CN1463501A - 接收器中中频信号的正交包络采样 - Google Patents

接收器中中频信号的正交包络采样 Download PDF

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CN1463501A
CN1463501A CN02801836A CN02801836A CN1463501A CN 1463501 A CN1463501 A CN 1463501A CN 02801836 A CN02801836 A CN 02801836A CN 02801836 A CN02801836 A CN 02801836A CN 1463501 A CN1463501 A CN 1463501A
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Y·范
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Koninklijke Philips NV
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    • H04B1/0007—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage
    • H04B1/0014—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage using DSP [Digital Signal Processor] quadrature modulation and demodulation
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    • H—ELECTRICITY
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    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
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    • H04B1/0007—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage
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    • H04L27/3845—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier
    • H04L27/3881—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier using sampling and digital processing, not including digital systems which imitate heterodyne or homodyne demodulation
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Abstract

一种用于对接收到的信号进行二维直接中频采样的装置和方法。接收器配备有用于将接收到的射频信号转换成中频信号的电路。转换后的中频信号利用一对低通模数转换器进行采样。该采样方案包括中频信号的正交包络采样。该采样方案还包括在I通道信号采样后的1/4中频载波周期处对Q通道信号进行采样。

Description

接收器中中频信号的正交包络采样
本发明涉及接收器中中频信号的采样，更具体而言，涉及接收器中中频信号的正交包络采样。
无线设备，如码分多路访问(CDMA)或时分多路访问(TDMA)设备，中通过接收器的模拟信号采样是以几种方式执行的。在接收器中，射频(RF)信号转换成中频(IF)信号。一般使用一个IF级。在对射频(RF)和IF进行适当的放大和滤波后，接收到的信号由IF混频器转换成同相正交(I/Q)基带信号。该I/Q信号由一对低通通道滤波器进行滤波。同时，该I/Q低通滤波器的输出由一对低通模数转换器(ADC)进行采样。由该转换器产生的数字化数据由数字信号硬件处理来恢复期望的信息，如语音、图象及其它数据。由于I/Q IF混频器和I/Q低通滤波器的电路不匹配，I通道和Q通道之间的增益和相位频率响应经常是不相同的。这称为I/Q不平衡。此外，对于这种方法，DC补偿问题是常见的。
IF信号的带通采样是另一种采样方案。在这种方案中，接收到的信号由一个带通采样ADC在IF级直接进行采样。这种采样可以与重复采样或二次采样一起发生。与前面描述的传统I/Q低通采样方案相比，这种方案去掉了两个IF混频器和模拟低通滤波器。此外，该带通采样方案还消除了I/Q不平衡和DC补偿。但是，设计、制造和实现带通ADC与带通数字滤波器的成本和复杂程度及相关的功耗都有可能限制这种采样方法的使用。
所需要的是一种对接收到的信号进行采样的装置和方法，它不仅拥有先前设计的优点，而且还消除了与这种先前设计相关的额外成本和复杂程度。
本发明提供了一种用于对接收到的信号进行直接中频(IF)采样的装置和方法，其中接收到的信号由二维信号组，如正交相移键控(QPSK)和正交幅度调制(QAM)，进行调制。IF信号是由一对低通模数转换器进行采样的，从而与先前设计在维持同等性能时的更复杂更昂贵的带通模数转换器与数字带通滤波器相比，实现了功耗及制造成本的显著节约。
