Abstract:
A variable responsivity adaptive detector system ( 10 ) for a receiver protects a baseband amplifier from being overdriven and used to detect weak signals at the antenna ( 14 ). The RF detector system ( 10 ) includes an envelope detector ( 28 ) configured to receive an RF signal, and a power detector ( 20 ) sensing a magnitude of the received RF signal and providing a DC signal for biasing the envelope detector ( 28 ) to modify the magnitude of the received RF signal.

Description:
FIELD 
       [0001]    The present invention generally relates to RF receivers and more particularly to a variable responsivity adaptive detector system within a receiver. 
       BACKGROUND 
       [0002]    The market for personal wireless electronic devices, for example, cell phones, personal digital assistants (PDA&#39;s), digital cameras, and music playback devices (MP3), is very competitive. Manufacturers are constantly improving their product with each model in an attempt to cut costs and production requirements. 
         [0003]    Global telecommunication systems, such as cell phones and two way radios, are migrating to higher frequencies and data rates due to increased consumer demand on usage and the desire for more content. Current mobile devices are challenged by the increased functionality and complexity of multi-modes, multi-bands, and multi-standards, and progressing beyond 3G with the increasing requirement of multimedia, mobile internet, connected home solutions, sensor-network, high-speed data connectivity such as Bluetooth, RFID, WLAN, WiMAX, UWB, and 4G. Limited battery power and tight design space will become bottlenecks for the high integration and development of mobile devices. The tight design space is especially challenging for RF technologies and the requisite design/fabrication of adaptive/tunable antennas and antenna arrays. 
         [0004]    Signals received at an antenna may encompass a wide range of power. Signals having a high magnitude of power may overdrive a baseband amplifier and signals having a low magnitude may be difficult to detect. Conventional automatic responsivity control circuits are known to decrease the magnitude of a high power received signal and to increase the magnitude of a low power received signal. These circuits typically include a variable gain amplifier coupled to the output and a differential amplifier for comparing the output with a reference source to produce a voltage controlling the gain of the variable gain amplifier. However, these conventional circuits require additional circuitry. 
         [0005]    U.S. Pat. No. 3,784,848 uses a varying amplitude of an oscillating signal generated from a touch receptor to change the detector sensitivity in a touch control circuit. 
         [0006]    U.S. Pat. No. 3,795,811 accomplishes automatic responsivity control by means of a reference signal derived from a modulated light source. The source illuminates both the infrared element array and a separate reference signal detector. The infrared video signal and the reference signal transmitted in each channel are passed through a variable gain amplifier. The magnitude (gain) of the reference signal is controlled by a circuit including a synchronous filter, a synchronous detector, a DC reference voltage circuit, and a voltage controlled resistor. A separate reference signal detector provides a drive signal to control the synchronous filter and also provide a 180 degree phase shifted reference signal that is used to cancel the reference signal in the output of the VGA. 
         [0007]    U.S. Pat. No. 4,276,474 provides automatic responsivity control for an array of infrared photodetectors. A modulated reference signal is provided by uniformly modulating the bias voltage applied to each of the plurality of photodetectors in the array. Photodetectors having different responsivities respond to the same bias modulation differently to produce a superimposed sinusoidal component in the photodectector output current which is used to compensate for differences in responsivities of the individual photodetectors. An autoresponsivity control circuit selects the superimposed sinusoidal component from the photodetector output current corresponding to the frequency of the reference signal modulating the bias voltage, and compares the amplitude of the selected sinusoidal component with a reference level to adjust the amplification at the photodetector output in accordance with this comparison, so that the amplified outputs from the plurality of photodetectors respond uniformly to the sinusoidal reference signal applied as a bias voltage to the photodetectors. 
         [0008]    Accordingly, it is desirable to provide a variable responsivity adaptive detector system for a receiver that can reduce dynamic range requirements for a baseband amplifier and can be implemented adaptively to self adjust for varying incident signal levels and frequencies. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Embodiments of the present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
           [0010]      FIG. 1  is a block diagram of a variable responsivity adaptive detector system in accordance with a first embodiment; 
           [0011]      FIG. 2  is a graph of responsivity versus bias for the first embodiment; 
           [0012]      FIG. 3  is a diagram of an exemplary RF detector voltage and desired RF envelope detector control voltage versus RF signal power. 
