CN102638228A - Up-converter and up-conversion method - Google Patents
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Abstract
The invention provides an up-converter and an up-conversion method. The up-converter comprises a double-path digital-to-analog converter for converting an input baseband signal into two paths of orthogonal mid-frequency and low-frequency signals and outputting the two paths of orthogonal mid-frequency and low-frequency signals, and an analog orthogonal modulator for receiving the two paths of orthogonal mid-frequency and low-frequency signals, modulating the two paths of orthogonal mid-frequency and low-frequency signals into mid-frequency signals by using a local oscillation signal of a first oscillator in the up-converter and outputting the mid-frequency signals. According to the up-converter and the up-conversion method, the volume of the up-converter, the circuit complexity and the implementation cost are reduced; and furthermore, the analog orthogonal modulator replaces a frequency mixer and is used for processing the signals, so that spurious signals are reduced, and the signals are relatively clean.
Description
Technical Field
The present application relates to the field of communications technologies, and in particular, to an up-converter and an up-conversion method.
Background
An up-converter is a device that shifts low frequency signals to high frequency bands in the frequency domain. For a transmitter, the up-converter has the advantages of simplifying the design and manufacturing difficulty of an antenna, facilitating the generation, improving the utilization rate of frequency spectrum, preventing same frequency interference and the like; for the signal generator, different high frequency signals can be generated using an up-converter.
A Digital to Analog Converter (DAC) is an important component of an up-Converter, which is a Converter that converts a discrete signal in the form of a binary number into an Analog signal based on a reference. The up-converter realizes the conversion of digital information and analog signals through the DAC. At present, most of the DACs in the up-converter are single-channel digital-to-analog converters. The frequency conversion architecture using a single-channel digital-to-analog converter commonly used in several projects includes a primary frequency conversion architecture and a secondary frequency conversion architecture. The primary frequency conversion framework carries out primary frequency conversion on the modulated intermediate frequency signal for outputting, and the primary frequency conversion framework has the characteristics of simple structure, convenience in debugging and the like. However, due to the influence of the combined frequency of the quadrature and the mirror, a band-pass filter needs to be added to the output terminal. To complete broadband output, a band-pass filter is required to be correspondingly added for the output of each channel/adjacent channels, namely, a plurality of paths of band-pass filters are required, so that the up-converter is complex in structure, large in size and high in cost. In the existing secondary frequency conversion architecture, a single-channel DAC generates a low-intermediate frequency signal, and the low-intermediate frequency signal is subjected to first-stage frequency mixing (in the first-stage frequency mixing process, leakage of a first local oscillator LO1 is unavoidable, and larger spurious signals are generated when the first local oscillator LO1 enters a second-stage frequency mixer), so that the frequency is shifted from the low-intermediate frequency to a second-intermediate frequency, and out-of-band frequency components are filtered by a band-pass filter. The second intermediate frequency is transferred to the required frequency through a second-stage mixer, and the combined frequency of the interference is filtered by a filter. Although the up-converter adopting the secondary frequency conversion framework can meet the requirements of small frequency stepping and broadband frequency output, the up-converter adopting the secondary frequency conversion framework still has the defects of large volume, complex circuit structure and high implementation cost due to more components, complex structures and large volumes of partial components.
In summary, one of the technical problems that needs to be urgently solved by those skilled in the art is: how to reduce the size, structural complexity and implementation cost of an up-converter.
Disclosure of Invention
The technical problem to be solved by the application is to provide an up-converter and an up-conversion method, so as to solve the problems of large volume, complex circuit structure and high implementation cost of the existing up-converter.
In order to solve the above problem, the present application discloses an up-converter, including: the two-way digital-to-analog converter is used for converting the input baseband signals into two paths of orthogonal low-intermediate frequency signals to be output; and the analog quadrature modulator is used for receiving the two paths of orthogonal low-intermediate-frequency signals, modulating the two paths of orthogonal low-intermediate-frequency signals into intermediate-frequency signals by using a local oscillator signal of a first local oscillator in the up-converter and outputting the intermediate-frequency signals.
Preferably, a digital controlled oscillator is arranged in the two-way digital-to-analog converter, the digital controlled oscillator is configured to generate a carrier signal of a low intermediate frequency, and the carrier signal of the low intermediate frequency is used to perform frequency adjustment on the baseband signal.