在其一种形式中，本发明包括克服了现有技术缺点的接收器。该接收器包括一个射频(RF)混频器、一个IF滤波器和一个放大器。直接连接到该放大器的是能够利用正交包络采样方案直接对IF信号进行采样的第一和第二ADC。此外，一个数字信号处理器(DSP)连接到第一和第二低通模数转换器，而且可以处理采样数据以恢复期望的信息。
此外，本发明还包括一种对接收器中由二维信号组进行调制的信号进行直接IF采样的方法。该方法包括接收信号和利用RF混频器将该信号转换到中频的步骤。该方法还包括对结果IF信号的滤波和放大。放大的IF信号由一对低通模数转换器利用正交包络采样方案直接进行采样。然后，利用DSP处理由低通模数转换器提取的采样信息以恢复期望的信息。
与先前采样方案相比，本发明的一个好处是降低的功耗，同时维持良好结果。
与先前采样方案相比，本发明的另一个好处是降低的复杂程度，同时维持良好结果。
本发明还有另一个好处是对数字信号的处理转移到天线。
参考以下描述的一种本发明实施方案并联系相应附图，本发明上述及其它特征和优点，及实现它们的方式将变得更加明显，而且本发明本身也将更好理解，其中：
图1是一种实现低通采样方案的现有技术超外差接收器结构。
图2是一种实现带通采样方案的现有技术超外差接收器结构。
图3是根据本发明实现正交包络采样方案的超外差接收器结构。
图4是根据本发明的正交包络采样方案的表示。
图5是通过正交包络采样的I通道基带信号的曲线图。
图6是通过正交包络采样的Q通道基带信号的曲线图。
图7是通过正交包络采样的Q通道信号畸变的曲线图。
图8是信号功率频谱及由正交包络采样方案产生的畸变的曲线图。
在多个视图中，对应的标号都指示对应的部件。在此列出的范例说明了本发明一种形式的优选实施方案，但这种范例不应当以任何方式认为是对本发明范围的限制。
现在参考附图，尤其是图1，示出了利用低通采样的现有技术超外差接收器体系结构。这个超外差接收器100使用低通采样。天线101接收输入的发射信号。天线101连接到双工器件102。双工器件102包括两个带通滤波器104和106。接收滤波器104可操作通过接收信号的频率。发射滤波器106可操作通过发射信号的频率。来自接收滤波器104的射频输出由低噪声放大器108接收。放大的输出由表面声波滤波器110接收。然后滤波后的信号发送到射频混频器112。射频混频器112利用射频混频器输入114将输入信号转换成中频信号。来自混频器112的IF输出输入到表面声波滤波器116。然后滤波后的信号输入到可变增益放大器118。连接到放大器118的是一对IF混频器120。IF混频器120将接收到的信号下变换成同相正交(I/Q)基带信号。然后该I/Q信号由一对低通通道滤波器126进行滤波。低通滤波器126的模拟输出由一对低通模数转换器128进行采样。转换器128的数字化输出输入到数字信号处理器130用于进一步处理以恢复期望的信息。低通模数转换器128可以是利用∑-Δ调制技术的转换器。
图2是利用带通采样的超外差接收器体系结构，总体上用200表示。天线201接收输入的发射信号。天线201连接到双工器件202。双工器件202包括两个带通滤波器204和206。接收滤波器204可操作通过接收信号的频率。发射滤波器206可操作通过发射信号的频率。来自接收滤波器204的射频输出由低噪声放大器208接收。放大的输出由表面声波滤波器210接收。然后滤波后的信号发送到射频混频器212。射频混频器212利用射频混频器输入214将输入信号转换成中频信号。来自混频器212的IF输出输入到表面声波滤波器216。然后滤波后的信号输入到可变增益放大器218。来自放大器218的IF放大输出输入到带通模数转换器220，该转换器对信号重复采样或二次采样。转换器220的输出由数字带通滤波器222滤波，然后发射，用于数字信号处理器224做进一步处理。
图3是根据本发明的接收器体系结构的优选实施方案。接收器300使用正交包络采样。天线301接收输入的发射信号。天线301连接到双工器件302。双工器件302包括两个滤波器304和306。接收滤波器304可操作通过接收信号的频率。发射滤波器306可操作通过发射信号的频率。来自接收滤波器304的射频输出由低噪声放大器308接收。放大的输出由表面声波滤波器310接收。然后滤波后的信号发送到射频混频器312。射频混频器312利用射频混频器输入314将输入信号转换成中频信号。来自混频器312的IF输出输入到表面声波滤波器316。然后滤波后的信号输入到可变增益放大器318。然后IF信号由一对低通模数转换器320直接进行采样。直接采样不包括放大器和模数转换器之间的任何干扰元件。由于不包括象现有技术中存在的在对IF信号采样之前的混频器和滤波器，因此直接采样允许不带任何混频器、模拟通道滤波器或类似干扰元件的IF信号采样。由于在接收器的设计和制造中引入较少部件，干扰元件的消除降低了成本和复杂程度。转换器320的输出输入到数字信号处理器322中用于进一步处理。利用这种体系结构的通道滤波由DSP执行，并且最小化了I/Q不平衡。通过利用低通模数转换器320的直接采样，在功耗和制造成本方面都可以实现显著的节约。这种配置公开了一种利用一对低通模数转换器320的用于I/Q信号对的直接IF正交包络采样方案。为了使正交包络采样方案能够正常工作，必须在低通模数转换器320的输入端给出一个快速采样保持电路。