           [0013]      FIG. 4  is a diagram of a ASK modulated low power RF input signal; 
           [0014]      FIG. 5  is a diagram of a ASK modulated high power RF input signal; 
           [0015]      FIG. 6  is a diagram of an amplitude modulated wave form demodulated to a constant amplitude baseband differing RF signal amplitude using adaptive responsivity in accordance with the exemplary embodiments. 
           [0016]      FIG. 7  is a block diagram of a variable responsivity adaptive detector system in accordance with a second embodiment; and 
           [0017]      FIG. 8  is a graph of the gain versus frequency for different control voltage levels used to vary the gain in accordance with the second embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
         [0019]    An applied DC bias voltage adaptively controls the responsivity/sensitivity of an envelope detector within an RF receiver used to receive and demodulate amplitude modulated signals. Responsivity and sensitivity are used interchangeably to mean the ratio of wattage to voltage, or the input-output gain of a detector system. Received power at an antenna is coupled to a power detector which converts RF power into a DC voltage proportional to the received power at the antenna. Through a combination of detector diode selection, orientation, and buffer or differential amplification, this DC voltage can be applied to the envelope detector to vary the responsivity/sensitivity adaptively in relation to the received power at the antenna. Therefore, as power increases at the antenna, the responsivity of the detector decreases, or as power decreases at the antenna, the responsivity of the detector increases. The use of a DC bias voltage to control the responsivity of the envelop detector allows for improved dynamic range over conventional RF detector systems. This approach can also be implemented with systems using AGC (automatic gain control) to allow for even greater dynamic range. 
         [0020]    Referring to  FIG. 1 , a first embodiment includes the adaptive responsivity detector system  10  having an input conductor  12  configured, for example to be coupled to an antenna  14 , for providing a received signal to a coupler  16 . The received signal having a carrier frequency, for example in the range up to 3.0 THz, but preferably of approximately 60 GHz, is forwarded from the input conductor  12  to a low noise amplifier  18  in a conventional fashion. In accordance with the preferred exemplary embodiment, the received RF signal is envelope detected using RF envelope detector  28 . The RF envelope detector  28  comprises the bias tee circuit  26  coupled between a diode  36  and the low noise amplifier  18 . A load at the output of the envelope detector  28  is represented by a resistor  37 . This bias tee circuit  26  serves to isolate a DC input bias to the envelope detector diode  34  from the RF carrier frequency. A bias applied to RF envelope detector  28  may be used to control the responsivity of the detector. 
         [0021]    Coupler  16  may be implemented in any known fashion known, but preferably in a manner consistent with integration on a common substrate. This coupling factor, or relative signal sampled by the coupling, is preferably at least 10 dB reduced from the original signal to minimize impact on receiver sensitivity. The power detector  20 , comprising a diode  22  and load resistor  23  transforms power (RF signal from the coupler  16 ) into a DC voltage proportional to the received power at the antenna. This DC voltage can be converted by a differential amplifier  24  into a control signal that is applied to the detector  28  to vary the responsivity/sensitivity adaptively in relation to the received power at the antenna  14 . Therefore, as power increases at the antenna  14 , the responsivity of the envelope detector  28  decreases, or as power decreases at the antenna  14 , the responsivity of the envelope detector  28  increases. The use of a DC bias voltage to control the responsivity of the envelope detector  28  allows for improved dynamic range over conventional RF detector systems. 
         [0022]    Using a highly nonlinear diode as the diode  36 , for example, a Schottky diode or the Junction Engineered Dual Insulator (JEDI) technology developed at the University of Colorado as described in U.S. Pat. No. 6,563,185, allows for very high frequency detection. Through the use of this low cost, half-duplex JEDI technology, the integrated RF variable responsivity detector may be fabricated on non-semiconductor substrates such as FR-4 boards or any material including, for example, quartz, ceramics, Teflon, polyimides, plastic, liquid crystal polymer, and epoxy. Improved performance is accomplished by eliminating or reducing lossy interconnects, and positioning the demodulator in the vicinity of the antenna. 