Preferably, a digital quadrature modulator is further disposed in the two-way digital-to-analog converter, and the digital quadrature modulator is configured to modulate the baseband signal into two-way quadrature low-intermediate-frequency signals by using the low-intermediate-frequency carrier signal generated by the digitally controlled oscillator.
Preferably, the digital quadrature modulator is configured to multiply an in-phase signal in the baseband signal and an in-phase signal in the carrier signal of the low intermediate frequency, and multiply a quadrature signal in the baseband signal and a quadrature signal in the carrier signal of the low intermediate frequency, respectively; and sending the two products to an adder for processing, outputting two digital orthogonal low-intermediate frequency signals, and sending the two digital orthogonal low-intermediate frequency signals to a digital-to-analog conversion module in the two digital-to-analog converter for conversion into the two analog orthogonal low-intermediate frequency signals.
Preferably, the up-converter further comprises: and the secondary frequency conversion module is used for up-converting the intermediate frequency signal into a stable radio frequency signal.
Preferably, the secondary frequency conversion module includes: the device comprises a band-pass filter, a mixer, a low-pass filter and an automatic level control circuit; the band-pass filter is used for performing band-pass filtering on the intermediate frequency signal; the mixer is used for adjusting the intermediate frequency signal subjected to band-pass filtering into a required radio frequency signal; the low-pass filter is used for performing low-pass filtering on the radio-frequency signal adjusted by the mixer; and the automatic level control circuit is used for performing stability adjustment on the radio-frequency signal subjected to the low-pass filtering and outputting a stable radio-frequency signal.
Preferably, the band pass filter is a dielectric filter.
Preferably, the frequency mixer is a frequency mixer in which the isolation between the second local oscillator to radio frequency port and the intermediate frequency port is greater than or equal to 35 decibels.
In order to solve the above problem, the present application further discloses an up-conversion method, including: converting an input baseband signal into two paths of orthogonal low-intermediate frequency signals by using a two-path digital-to-analog converter and outputting the two paths of orthogonal low-intermediate frequency signals; receiving the two paths of orthogonal low-intermediate frequency signals through an analog orthogonal modulator, and modulating the two paths of orthogonal low-intermediate frequency signals into intermediate frequency signals by using local oscillation signals of a first local oscillator; and adjusting the intermediate frequency signal into a required radio frequency signal and outputting the radio frequency signal.
Preferably, the step of converting the input baseband signal into two paths of orthogonal low-intermediate frequency signals by using a two-path digital-to-analog converter and outputting the two paths of orthogonal low-intermediate frequency signals includes: generating a carrier signal of a low intermediate frequency using a numerically controlled oscillator in the two-way digital-to-analog converter; using the carrier signal of the low intermediate frequency to adjust the frequency of the baseband signal to generate two paths of digital orthogonal low intermediate frequency signals; and converting the two paths of digital orthogonal low-intermediate frequency signals into analog two paths of orthogonal low-intermediate frequency signals and outputting the analog two paths of orthogonal low-intermediate frequency signals.
Preferably, the step of adjusting the frequency of the baseband signal by using the carrier signal of the low intermediate frequency to generate two digital orthogonal low intermediate frequency signals includes: multiplying an in-phase signal in the baseband signal and an in-phase signal in the carrier signal of the low intermediate frequency by using the digital quadrature modulator, respectively, and multiplying a quadrature signal in the baseband signal and a quadrature signal in the carrier signal of the low intermediate frequency by using the digital quadrature modulator; and sending the two products to an adder for processing, and outputting the two paths of digital orthogonal low-intermediate frequency signals.