在一种可选实施方案中，低通模数转换器320是∑-Δ模数转换器。在另一种可选实施方案中，低通模数转换器320是快速型ADC。如果低通模数转换器320是快速型转换器，则只需一个转换器，而不是一对转换器，从而进一步降低了成本和复杂程度。这是因为在正交包络采样中，I/Q通道不是像现有技术一样同时进行采样的。因此，通过时间复用，I通道和Q通道可以由一个ADC进行采样。
图4是根据本发明的创造性正交包络采样方案的图形表示。与传统的现有I/Q采样方案相比，根据正交包络采样方案的I/Q通道采样不在同一采样时间发生。在正交包络采样方案中，直接采样的IF信号由一种方案进行采样，在此方案中，在I通道ADC采样之前或者之后的1/4 IF载波周期处Q通道ADC进行采样。例如，在后面的1/4 IF载波周期处进行Q通道采样。I通道采样点通常在410处示出。Q通道采样点通常在420处，即I通道采样点410后90度示出。IF载波周期由TIF表示，而点410和点420之间的间距用由TIF/4表示的箭头示出。箭头之间的距离表示1/4 IF载波周期。采样频率与中频或者中频的次谐波频率相同。基本上，采样频率等于中频除以次谐波的次数(整数)。在图4a中，次谐波的次数为一(1)，它产生等于中频的采样频率。在图4b中，次谐波的次数为二(2)，它产生等于中频一半(1/2)的采样频率。由于中频一般远远大于信息带宽，因此在Q通道(或者I通道)中的采样延时(等于1/4 IF载波周期)不会产生如下所示的任何实际副作用。
图5提供了利用图4正交包络采样方案直接采样的I通道基带信号的图示曲线。图5包括两条曲线的图示，但是由于这两条曲线是相同的所以无法区分。一条曲线表示典型的I通道基带采样，另一条表示从IF信号进行正交包络采样的I通道。如所预期的，这两条I通道曲线是相同的。
图6提供了利用图4正交包络采样方案直接采样的Q通道基带信号的图示曲线。图6包括两条曲线的图示。一条曲线表示典型的Q通道基带采样，另一条表示从IF信号进行正交包络采样的Q通道。两条曲线之间的差别很小，因此曲线看起来相互重合。
图7提供了在与图6所使用相同周期上利用方程(6)对Q通道计算的畸变的曲线图。图7说明了为图6中两条曲线之间差异的畸变。由于中频远远高于信息带宽，所以畸变非常小。以下给出对正交包络采样方案的理论数字分析。
由S(t)表示的接收信号在方程(1)中表示，其幅值和相位由m(t)和θ(t)表示，带任意恒定的初始相位用θ。
     ＝m(t)·cos[ωIFt+(t)+θ]                                       (1)
S(t)
     ＝m(t)·cos[(t)+θ]·cos(ωIFt)-m(t)·sin[(t)+θ]·sin(ωIFt)当在此接收波形上对于I通道的采样点对准cos(ωIFt)的正峰值时(因为θ是任意的，所以可以做这样的假设)，即：
cos(ωIFt)＝1且sin(ωIFt)＝0，在第i个实例(t＝ti)中的I通道采样数据在方程(2)中给出。
I(ti)＝m(ti)·cos[(ti)+θ]                                                    (2)在第i个实例(t＝ti+δ，δ＝TIF/4，TIF是IF载波周期)的Q通道采样由方程(3)给出。
Q(ti)＝-m(ti+δ)·sin[(ti+δ)+θ]                                             (3)由于使用参考相位信息的DSP中的相位反转处理，如在CDMA蜂窝通信系统中，任意相位θ可以去掉。因此，有效的I/Q采样数据由方程(4)和(5)给出。
I(ti)＝m(ti)·cos[(ti)]                                                     (4)
Q(ti)＝-m(ti+δ)·sin[(ti+δ)]                                              (5)使用正交包络采样方案的Q通道采样数据发生畸变，在同图5和图6中信号相同周期上畸变的数量由方程(6)给出，并在图7中示出。
Δ(ti)＝m(ti)·sin[(ti)]-m(ti+δ)·sin[(ti+δ)]                          (6)
图8是信号功率频谱810和由方程(6)计算得到的畸变频谱820的图形曲线。在M个采样点上平均的期望信号能量和畸变信号能量之比(SDR)是利用方程(7)计算得到的。对CDMA通信系统在128芯片周期上计算得到的SDR大约为53dB。通过观察功率频谱810和畸变频谱820之间的差别，可以在图8中看到SDR值。 SDR = Σ i = 1 M [ Δ ( t i ) / m ( t i ) ] 2 / M - - - ( 7 )
非常高的SDR值从理论上预示正交包络采样方案不会有任何的副作用。
如图8所示，频谱分析显示畸变信号的频谱也是限带的，而且和图7中信号有相同的带宽。在频域中，正交包络采样方案使用数字采样的产生伪信号属性。因此，图象波段中的噪音会落入信号波段中。由于IF表面声波滤波器的过滤保护，大大降低了图象波段的噪音。因此，产生伪信号噪音效应不应当成为问题。当采样频率为中频的三次谐波时，例如IF＝183.6MHz，图象波段就已经在US蜂窝接收波段之外了。
尽管本发明描述为具有一种优选设计方案，但是在此公开内容的主旨和范围内，可以对本发明做进一步的修改。因此，该申请覆盖了本发明利用其基本原理的任何变化、使用或修改。此外，该申请还覆盖了与该说明书公开内容不同，但是在本发明所属技术领域中是已知的或常用实践范围内的，并在附权利要求限制范围内内容。

