JP2009522837A - A receiver for broadband communication and a method for receiving data frames from a wireless device in a wireless local area network. - Google Patents

Abstract

The present invention relates to a broadband communication receiver (1), in particular a receiver in a wireless local area network, which receiver includes an antenna including a low noise amplifier connected to the antenna (2, 2.1, 2.2). -Interface module (RFM), analog front-end unit (AFE) including the previous stage radio frequency amplifier (5), and amplified radio frequency signal (f _RF ) directly down-converted to baseband and differential IQ A direct down converter (6) for converting the signal (IQ), a subsequent amplifier (8.1, 8.2) for amplifying and saturating the differential IQ signal (IQ), and the amplified IQ signal (IQ) in bit units. It has a baseband controller (7) that processes directly.

Description

(Field of Invention)
The present invention relates to a receiver for broadband communication, particularly a receiver in a wireless local area network (LAN), and a method for receiving data frames from a wireless device in the wireless local area network.

(Background of the Invention)
In general, a wireless communication system includes modulation of one or more baseband information signals onto one or more carrier signals, transmission of a resulting bandpass signal, and one or more of the above bases at a receiver. Includes demodulation to recover the band information signal. Such a wireless communication system forms part of an electronic device such as a pocket PC (personal computer), a mobile phone, a digital camera, or the like.

  Such communication systems include wideband receivers, which typically employ heterodyne or superheterodyne technology, which are input radio frequency signals (abbreviated as RF signals or carrier frequency signals). Downconverting or upconverting to any convenient intermediate frequency (abbreviated as IF) or directly to baseband (or near zero hertz) and demodulating the IF signal or baseband signal.

  Previous receiver designs, including superheterodyne architecture, required IF filtering and were expensive. A direct conversion zero (none) IF receiver improves these parameters.

US Pat. No. 6230000

  Another simple solution of the conventional direct converter is described in US Pat. No. 6230000. The direct downconverter described in this document is an improvement over conventional direct conversion designs. Specifically, this converter that converts the signal to baseband includes a diverter switch that operates to sample the RF waveform four times per period of the RF frequency. The RF waveform samples are time integrated to produce an average voltage at 0 °, 90 °, 180 ° and 270 °. The average voltage at 0 ° is a baseband in-phase signal, and the average voltage at 90 ° is a baseband quadrature signal.

  An object of the present invention is to define specifications for a wireless LAN, a low-complexity, high-performance, low-power broadband communication receiver and a method for receiving data frames from a wireless device.

  This problem is solved by a broadband receiver comprising the features of claim 1 and by a method comprising the features of claim 12.

  Advantageous embodiments of the invention are described in the respective dependent claims.

(Summary of Invention)
The present invention includes a novel broadband communications receiver based on a direct downconverter as described in US Pat. No. 6230000. In particular, the broadband communication receiver includes an antenna interface module that is connected to an antenna and includes a low noise amplifier that receives and amplifies a radio frequency signal. An analog front-end unit including a radio frequency amplifier and the down-converter is provided, and the received and amplified radio frequency signal is directly down-converted to baseband to obtain a differential IQ signal for the baseband controller. Thereafter, an amplifier amplifies and saturates these differential IQ signals, so that the output terminal of the amplifier is connected directly to the digital input terminal of the baseband controller and the baseband controller The IQ signal is processed in bit units. The advantage of a receiver with such a structure lies in a very simple design by eliminating the conventional analog-to-digital converter. Furthermore, such a receiver has its own exceptional performance with a minimum of components. Thus, such a receiver is very simple, low in complexity, low power and low cost.

  In a preferred embodiment of the invention, the direct downconverter is a product detector, the product detector comprising a conversion switch with a capacitor in response to the amplified radio frequency signal, together with a capacitor, It has two output terminals for integrating a part and generating the differential IQ signal. Such a direct downconverter is described in detail in US Pat. No. 6230000. In particular, the described downconverter has one output that is a 0 ° output for generating a baseband in-phase signal and another output that is a 90 ° output for generating a baseband quadrature signal. It has.