Compared with the prior art, the method has the following advantages:
this application is through double-circuit digital analog converter, directly converts the low intermediate frequency signal of two routes quadrature with the baseband signal of input into, and then modulates this low intermediate frequency signal into intermediate frequency signal through simulation quadrature modulator, has realized the first up-conversion adjustment in the secondary frequency conversion. Compared with the prior art that a modulator and a DAC are used for realizing the conversion of the unmodulated baseband signal and the low intermediate frequency signal, the quadrature modulation function and the conversion function from the baseband signal to the low intermediate frequency signal are integrated in the two-way digital-to-analog converter without being respectively completed by a plurality of parts, so that the realization parts are reduced, and the volume, the circuit complexity and the realization cost of an up-converter are reduced; the baseband signals are converted into low and intermediate frequency signals after passing through the two-way digital-to-analog converter, and small-step power adjustment can be realized without using an additional frequency adjusting device, so that the implementation cost of the up-converter is further reduced, and the circuit complexity is simplified; compared with the prior art that the low intermediate frequency signal is adjusted to the intermediate frequency signal by using a mixer, the mixer is larger than the analog quadrature modulator in terms of volume, circuit structure complexity or implementation cost, so that the volume, circuit complexity and implementation cost of the up-converter are further reduced; and moreover, the analog quadrature modulator is used for replacing the mixer to process the signals, so that spurious signals are reduced, and the signals are cleaner.
Drawings
Fig. 1 is a block diagram of an up-converter according to a first embodiment of the present application;
fig. 2 is a block diagram of an up-converter according to a second embodiment of the present application;
fig. 3 is a schematic structural diagram of an up-converter according to a third embodiment of the present application;
fig. 4 is a flowchart illustrating steps of an up-conversion method according to a fourth embodiment of the present application.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, the present application is described in further detail with reference to the accompanying drawings and the detailed description.
Example one
Referring to fig. 1, a block diagram of an up-converter according to a first embodiment of the present application is shown.
The up-converter of the present embodiment includes a two-way digital-to-analog converter 102 and an analog quadrature modulator 104. The two-way digital-to-analog converter 102 is configured to convert an input baseband signal into two orthogonal low-intermediate frequency signals and output the two orthogonal low-intermediate frequency signals; and the analog quadrature modulator 104 is configured to receive the two paths of orthogonal low-intermediate frequency signals, modulate the two paths of orthogonal low-intermediate frequency signals into intermediate frequency signals using a local oscillator signal of a first local oscillator in the up-converter, and output the intermediate frequency signals.
As is well known to those skilled in the art, the low-IF frequency is generally 36-70 MHz and the intermediate frequency is generally 1166-1200 MHz relative to the intermediate frequency.
In this embodiment, the two-way digital-to-analog converter 102 receives two input baseband digital signals without quadrature modulation and converts the two input baseband digital signals into two orthogonal low-intermediate frequency signals, and the two-way digital-to-analog converter 102 may convert the input baseband digital signals into two orthogonal low-intermediate frequency signals in any suitable manner, for example, through a suitable module and/or circuit, or call other modules and/or circuits. Preferably, the baseband signal without quadrature modulation can be converted into two quadrature low intermediate frequency signals by arranging appropriate modules and/or circuits in the two-way digital-to-analog converter, for example, arranging a digital quadrature modulator and/or an NCO (numerically controlled oscillator) and the like. The quadrature signal is also called an IQ signal, and is a signal having an in-phase signal I (in-phase) and a quadrature signal q (quadrature) which are equal in amplitude and different in phase by 90 degrees.
It should be noted that, the two-way digital-to-analog converter 102 in this embodiment may also adopt two one-way digital-to-analog converters, and combine with a modulator and/or an NCO, etc., to implement conversion of an input baseband signal into two orthogonal low-intermediate frequency signals.
The local oscillator is referred to as a local oscillator, and a signal generated by the local oscillator is referred to as a local oscillation signal. In this embodiment, the analog orthogonal modulator 104 modulates the two paths of orthogonal low-if signals into an intermediate-frequency signal by using a local oscillation signal of a first local oscillator in the up-converter, and then outputs the intermediate-frequency signal. After the intermediate frequency signal is output, other elements in the up-converter can further adjust the intermediate frequency signal, and finally the up-converter is up-converted into radio frequency output meeting the requirement.