Claims (17)

1、一种接收器，包括：
射频混频器(312)；
中频滤波器(316)；
放大器(318)；其特征在于：
第一低通模数转换器(320)直接连接到所述放大器(318)；
第二低通模数转换器(320)直接连接到所述放大器(318)；及
数字信号处理器(322)连接到所述第一和第二低通模数转换器(320)。
2、根据权利要求1的接收器，其中所述接收器构成通信设备的一部分。
3、根据权利要求2的接收器，其中所述通信设备包括蜂窝电话。
4、根据权利要求2的接收器，其中所述通信设备包括无线设备。
5、根据权利要求2的接收器，其中所述通信设备包括码分多路访问(CDMA)设备。
6、根据权利要求2的接收器，其中所述通信设备包括时分多路访问(TDMA)设备。
7、根据权利要求1的接收器，还包括射频滤波器(310)。
8、根据权利要求7的接收器，其中所述射频滤波器包括一个表面声波滤波器(310)。
9、根据权利要求1的接收器，其中所述中频滤波器包括一个表面声波滤波器(316)。
10、根据权利要求1的接收器，其中所述放大器包括一个可变增益放大器(318)。
11、根据权利要求1的接收器，其中所述第一和第二低通模数转换器(320)包括∑-Δ模数转换器。
12、根据权利要求1的接收器，其中所述第一低通模数转换器(320)包括快速型模数转换器；
13、一种用于在接收器中直接对中频信号进行采样的方法，包括：
接收信号；
将所述信号转换成中频信号；
对所述中频信号滤波；
放大所述滤波后的中频信号；其特征在于
对所述放大的中频信号直接进行采样；及利用数字信号处理器(322)处理所述直接采样的信号。
14、根据权利要求13的方法，其中所述直接采样包括：
在预定时间对第一通道进行采样；及
在所述第一通道采样后的1/4中频载波周期处对第二通道进行采样。
15、根据权利要求13的方法，其中所述直接采样是由一对低通模数转换器(320)来完成的。
16、根据权利要求15的方法，其中所述低通模数转换器(320)包括∑-Δ模数转换器。
17、根据权利要求13的方法，其中所述直接采样是由一个快速型低通模数转换器来完成的。
CN02801836A 2001-05-25 2002-05-22 接收器中中频信号的正交包络采样 Pending CN1463501A (zh)

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