         [0023]    The JEDI technology comprises nanoscale stacks of metals and insulators for creating ultra-high frequency diodes, antennas, and transistors operating at frequencies from DC to 3.0 THz. More specifically, a second layer of insulator and metal may be substituted for the semiconductor found in metal-oxide semiconductors, resulting in a four-layer stack of metal-insulator-insulator-metal (MIIM). A quantum well is formed between the insulators that allow only high-energy tunneling. Consequently, when a voltage is applied to the top metal that exceeds its threshold, a ballistic transport mechanism accelerates tunneling electrons across the insulator gap. In accordance with the exemplary embodiment, the diode  36  is chosen to have a nonlinear I/V characteristic which is resistive in nature. In other words, as an applied RF signal swings across the I/V characteristic of the diode, the effective resistance is changing in a time varying manner. 
         [0024]      FIG. 2  is a graph of responsivity versus bias voltage for a JEDI diode. As the amplitude of bias voltage increases, the responsivity (power/voltage) increases. In general, controlling the voltage of a detector diode can alter its responsivity characteristics, providing the opportunity to implement an adaptive responsivity RF receiver. 
         [0025]    The RF power detector  20  combined with amplifier  24  can be designed or configured by those skilled in the art to produce the appropriate control voltage necessary to control the RF envelope detector  28  in the desired manner. In this embodiment, the RF power detector may generate a positive DC voltage  23  which increases for higher RF signal strength to the antenna  14 . By loading the power detector  20  with a large DC load  19 , the responsivity of the power detector  20  can be optimized to detect the average carrier power. The inductor  21  coupled to ground is needed to provide a DC current return path for the rectified DC voltage  23  generated across the diode  22 . The inductor  21  prevents shorting out the RF signal. A high input impedance differential amplifier  24  can be used to level shift and invert the slope of the DC control signal  25  to the RF envelope detector  28 . Many other possible designs or configurations may be used to implement a similar function. Preferably, in this embodiment, a JEDI device, scaled for best average power detection would be used to allow higher levels of integration. 
         [0026]      FIGS. 4-6  show how an amplitude modulated signal is envelope detected in this adaptive responsivity receiver exemplary embodiment. By adapting the receiver responsivity or gain, the digital baseband signal can be constrained to smaller range of amplitudes for a given range of RF input signals, thereby reducing the baseband architecture dynamic range requirements.  FIG. 4  is a received RF signal  62  having a low power and  FIG. 5  is a received RF signal  64  having a high power. The exemplary embodiment will provide a signal  66  shown in  FIG. 6  in response to either of the RF signal  62  having a low power ( FIG. 4 ) or the RF signal  64  having a high power ( FIG. 5 ). 
         [0027]    Referring to  FIG. 7 , a second exemplary embodiment includes coupling the node  42  between the inverting amplifier  24  and the anode of the power detector diode  22  to a control gate  44  of the low noise amplifier  18 , thereby controlling the gain of a variable gain amplifier  18  in a similar fashion as the variable responsivity detector is controlled in the first embodiment. 
         [0028]      FIG. 8  is a graph showing the gain versus frequency for a typical RF amplifier. In this embodiment amplifier  18  may be gained controlled using a similar RF power detector approach used to control the responsivity of the RF envelope detector of  FIG. 1 . By modifying the differential amplifier  28  circuit the appropriate DC control voltage versus incident RF input power may be achieved. 
         [0029]    Both of these embodiments could be combined to achieve better overall dynamic range in the receiver. A combining of these two exemplary embodiments would provide a differentiated signal to both the gate  44  of the low noise amplifier  18  and the bias tee circuit  26 . Separate control signal circuits may be required for each. 
         [0030]    While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.