Through this embodiment, directly convert the baseband signal of input into the low intermediate frequency signal of two ways quadrature with two-way digital analog converter, and then modulate this low intermediate frequency signal into the intermediate frequency signal through simulating quadrature modulator, realized the first up-conversion adjustment in the secondary frequency conversion. Compared with the prior art that a modulator and a DAC are used for realizing the conversion of the unmodulated baseband signal and the low intermediate frequency signal, the quadrature modulation function and the conversion function from the baseband signal to the low intermediate frequency signal are integrated in the two-way digital-to-analog converter without being respectively completed by a plurality of parts, so that the realization parts are reduced, and the volume, the circuit complexity and the realization cost of an up-converter are reduced; the baseband signals are converted into low and intermediate frequency signals after passing through the two-way digital-to-analog converter, and small-step power adjustment can be realized without using an additional frequency adjusting device, so that the implementation cost of the up-converter is further reduced, and the circuit complexity is simplified; compared with the prior art that the low intermediate frequency signal is adjusted to the intermediate frequency signal by using a mixer, the mixer is larger than the analog quadrature modulator in terms of volume, circuit structure complexity or implementation cost, so that the volume, circuit complexity and implementation cost of the up-converter are further reduced; and, use the analog quadrature modulator to replace the mixer, reduced the spurious signal, make the signal cleaner.
Example two
Referring to fig. 2, a block diagram of an up-converter according to a second embodiment of the present application is shown.
The up-converter of the present embodiment includes: a two-way digital-to-analog converter 202, configured to convert an input baseband signal into two orthogonal low-intermediate frequency signals and output the two orthogonal low-intermediate frequency signals; the analog quadrature modulator 204 is configured to receive the two paths of orthogonal low-intermediate frequency signals, modulate the two paths of orthogonal low-intermediate frequency signals into intermediate frequency signals using a local oscillator signal of a first local oscillator in the up-converter, and output the intermediate frequency signals.
The two-way digital-to-analog converter 202 is provided with a digital controlled oscillator 2022 and a digital quadrature modulator 2024. The digitally controlled oscillator 2022 is configured to generate a carrier signal with a low intermediate frequency, which is used to perform frequency adjustment on the baseband signal; the digital quadrature modulator 2024 is configured to modulate the baseband signal into two paths of quadrature low intermediate frequency signals by using the low intermediate frequency carrier signal generated by the digitally controlled oscillator 2022.
Among them, a Numerically Controlled Oscillator (NCO) is a digital function generator, typically a digital sine waveform generator, that generates synchronous, discrete-time, discrete values. The principle is that a frequency control word register sends a received frequency control word to a phase accumulator, the phase accumulator counts a system clock, the phase is accumulated when the value of the input frequency control word is reached, then the accumulated value is sent to a phase adder and is added with an initial phase received by the phase control word register to obtain a current phase value, and a cycle is completed. NCO is also an important component of software radio. A digital Quadrature modulator (QAM) is a device that amplitude-modulates two carrier waves having the same frequency and orthogonal phases with two modulation signals, and then combines the modulated signals together by an adder to send out the modulated signals. The embodiment fully utilizes the above performances of NCO and QAM to convert baseband signals without quadrature modulation into two paths of quadrature low-intermediate frequency signals.
By arranging the digitally controlled oscillator 2022 in the two-way digital-to-analog converter 202, the small step frequency adjustment of the baseband signal can be realized without depending on an external mixer, so that compared with the implementation mode of the external mixer, the frequency adjustment cost is saved, and the volume and the circuit complexity of the frequency adjustment implementation device are reduced. By arranging the digital quadrature modulator 2024 in the dual-path digital-to-analog converter 202, modulation from a baseband signal to two paths of quadrature low-intermediate frequency signals can be realized inside the dual-path digital-to-analog converter 202, which not only improves the integration level of the up-converter, but also further reduces the cost, volume and circuit complexity of the step adjustment realizing device.
After the two-way digital-to-analog converter 202 realizes the small step frequency adjustment of the baseband signal, when the up-converter subsequently performs the large step frequency adjustment on the baseband signal, a mixer with better cost performance can be selected for processing, and an expensive mixer is not needed.
In general, small step frequency adjustment means frequency adjustment in 1Hz steps, and large step frequency adjustment means frequency adjustment in 1MHz steps. In this embodiment, to meet the requirements of the wireless digital multimedia broadcasting system, the frequency adjustment of 1Hz is adopted for the small step frequency adjustment.
Preferably, the digital quadrature modulator 2024 is configured to multiply the in-phase signal in the baseband signal and the in-phase signal in the carrier signal of the low intermediate frequency, and multiply the quadrature signal in the baseband signal and the quadrature signal in the carrier signal of the low intermediate frequency, respectively; then, the two products are sent to an adder for performing corresponding addition processing, so as to generate two digital orthogonal low-intermediate frequency signals, and send the two digital orthogonal low-intermediate frequency signals to a corresponding digital-to-analog conversion module (not shown in the figure) in the two-way digital-to-analog converter 202 for conversion into two analog orthogonal low-intermediate frequency signals.
