Abstract:
A digital radio frequency receiver capable of receiving RF signals at a plurality of signal strengths thereby extending the dynamic range of the receiver without introducing a control loop while allowing a stable gain control algorithm to be implemented in software is described. Various embodiments of a digital radio receiver process a range of signals outside normal analog to digital converter capabilities and bypass the delays resulting from gain control loops.

Description:
BACKGROUND 
   Radio systems are intended to handle a wide range of signal strengths. In a digital radio system the analog to digital converter (“ADC”) places a constraint on the range of signals that may be handled. The range of signals that can be reliably transmitted in a device is described as the dynamic range. Digitizing electronics are often carefully designed so the dynamic range encompasses the range of information signals utilized by the device. Thus an ADC trying to record, with acceptable resolution, light pulses from low magnitude signals such as minimum ionizing tracks and from higher magnitude signals such as energetic showers in a calorimeter, will necessarily need a large information range (usually given as a word length, e.g. 10 or more bits). The dynamic range is sometimes expressed as the ratio between the highest and lowest signal and may be measured in decibels (i.e. the logarithmic expression of this ratio). 
   In prior art methods, the effective range of an ADC may be extended by using a non-linear response. This approach extends the dynamic range, preserving all relevant information; however, some processing is required so that the information is translated back to a linear scale. For a non-linear response, the error given by the least count (i.e. the smallest step by which digitized signals can be different) does not translate into a constant absolute error, resulting in different degrees of resolution dependent upon signal strength. 
   A prior art digital radio system uses two gain stages to extend the dynamic range of the ADC. This prior art system takes samples only during hopping where a hop&#39;s worth of samples are accumulated for each stream and a choice of which stream to use is then determined at the end of a hop. In this prior art system the samples are taken at different times for each stage. Consequently, the streams cannot be combined. 
   Other prior art approaches to extend the dynamic range of an ADC employ automatic gain control (AGC) loops. Prior art radios employing this method are designed to implement a plurality of communication techniques each of which imposes unique requirements on the AGC used. In the prior art, attempts have been made to implement AGC algorithms in software so that each waveform might have a unique algorithm customized to its particular needs. However, the software generally introduces delays into the control loop making it nearly impossible to implement stable and effective gain control loops. 
   In view of the present need and the deficiencies of the prior art, it is an object of an embodiment of the present invention to provide a novel method and system to extend the dynamic range of a digital system without introducing a control loop and to allow a quasi, non-causal and stable gain control algorithm to be implemented in software. 
   It is also an object of an embodiment of the present invention to provide a radio receiver to handle a range of signals that is outside the capabilities of current analog to digital converters. 
   It is another object of an embodiment of the present invention to provide a radio frequency receiver for receiving a plurality of signal strengths wherein said radio receiver contains a plurality of gain streams, an ADC, a controller and a digital signal processor. Furthermore, said gain streams contain an amplifier applying a different incremental gain to the communication signal. 
   It is yet another object of an embodiment of the present invention to provide an improvement of an apparatus for converting an analog signal to a digital signal where the apparatus includes a quantifier with a fixed dynamic range, a DSP and at least two fixed gain amplifying parallel branches. Wherein, each said fixed gain amplifying branches amplify the analog signal. The improvement comprises using gain amplifiers that have different gains in the parallel branches. 
   It is still another object of an embodiment of the present invention to provide a method to extend the dynamic range of a radio receiver without a gain control loop. The method includes the steps of obtaining a communication signal, amplifying the signal at different gains and converting the signal to digital data. 
   It is still yet another object of an embodiment of the present invention to provide a novel signal processing apparatus for recovering information from an analog input signal and producing a digital output signal representative of said information. The apparatus including comprising plural parallel circuits each adapted to receive said analog input signal and produce therefrom a quantized signal which is amplified by an amount different than the other said parallel circuits. The apparatus also including a logic circuit for receiving the quantized signals from the parallel circuits and recovering said information from the quantized signals to thereby produce a digital output signal representative of said information. 
   It is an additional object of an embodiment of the present invention to provide a novel improvement to a signal processing apparatus for recovering information from an analog input signal and producing a digital output signal representative of said information including a signal processing circuit including a quantizer with a fixed dynamic range. The improvement including plural parallel circuits replacing said signal processing circuit wherein said plural parallel circuits are each-adapted to receive said analog input signal and produce therefrom a quantized signal which is amplified by an amount different than the other said parallel circuits. The improve signal processing apparatus also including a logic circuit for receiving the quantized signals from the parallel circuits and recovering said information from the quantized signals to thereby produce a digital output signal representative of said information. 
   It is still an additional object of an embodiment of the present invention to provide a novel improvement for a signal processing apparatus for recovering information from an analog input signal and producing a digital output signal representative of said information, wherein said apparatus comprises a signal processing circuit including a quantizer with a fixed dynamic range and an AGC loop. The improved signal processing apparatus including plural parallel circuits replacing said signal processing circuit wherein said plural parallel circuits are each adapted to receive said analog input signal and produce therefrom a quantized signal which is amplified by an amount different than the other said parallel circuits. The improved signal processing apparatus also including a logic circuit for receiving the quantized signals from the parallel circuits and recovering said information from the quantized signals to thereby produce a digital output signal representative of said information. 