  In another aspect of the present invention, the operation speed of the changeover switch is controlled by a control input signal. The changeover switch is, for example, a four-position rotary switch that is rotated by a control input signal having a frequency equal to four times the frequency of the local oscillator. In a very simple receiver with a simple direct downconverter, it is advantageous that the frequency of the local oscillator is equal to the radio frequency (also called the carrier frequency). In other words, the frequency of the control input signal is equal to four times the radio frequency signal. Since the diversion switch rotates at radio frequency accurately, each capacitor samples the signal once per revolution. This means that each capacitor tracks and tracks the RF amplitude for exactly one quarter of a cycle and retains that value for the remainder of the cycle. The 0 ° and 180 ° capacitors are differentially summed to provide an in-phase signal, and the 90 ° and 270 ° capacitors are summed to provide a quadrature signal.

  In another preferred embodiment, the frequency of the local oscillator is generated by a baseband controller digital-to-analog converter (abbreviated as DAC), the so-called sigma-delta DAC digital output, and subsequent filters, in particular low-pass filters Depends on the control voltage applied. Integration of the local oscillator control loop into the baseband controller is one of the simplest ways to further save cost and power. In particular, active components in the baseband controller can be eliminated.

  In addition, the baseband controller comprises at least one means for phase, time and frequency tracking of the carrier frequency input by evaluating the preamble of the received frame. Again, additional active components in the baseband controller can be eliminated.

  In order to amplify the differential IQ output signal of the down converter, each of the two output terminals of the down converter for the differential IQ signal is connected to an amplifier. This allows the amplified IQ signal to be directly connected to a digital oversampling input pad of a baseband controller (also referred to as a baseband processor). Additional analog-to-digital converters can be eliminated. This simplifies the hardware design of the receiver.

  According to another feature of the invention, the output terminal of each detector is connected to a low pass filter to select the band associated with the digitized input signal for the baseband controller.

  In an alternative preferred embodiment of the present invention, the antenna interface module includes a plurality of antennas, and an antenna switch for selecting one of these antennas in the subsequent stage. Advantageously, this antenna switch is connected to a baseband controller and the associated antenna is determined by a selection signal generated by a selection function (eg diversity selection function) of the baseband controller. This simplifies the hardware design of the receiver.

  In summary, the present invention describes making a broadband receiver low cost, high performance and low power in a flexible and simple manner.

(Detailed description of examples)
Figure 1 shows a schematic block diagram of the entire wideband receiver 1 architecture with an antenna 2 for receiving a radio frequency f _RF. Further, the broadband receiver 1 to be described is applicable to a so-called WLAN receiver designed to operate based on the IEEE802.11b standard. Such a receiver can be part of a consumer product such as a WLAN capable cordless headphone or telephone where transmission and reception range and high data transfer rate are not an issue.

The received radio frequency signal f _RF is amplified by a low noise amplifier 3 connected to the antenna 2. The antenna 2 and the low noise amplifier 3 are components of an antenna interface module RFM (also referred to as a radio frequency unit), for example. The low noise amplifier 3 is, for example, a gain block of about 20 dB and has a noise figure of less than 3 dB.

  The analog front end AFE includes a standard bandpass filter 4 and a buffer amplifier 5, which ensures a constant output impedance of 50 ohms into the subsequent direct downconverter 6. The band pass filter 4 operates in a band of 2400 MHz to 2500 MHz. The buffer amplifier 5 provides excellent element isolation of the direct downconverter 6 with an output impedance of 50 ohms. The downconverter 6 is based on the known direct downconverter described in US Pat. No. 6230000.

The direct down converter 6 down-converts the radio frequency signal f _RF that has been amplified and filtered into a baseband, and converts it into a differential IQ signal for the baseband controller 7 at the subsequent stage. In order to process the IQ signal of the direct downconverter 6, the IQ signal is amplified and saturated by separate amplifiers 8.1 and 8.2. The baseband controller 7 processes the amplified IQ signal in units of bits (for example, despreading, decoding, differential decoding, preamble detection, framing (framing), etc.). In the simplest way, this can be done directly by the baseband processor.

To determine the center of the channel of the direct down-converter 6, to control the converter 6 by a control input signal f _C, the control input signal f _C, the control voltage U _C generated by the digital output of the baseband processor 7 It depends on. Frequency of the control input signal f _C is equal to four times the local oscillation frequency f _LO of the local oscillator 9, the frequency of the local oscillation frequency f _LO is equal to the frequency f _RF of the radio frequency signals (also referred to as carrier frequency).