After the analog quadrature modulator 204 modulates the output intermediate frequency signal, other functional elements in the up-converter further perform corresponding processing on the intermediate frequency signal, and finally output a radio frequency signal meeting the requirement. For example, a secondary frequency conversion module disposed in the up-converter further up-converts the intermediate frequency signal into a stable radio frequency signal.
Preferably, the secondary frequency conversion module includes: the device comprises a band-pass filter, a mixer, a low-pass filter and an automatic level control circuit; the band-pass filter is used for performing band-pass filtering on the intermediate frequency signal; a mixer for adjusting the intermediate frequency signal subjected to band-pass filtering to a required radio frequency signal; the low-pass filter is used for performing low-pass filtering on the radio-frequency signal adjusted by the frequency mixer; and the automatic level control circuit is used for performing stability adjustment on the radio-frequency signal subjected to the low-pass filtering and outputting a stable radio-frequency signal. But not limited thereto, it should be clear to those skilled in the art that any other suitable means may be adopted in the process of further up-converting the intermediate frequency signal into the radio frequency signal, and the application is not limited thereto.
In the embodiment, the numerically-controlled oscillator and/or the digital quadrature modulator are/is arranged in the two-way digital-to-analog converter, so that the integration level of the up-converter is improved, the volume of the up-converter is reduced, and the circuit structure complexity and the implementation cost of the up-converter are reduced.
EXAMPLE III
Referring to fig. 3, a schematic structural diagram of an up-converter according to a third embodiment of the present application is shown.
The up-converter of the present embodiment includes: a two-way digital-to-analog converter DAC, an analog quadrature modulator, a band pass filter, a Mixer (Mixer), a low pass filter, an automatic level control circuit (ALC), a first local oscillator (LO1), and a second local oscillator (LO 2).
The two-way digital-to-analog converter of the embodiment can adjust the phase and amplitude of the two signals output by the two-way digital-to-analog converter, so that the phases of the two analog signals can be adjustedThe potential difference is 90 degrees, and the homography quadrature modulator has good inhibition effect on sideband and carrier leakage of the output signal after the first up-conversion. The two-way digital-to-analog converter is provided with a 32-bit Numerically Controlled Oscillator (NCO) and a digital quadrature modulator, and the frequency generated by the NCO in actual work is fIFThe carrier signal to a digital quadrature modulator, and the digital quadrature modulator combines an in-phase signal (in-phase) and a quadrature signal (quadrature) from the baseband with a frequency fIFThe in-phase and quadrature components of the carrier signal are multiplied first, the products of the two paths enter an adder to be added, and IQ two paths of low intermediate frequency f are outputIF_iAnd iIF_q，fIF_iAnd fIF_qAfter anti-aliasing filtering by an anti-aliasing filter (connected to a two-way digital-to-analog converter and an analog quadrature modulator, not shown in the figure), the analog quadrature modulator is reached.
In the above process, fIF_iAnd fIF_qThe mathematical representation after anti-aliasing filtering by the anti-aliasing filter is as follows:
fIF_i(t)＝cos(2πfNCOt+φ)+D
fIF_q(t)＝cos(2πfNCOt+π/2)
wherein f isIF_i(t) is the same phase low intermediate frequency, fNCOIs the carrier of a digital quadrature modulator, D is the carrier DC component, fIF_qAnd (t) is the quadrature low intermediate frequency.
fIF_iAnd fIF_qCan be 8M signal bandwidth (applied in broadcasting and television), then fIFThe frequency resolution of (a) is: f. ofIF reolution＝fS/232Wherein f isSIs the sampling clock frequency of the two-way DAC, if fSResolution can be up to 0.06H, 240MZ。
It should be noted that the NCO is not limited to 32 bits, and in practical use, a person skilled in the art can flexibly adjust the NCO according to practical needs, for example, set the NCO to 64 bits, and the like, which is not limited in this application.