   These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a functional diagram of a receiver according to an embodiment of the present invention. 
       FIG. 2  is a functional diagram of a receiver with a multiplexer according to an embodiment of the present invention. 
       FIG. 3  is a functional diagram of a receiver with a single sample and hold circuit according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Embodiments of the present invention enable multiple synchronized streams of digital data sampled at different gain levels various gains to be available to the digital signal processor (DSP). The DSP may utilize the multiple streams in various processes. The DSP may choose one stream from the choices or perform a weighted sum of streams to produce a greater resolution. The methods selected may necessarily be unique to the particular waveforms and may be implemented by software algorithms. Since all the sample streams are supplied to the DSP, no control loop is needed to maintain the signal within the dynamic range of the ADC. An indicator of whether or not the amplified signal of a gain stream is outside the dynamic range of the ADC may be advantageously included in the sample stream. The implementation of the invention therefore provides an instantaneous dynamic range that is limited only by the number of gain streams the designer chooses to support. 
   An embodiment of the invention is shown in  FIG. 1 . The receiver  100  comprises radio hardware  110  including circuitry commonly used such as oscillators and filters. The radio hardware shown in  FIG. 1  also includes an antennae  111 ; however, the communication signals may be equally obtained by a hard wired connection such as a cable or similar means. The obtained communication signal is in the form of an analog signal. The signal is supplied to a plurality of parallel gain streams  120 . Each of the parallel gain streams  120  in the embodiment of  FIG. 1  contains an amplifier  122  and an ADC  121 . The amplifiers provide a fixed gain to the communication signal that is different in each gain stream. The gain function for the gain stream n(i) is nominally described as G+(i−1)x, where G is a constant, x is a predetermined amount of gain, and n(i) is the i th  gain stream from the group of N gain streams. The embodiment in  FIG. 1  shows 4 gain streams; however, any number of gain streams may be implemented in embodiments of the present invention. 
   The amplified communication signals in each of the branches (streams) are synchronously converted in each stream by the ADC  121 , resulting in N synchronized digital signals streams representing the analog communication signal at N different gains. These digital signals are supplied to a controller  130  which contains memory and control logic. The controller provides the synchronized digital signals to the DSP  140 . 
   The implementation may be affected by embodiments utilizing a single ADC, multiple sample and hold circuits and a multiplexer (demultiplexer) to provide the plurality of streams to the controller  130 , granted that the product of the signal streams sample rate and the number of gain streams is smaller or equal to the maximum sample rate of the ADC. This embodiment is shown in  FIG. 2 . 
   The parallel gain streams in an embodiment shown in  FIG. 2  contain amplifiers  122  and sample and hold (S/H) circuits  223 . The amplified communication signals supplied by the amplifiers  122  are sampled by the S/H circuits  223  and the sampled amplitude is supplied to an input gate  251  of a demultiplexer  250  until the next sample is taken. The sample rate of the S/H circuit is at least equal to the symbol rate of the communication signal. The demultiplexer sequentially connects each of the parallel gain streams  220  to the ADC  221  at least once per sample. The ADC converts each sample communication signal into a corresponding digital signal for processing in the controller  130 . The sample rate of the ADC is at least equal to the product of the symbol rate and the number of parallel gain streams N. The operation of the demultiplexer is controlled by the controller  130  via connection  131 . The memory of the controller  130  contains N digital signals for each increment sampled by the S/H circuits  223 . The stored digital signals in the controller  130  are thus available for use in the DSP  140 . Thus the entire communication signal is available in digital form at N different gains. 
   Similarly, a single sample and hold circuit may precede the gain stages as shown in  FIG. 3 , if the dynamic range of the sample and hold circuit does not limit performance. An embodiment shown in  FIG. 3  includes parallel gain streams  320  containing only amplifiers  122 . A S/H circuit  323  samples the communication signal and provides the sample to each of the parallel gain streams  320 . The gain streams amplify the sample in the same manner as described above. A demultiplexer  250  sequentially connects each of the gain streams to the ADC  221  for digital conversion. Again in this embodiment the sample rate of the ADC  221  must be equal or greater than the product of the symbol rate and the number of gain streams N. 
   The controller  130  in embodiments of the invention determines which, if any, of the gain stream signals are outside of the dynamic range of the ADC  221 . The digital signals resulting from those gain streams outside of the dynamic range are designated so as to be differentiated from the gain streams that are within the dynamic range. The digital data associated with a gain stream outside of the dynamic range may then be discarded or weighted by the controller  130  and DSP  140  in order to facilitate accurate information recovery from the digital signals. 
   The control logic of the controller  130  and the processing of the DSP  140  may be advantageously established through software algorithms applicable to various signal communication techniques capable of being received by the receiver  100 . 
   While preferred embodiments of the present invention have been described, it is to be understood that the embodiments described are illustrative only and that the scope of the invention is to be defined solely by the appended claims when accorded a full range of equivalence, many variations and modifications naturally occurring to those of skill in the art from a perusal hereof.