALC reference DAC. The ALC in logarithmic mode needs to logarithmically amplify the baseband signal after the delay module 607, and then add it to the ALC reference DAC after being amplified by an appropriate linear magnification. The baseband signal (internal modulation signal or external modulation signal or mixed modulation signal) adjusted by the baseband bias module 606 needs to pass through the delay module 609 and the nonlinear compensation module 610 to output signal 6B for controlling the external AM attenuator.

The function of the test register 611 is: when the test mode is enabled, the value of the test register 611 is directly used to control the attenuator to help test the performance of the attenuator.

The effect that the present invention obtains is:

When the frequency temperature compensation is not performed on the attenuator, if the AM carrier frequency changes, the AM positive and negative peak deviation after demodulation can reach more than 10%. After using the frequency and temperature compensation scheme in logarithmic mode, the AM distortion is calibrated, and the positive and negative peak errors under different carrier frequencies can be within 3%. However, the peak error changes drastically with temperature, the modulation depth is set to 90%, the temperature changes by about 5 degrees Celsius, and the positive peak value changes by about 7%. Using the compensation scheme of the present invention, -5 to 55 degrees Celsius, 100% debugging depth, and the variation of positive and negative peak errors is less than about 5%.

Obviously, those skilled in the art should understand that each module or each step of the above-mentioned embodiments of the present invention may be implemented by a general-purpose computing device, and they may be centralized on a single computing device, or distributed in multiple computing devices. network, they can optionally be implemented with program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, and in some cases, can be different from the The illustrated or described steps are performed in order, either by fabricating them separately into individual integrated circuit modules, or by fabricating multiple modules or steps of them into a single integrated circuit module. As such, embodiments of the present invention are not limited to any particular combination of hardware and software.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, various modifications and changes may be made to the embodiments of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. a measuring device with AM modulation function is characterized in that, the measuring device comprises a digital chip for realizing AM modulation function; The digital chip includes a calibration module, a frequency synthesizer, a modulation switch, a modulation coefficient module, a baseband bias module, a combining module and a nonlinear compensation module; The input end of the calibration module is the input end of the digital chip; When performing external modulation, the output terminal of the calibration module is connected to the input terminal of the modulation coefficient module through a modulation switch; when performing internal modulation, the output terminal of the frequency synthesizer is connected to the input terminal of the frequency synthesizer through a modulation switch. the input terminal of the modulation coefficient module is connected; The input end of the baseband biasing module is connected to the output end of the modulation coefficient module, the first output end of the baseband biasing module is connected to the input end of the combining module, and the first output end of the baseband biasing module is connected to the input end of the combining module. The two output terminals are connected to the input terminal of the nonlinear compensation module; The output end of the nonlinear compensation module is connected with an external AM attenuator; The calibration module is used for calibrating the signal input by the user to obtain the external modulation signal; the frequency synthesizer is used to generate the internal modulation signal; The modulation coefficient module is used to change the modulation depth of the outer modulation signal or the inner modulation signal; The baseband offset module is used to change the offset of the external modulation signal or the internal modulation signal; The combining module is used to combine the external modulation signal or the internal modulation signal with the ALC reference voltage; The nonlinear compensation module is used to perform nonlinear compensation on the external modulation signal or the internal modulation signal. 2. The measuring device with AM modulation function as claimed in claim 1, wherein the calibration module comprises a sampling coefficient unit and a sampling offset unit; The input end of the sampling coefficient unit is the input end of the calibration module, the output end of the sampling coefficient unit is connected with the input end of the sampling offset unit, and the output end of the sampling offset unit is connected with the modulation Toggle switch connection; Or, the input terminal of the sampling offset unit is the input terminal of the calibration module, the output terminal of the sampling offset unit is connected to the input terminal of the sampling coefficient unit, and the output terminal of the sampling coefficient unit is connected to the input terminal of the sampling coefficient unit. The modulation switch is connected. 3. The measuring device with AM modulation function as claimed in claim 1, wherein the digital chip also comprises a first adder; The output end of the calibration module and the output end of the frequency synthesizer are simultaneously connected to the first adder through a modulation switch; A mixed modulation signal is obtained by adding the result of multiplying the inner modulation signal by the inner modulation factor and the result of multiplying the outer modulation signal by the outer modulation factor by the first adder. 4. the measuring device with AM modulation function as claimed in claim 3, is characterized in that, also comprises delay module in described digital chip; The input terminal of the delay module is connected to the output terminal of the baseband bias module, the first output terminal of the delay module is connected to the input terminal of the combining module, and the second output terminal of the delay module is connected to the non-existing terminal. The input terminal of the linear compensation module is connected; The delay module is used to adjust the phase of the inner modulation signal or the outer modulation signal or the mixed modulation signal. 5. The measuring device with AM modulation function as claimed in claim 4, wherein the digital chip comprises a normalization module; The input end of the normalization module is connected to the first output end of the delay module, and the output end of the normalization module is connected to the input end of the combining module; The normalization module is used for normalizing the inner modulation signal or the outer modulation signal or the mixed modulation signal and the ALC reference voltage. 6 . The measuring device with AM modulation function according to claim 5 , wherein the normalization module is a logarithmic amplifier, and the combining module is an adder. 7 . 7 . The measuring device with AM modulation function according to claim 5 , wherein the normalization module is a divider, and the combining module is a multiplier. 8 . 8. The measuring device with AM modulation function according to claim 4, wherein the nonlinear compensation module comprises a main wave table unit, a frequency compensation table unit, a first multiplier, a second adder, a temperature compensation unit and third adder; The input end of the main wave table unit is connected with the output end of the delay module, and the input end of the frequency compensation table unit is connected with the output end of the delay module; The main wavetable unit is used for searching in the main wavetable according to the internal modulation signal, the external modulation signal or the mixed modulation signal, to obtain the first table lookup result; The frequency compensation table unit is used for searching in the frequency compensation table according to the internal modulation signal, the external modulation signal or the mixed modulation signal, to obtain the second table lookup result; The first multiplier is used to multiply the second look-up table result by the frequency coefficient to obtain the multiplication result; The second adder is used to add the multiplication result and the first look-up table result to obtain the control voltage; The temperature compensation unit is used to perform temperature compensation on the control voltage to obtain a temperature compensation voltage; The third adder is used for adding the temperature compensation voltage and the control voltage to obtain the final control voltage. 9. The measuring device with AM modulation function as claimed in claim 8, wherein the temperature compensation unit comprises a second stage amplifier, a temperature compensation table unit and a second multiplier; The second-stage amplifier is used for linearly amplifying the control voltage; The temperature compensation table unit is used for searching in the temperature compensation table according to the linearly amplified control voltage to obtain the temperature compensation result; The second multiplier is used to multiply the temperature compensation result by the compensation coefficient to obtain the temperature compensation voltage. 10. The measuring device with AM modulation function according to claim 8, wherein the nonlinear compensation module further comprises a first-stage amplifier; The input end of the first-stage amplifier is the input end of the nonlinear compensation module, and the output end of the first-stage amplifier is connected to the input end of the main wavetable unit, and is used to convert the internal modulation signal or the external modulation signal. Or mixed modulation signal for linear amplification.

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