After the anti-aliasing filtered signal arrives at the analog quadrature modulator, the mathematical relationship of the analog quadrature modulator is as follows:
fRF_mod(t)＝fIF_i(t)cos(2πfLOt)+fIF_q(t)cos(2πfLOt)
＝cos(2πfNCOt+φ)cos(2πfLOt)+D cos(2πfLOt)-cos(2πfNCOt+π/2)sin(2πfLOt)
fRF _ mod lower sideband(t)＝cos(2πfLOt-2πfNCOt-φ)
fRF _ mod upper sideband(t)＝sin(2πfLOt+2πfNCOt)
Wherein f isIF_i(t) is the same phase low intermediate frequency, fNCOIs the carrier of a digital quadrature modulator, D is the carrier DC component, fIF_q(t) is a quadrature low intermediate frequency, fRF_mod(t) is the modulated signal output by the analog quadrature modulator, fLOIs the local oscillator signal of LO1 and phi is the quadrature phase error of the IQ signal.
From the above relationship, the analog quadrature modulator output fLO-fIF、fLO (leakage)、fLO+fIFThe components of the spectrum are equalized. For quadrature signals with no phase difference and zero initial phase,
fRF _ mod lower sideband(t)＝cos(2πfLOt-2πfNCOt-φ)＝cos(2π/2)＝0，
fRF _ mod upper sideband(t)＝sin(2πfLOt+2πfNCOt)＝sin(π/2)＝1，
The method can be seen that the lower sideband is well restrained, meanwhile, the power of the local oscillation signal is low, the isolation degree from the local oscillation port to the modulation output port is high, and good carrier wave restraint is achieved.
Further, the band-pass filter filters fLO+fIFComposition of other components, frequency fLO+fIFThe spectrum is relatively clean when the frequency is called high and medium frequency. In addition, through the double-path digital-to-analog converter and the analog quadrature modulator, carrier and image frequency is effectively suppressed, and sidebands and f are reducedLO (leakage)(carrier leakage), the spurious that needs the filtering is little promptly, adopts miniaturized band pass filter such as dielectric filter etc. can the filtering, further reduces up-converter volume to, it is higher to use miniaturized band pass filter cost-performance ratio, and the cost is lower.
The second LO is then mixed with LO2 by a mixer, which selects the LO to the mixer with higher isolation at the rf and if ports. Preferably, the mixers select mixers having local oscillator to radio frequency and intermediate frequency port isolation greater than or equal to 35dB (decibel) to effectively avoid signal leakage.
The mixing generates a required second-order difference frequency, and in order to prevent spurious products (such as third-order spurious products and fifth-order spurious products) generated in the mixing process from falling into a frequency band, a high-order low-pass filter is required to be connected behind the frequency band. The signal enters the mixer to be output, and the frequency conversion loss at the moment is about-8 dB.
In addition, the insertion loss of the transmission line, the amplifier, the mixer and the like under different frequencies is different, and the frequency conversion loss of the frequency converter fluctuates by about 2dB in a broadband range caused by the superposition of several factors. The common method for overcoming the unevenness of the broadband variable frequency output is to use an ALC (automatic level control) circuit at the output end to ensure the stability of the output power.
Through the embodiment, the up-converter with low cost and simple structure is provided, and the defects of complex adjustment, complex structure and the like of small step frequency in the prior art are overcome. The dual-path digital-to-analog converter with small step frequency adjustment and modulation functions is used, and the quadrature modulator is adopted to replace a first-stage mixer in an up-converter of the existing secondary frequency conversion architecture, so that the integration level of the up-converter is improved, the size, the structural complexity and the cost of the up-converter are reduced, the stray level of an output frequency spectrum is effectively reduced compared with the traditional frequency conversion scheme, the shoulder ratio of the output frequency spectrum is effectively improved, and the modulation error rate of a system is improved.
Example four
Referring to fig. 4, a flowchart illustrating steps of an up-conversion method according to the fourth embodiment of the present application is shown.
The up-conversion method of the embodiment comprises the following steps:
step S402: and converting the input baseband signal into two paths of orthogonal low-intermediate frequency signals by using a two-path digital-to-analog converter and outputting the two paths of orthogonal low-intermediate frequency signals.