FIG. 2 shows in more detail a possible embodiment of the architecture of the broadband receiver 1 based on direct down-conversion of the received radio frequency f _RF to baseband.

The received radio frequency signal f _RF enters the receiver 1 through two antennas 2.1, 2.2 and their associated low noise amplifiers 3.1, 3.2. In addition, an optional antenna switch 10 is provided for selecting one of the antennas 2.1 or 2.2. The antenna selection signal S _q is generated by a selection function (eg, a diversity function or other possible selection function) integrated within the baseband controller 7.

The out-of-band signal of the radio frequency signal f _RF is blocked by the standard bandpass filter 4. The bandpass filter 4 can be a known ceramic filter. The signal path up to this point roughly represents a standard front end AFE.

The RF signal f _RF then travels through the buffer amplifier 5 and the role of the buffer amplifier 5 is to ensure a constant output impedance of, for example, 50 ohms into the direct downconverter 6. The output impedance of the amplifier 5 forms a primary low-pass filter together with the capacitors C1 to C4 of the direct down converter 6. The direct downconverter 6 downconverts the RF signal _fRF to baseband to a differential IQ signal, which is then buffer amplified and converted back to single-ended to provide the required selectivity. Through the low-pass filter chains 11.1 and 11.2.

More specifically, direct down-converter 6 are product detector, the change-over switch SS having an input signal in response to the amplified radio frequency signal f _RF comprises with capacitors C1 -C4, a portion of the input signal It has two output terminals A1 and A2 for integrating and generating the differential IQ signal. Specifically, the described down converter 6 has one output A1 that is a 0 ° output for generating a baseband in-phase signal and the other output A2 that is a 90 ° output for generating a baseband quadrature signal. It has.

The conversion switch SS is a four-position rotary switch. The operating speed of the switch SS is controlled by a control input signal f _C. SS is rotated by the control input signal f _C, the frequency of the control input signal f _C is equal to four times the frequency f _LO of the local oscillator. The frequency f _{LO of the} local oscillator is equal to the frequency of the radio frequency signal f _RF (also called the carrier frequency). In other words, the frequency of the control input signal is equal to four times the frequency of the radio frequency signal. Since the SS rotates exactly at the radio frequency f _RF , the capacitors C1 to C4 sample the signal once every rotation. The 0 ° and 180 ° capacitors C1 and C2 are differentially summed to provide an in-phase signal, and the 90 ° and 270 ° capacitors C3 and C4 are summed to provide a quadrature signal.

  The IQ signal outputs A1 and A2 are amplified and, in this example, are amplitude limited and supplied to the baseband controller 7 as a digital signal. The baseband controller 7 performs a sampling task and digitally processes (eg, despreading, CCK (complementary code modulation) decoding, differential decoding, preamble detection, framing, etc.) the resulting bitstream.

The direct downconverter 6 requires a control frequency input f _C that determines the center of the channel. This is generated by the low phase noise oscillator 9. The output frequency or control frequency f _C of the local oscillator 9 is determined by the control voltage U _C generated by the sigma-delta DAC in the baseband processor 7 and the subsequent filter 12, particularly the low-pass filter. The software and hardware in the baseband processor 7 must provide a means to blindly scan all available channels to select one channel and track and record phase and frequency offsets. This can be done, for example, by evaluating the signal preamble of the received frame (which is challenging) or by additional hardware.

  The described receiver 1 represents one possible realization that is extremely simplified, including the following optional and preferred features.

  Additional optimization could possibly be performed by eliminating the conventional PLL divider and phase detector and instead closing the control loop of the carrier oscillator via the baseband controller 7 instead. This structure further saves cost and power.

  In addition, amplifiers 8.1 and 8.2 amplify and saturate the IQ output signal of direct downconverter 6 and connect the output of these amplifiers directly to the digital oversampling input pad of baseband processor 7. Is possible.

(List of reference signs)
DESCRIPTION OF SYMBOLS 1 Receiver 2 Antenna 3 Low noise amplifier 4 Band pass filter 5 Buffer amplifier 6 Direct down converter 7 Baseband controller 8 Amplifier 9 Oscillator 10 Antenna selection switch 11.1, 11.2 Low pass filter 12 Low pass filter f _RF radio frequency Signal f _LO Local oscillation frequency signal f _C Control input signal (frequency signal)
U _C control voltage

1 is a schematic block diagram of the overall architecture of a wideband receiver based on direct down-conversion of received radio frequencies to baseband according to the present invention. FIG. FIG. 6 illustrates a possible embodiment of a wideband receiver architecture based on direct down-conversion of received radio frequencies to baseband.