The two-way digital-to-analog converter in this embodiment has the functions of quadrature modulation and small step frequency adjustment, and through the two-way digital-to-analog converter, an input baseband signal that is not quadrature-modulated is converted into two-way quadrature low-intermediate frequency signals. Preferably, the functions of small step frequency adjustment and quadrature modulation can be realized by arranging an NCO and a digital quadrature modulator in a two-way digital-to-analog converter.
Preferably, in the case that the NCO and the digital quadrature modulator are arranged in the two-way digital-to-analog converter, the numerically controlled oscillator in the two-way digital-to-analog converter in the up-converter may be used to generate the carrier signal with a low intermediate frequency; utilizing a digital quadrature modulator to adjust the frequency of a baseband signal by using a carrier signal of low intermediate frequency to generate two paths of digital orthogonal low intermediate frequency signals; and then the two paths of digital-to-analog converters convert the two paths of digital orthogonal low-intermediate frequency signals into two paths of analog orthogonal low-intermediate frequency signals and output the two paths of analog orthogonal low-intermediate frequency signals.
Preferably, when the digital quadrature modulator of the up-converter is used to perform frequency adjustment on the baseband signal by using the carrier signal of the low intermediate frequency to generate two digital paths of orthogonal low intermediate frequency signals, the digital quadrature modulator multiplies the in-phase signal in the baseband signal by the in-phase signal in the carrier signal of the low intermediate frequency, and multiplies the orthogonal signal in the baseband signal by the orthogonal signal in the carrier signal of the low intermediate frequency; then, after the two products are sent to an adder for processing, two paths of orthogonal digital low-intermediate frequency signals are output.
Step S404: and receiving the two paths of orthogonal low-intermediate frequency signals through the analog orthogonal modulator, and modulating the two paths of orthogonal low-intermediate frequency signals into intermediate frequency signals by using local oscillation signals of a first local oscillator.
In this embodiment, the first local oscillator is connected to the analog quadrature modulator, and sends the generated local oscillator signal to the analog quadrature modulator, and the analog quadrature modulator modulates the local oscillator signal of the first local oscillator and the two paths of orthogonal low intermediate frequency signals into an intermediate frequency signal.
Step S406: and adjusting the intermediate frequency signal into a required radio frequency signal and outputting the radio frequency signal.
In the up-converter, the component for adjusting the intermediate frequency signal to the required radio frequency signal and outputting the same can be realized by a corresponding secondary frequency conversion component in the up-converter, such as a band-pass filter, a mixer, a low-pass filter, etc. In contrast, when a band pass filter is used, a miniaturized band pass filter (such as a dielectric filter) may be used to perform band pass filtering on the intermediate frequency signal. In addition, when the mixer is selected, a mixer with the isolation between the local oscillator and the radio frequency port and the isolation between the local oscillator and the radio frequency port being greater than or equal to 35 decibels can be selected, and the intermediate frequency signal subjected to band-pass filtering is adjusted to be the required radio frequency signal.
The up-conversion method of this embodiment can be implemented by using the corresponding up-converters in the foregoing multiple apparatus embodiments, and has the beneficial effects of the foregoing multiple corresponding apparatus embodiments, which are not described herein again.
By the present application, an up-converter in the field of wireless communication technology is provided, which may be used, in particular, as an up-conversion unit in a wireless digital multimedia broadcasting system. The up-converter combines respective advantages in the modulator scheme and the traditional mixing scheme, the modulator has the functions of sideband and carrier suppression, and the passive mixer has the characteristic of low noise, improves the stray level of an output frequency spectrum, avoids the dependence of direct frequency conversion on a small step local oscillator by using the small step of the intermediate frequency, and reduces the cost, the volume and the circuit complexity of the up-converter.
The embodiments in the present specification are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the method embodiment, the description is simple, and the relevant points can be referred to the partial description of the device embodiment.
The above describes an up-converter and an up-conversion method provided by the present application in detail, and a specific example is applied in the present application to explain the principle and the implementation of the present application, and the description of the above embodiment is only used to help understand the method and the core idea of the present application; meanwhile, for a person skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.
Claims (11)
1. An up-converter, comprising:
the two-way digital-to-analog converter is used for converting the input baseband signals into two paths of orthogonal low-intermediate frequency signals to be output;
and the analog quadrature modulator is used for receiving the two paths of orthogonal low-intermediate-frequency signals, modulating the two paths of orthogonal low-intermediate-frequency signals into intermediate-frequency signals by using a local oscillator signal of a first local oscillator in the up-converter and outputting the intermediate-frequency signals.
2. The up-converter according to claim 1, wherein a digital controlled oscillator is provided in the two-way digital-to-analog converter, the digital controlled oscillator is configured to generate a carrier signal with a low intermediate frequency, and the carrier signal with the low intermediate frequency is configured to perform frequency adjustment on the baseband signal.
3. The up-converter according to claim 2, wherein a digital quadrature modulator is further disposed in the two-way digital-to-analog converter, and the digital quadrature modulator is configured to modulate the baseband signal into two-way quadrature low intermediate frequency signals by using the low intermediate frequency carrier signal generated by the digitally controlled oscillator.
4. The up-converter according to claim 3, wherein the digital quadrature modulator is configured to multiply an in-phase signal of the baseband signal and an in-phase signal of the carrier signal of the low intermediate frequency, and to multiply a quadrature signal of the baseband signal and a quadrature signal of the carrier signal of the low intermediate frequency, respectively; and sending the two products to an adder for processing, outputting two digital orthogonal low-intermediate frequency signals, and sending the two digital orthogonal low-intermediate frequency signals to a digital-to-analog conversion module in the two digital-to-analog converter for conversion into the two analog orthogonal low-intermediate frequency signals.
5. The upconverter of claim 1, further comprising: and the secondary frequency conversion module is used for up-converting the intermediate frequency signal into a stable radio frequency signal.
6. The upconverter of claim 5, wherein the secondary frequency conversion module comprises: the device comprises a band-pass filter, a mixer, a low-pass filter and an automatic level control circuit;
wherein,
the band-pass filter is used for performing band-pass filtering on the intermediate frequency signal;
the mixer is used for adjusting the intermediate frequency signal subjected to band-pass filtering into a required radio frequency signal;
the low-pass filter is used for performing low-pass filtering on the radio-frequency signal adjusted by the mixer;
and the automatic level control circuit is used for performing stability adjustment on the radio-frequency signal subjected to the low-pass filtering and outputting a stable radio-frequency signal.
7. Upconverter according to claim 6, characterized in that the band pass filter is a dielectric filter.
8. The upconverter of claim 6, wherein the mixer is a second local oscillator to radio frequency port and intermediate frequency port isolation greater than or equal to 35 decibels.
9. An up-conversion method, comprising:
converting an input baseband signal into two paths of orthogonal low-intermediate frequency signals by using a two-path digital-to-analog converter and outputting the two paths of orthogonal low-intermediate frequency signals;
receiving the two paths of orthogonal low-intermediate frequency signals through an analog orthogonal modulator, and modulating the two paths of orthogonal low-intermediate frequency signals into intermediate frequency signals by using local oscillation signals of a first local oscillator;
and adjusting the intermediate frequency signal into a required radio frequency signal and outputting the radio frequency signal.
10. The method of claim 9, wherein the step of converting the input baseband signal into two paths of quadrature low intermediate frequency signals using a two-path digital-to-analog converter and outputting the two paths of quadrature low intermediate frequency signals comprises:
generating a carrier signal of a low intermediate frequency using a numerically controlled oscillator in the two-way digital-to-analog converter;
using the carrier signal of the low intermediate frequency to adjust the frequency of the baseband signal to generate two paths of digital orthogonal low intermediate frequency signals;
and converting the two paths of digital orthogonal low-intermediate frequency signals into analog two paths of orthogonal low-intermediate frequency signals and outputting the analog two paths of orthogonal low-intermediate frequency signals.
11. The method of claim 10, wherein the step of using the carrier signal of the low intermediate frequency to frequency adjust the baseband signal to generate the digital two-way quadrature low intermediate frequency signal comprises:
multiplying an in-phase signal in the baseband signal and an in-phase signal in the carrier signal of the low intermediate frequency by using the digital quadrature modulator, respectively, and multiplying a quadrature signal in the baseband signal and a quadrature signal in the carrier signal of the low intermediate frequency by using the digital quadrature modulator;
and sending the two products to an adder for processing, and outputting the two paths of digital orthogonal low-intermediate frequency signals.
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Application publication date: 20120815 |