Claims (20)

In a receiver for broadband communication, especially a receiver for a wireless local area network,
An antenna interface module including a low noise amplifier connected to the antenna;
An analog front end unit including a radio frequency amplifier in the previous stage;
A direct downconverter that directly downconverts the radio frequency signal amplified by the radio frequency amplifier to baseband into a differential IQ signal;
A subsequent amplifier for amplifying and saturating the differential IQ signal;
A broadband communication receiver comprising: a baseband controller that directly processes the amplified differential IQ signal in units of bits.   The direct downconverter is a product detector, the product detector comprising a diverter switch with a capacitor in response to the amplified radio frequency signal, integrating a portion of the input signal; and 2. The broadband communication receiver according to claim 1, further comprising two output terminals for generating the differential IQ signal.   One of the two output terminals is a 0 ° output for generating a baseband in-phase signal, and the other of the two output terminals is a 90 ° output for generating a baseband quadrature signal. The broadband communication receiver according to claim 2, wherein the receiver is a broadband communication receiver.   4. The broadband communication receiver according to claim 2, wherein each of the two output terminals for the differential IQ signal is connected to the amplifier at the subsequent stage. 5.   5. The broadband communication receiver according to claim 2, wherein an operation speed of the conversion switch is controlled by a control input signal.   6. The receiver for broadband communication according to claim 5, wherein the frequency of the control input signal is equal to four times the frequency of a local oscillator, and the frequency of the local oscillator is equal to the frequency of the radio frequency signal.   The receiver for broadband communication according to claim 6, wherein the frequency of the local oscillator is determined by a control voltage generated by a digital-to-analog converter of the baseband controller and a subsequent filter.   8. Each of the two output terminals is connected to a low pass filter for selecting a band associated with the differential IQ signal for the baseband controller. A receiver for broadband communication as described in 1.   The baseband controller comprises at least one means for tracking and recording the phase, time and frequency of the radio frequency signal by evaluating a signal preamble of a received frame. The receiver for broadband communication in any one of 1-8.   The antenna / interface module includes a plurality of antennas, and an antenna switch that is located in a subsequent stage of the plurality of antennas and selects one of the plurality of antennas. The broadband communication receiver according to any one of the above.   The antenna switch is connected to the baseband controller and determines one of the plurality of antennas according to a selection signal generated by a selection function of the baseband controller, for example, a diversity selection function. Item 11. The broadband communication receiver according to Item 10. In a method for receiving a data frame from a wireless device in a wireless local area network,
Receiving a radio frequency signal;
Amplifying the received radio frequency signal;
Downconverting the amplified radio frequency signal directly to baseband to a differential IQ signal;
Amplifying and saturating the differential IQ signal;
A method of receiving a data frame comprising: directly processing the differential IQ signal in units of bits by the baseband controller. Integrating a portion of the input signal in response to the amplified radio frequency signal by a combination of a direct downconverter conversion switch and a capacitor;
13. The method of claim 12, comprising generating the differential IQ signal at two output terminals of the direct downconverter. Generating a baseband in-phase signal with 0 ° output at one of the two output terminals;
14. The method of claim 13, comprising generating a baseband quadrature signal that is 90 ° output at the other of the two output terminals.   15. A method according to claim 13 or 14, comprising connecting each of the two output terminals for the differential IQ signal to an amplifier.   16. A method according to any one of claims 13 to 15, comprising controlling the operating speed of the diversion switch by means of a control input signal.   The method of claim 16, wherein the frequency of the control input signal is equal to four times the frequency of a local oscillator, and the frequency of the local oscillator is equal to the frequency of the radio frequency signal.   The method of claim 17 including determining the frequency of the local oscillator by a control voltage generated by a digital-to-analog converter of the baseband controller and a subsequent filter.   19. The method of claim 13, further comprising connecting each of the two output terminals to a low pass filter for selecting a band associated with the differential IQ signal for the baseband controller. The method of crab.   20. The baseband controller comprising tracking and recording the phase, time and frequency of the radio frequency signal by evaluating a signal preamble of a received frame. The method described.

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