JP2008160327A - Receiver and receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve phase noise blocking characteristics. <P>SOLUTION: A receiver 100 mixes a local signal in radio frequency signals, creates an intermediate frequency signal and is provided with a control unit 117 which controls a level of the local signal, based on an RSSI (received signal strength indicator). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a receiving apparatus that generates an intermediate frequency signal by mixing a local signal with a radio frequency signal.

FIG. 4 is a diagram showing a configuration of a part of a general receiving circuit. An RF (radio frequency) signal received via an antenna is supplied to a mixer 105 together with a local signal output from an oscillator 104 via a BPF 101, an amplifier 102 and a BPF 103, and converted into an IF (intermediate frequency) signal (Patent Document 1). reference).
JP 2002-76969 A

  One of the performance evaluation items of the receiving circuit is a phase noise blocking characteristic. When a strong proximity signal is received, the sideband noise of the receiver increases, and a weak signal is blocked by the noise. The level of the increased noise is a phase noise blocking characteristic. Hereinafter, factors that cause phase noise blocking will be described.

  FIG. 5 is a diagram showing the proximity characteristics of the received signal, where the vertical axis indicates the output level and the horizontal axis indicates the frequency. In the figure, f0 indicates the center frequency of the local signal, but there is also a power component due to phase noise at the detuning frequency f0-Δf that is separated from the center frequency f0 by Δf, and this power component is input to the mixer. A power component is generated at the output of the mixer. This power component is phase noise blocking.

  FIG. 6 is a diagram showing the output characteristics of the mixer. The vertical axis shows the conversion gain, and the horizontal axis shows the level of the local signal. In the case of the illustrated mixer, the conversion gain characteristic saturates when the input local level exceeds 0 [dBm]. In consideration of element variation and temperature characteristics, it is preferable to use at about +2 to +5 [dBm]. Generally, the local signal level is set to an optimum value from the conversion gain and linearity. However, as shown in FIG. 5, the conversion gain is greatly reduced and becomes unstable when the level is below a certain level. It is necessary to input a signal having a level at which the gain is sufficiently saturated to the mixer.

  By supplying the RF signal (frequency A [MHz]) and the local signal (frequency B [MHz]), the mixer has two frequency components (A−B = C [MHz], A + B = D [MHz]). Will occur. The frequency component C or D is selected by the downstream narrowband filter and supplied to the downstream circuit as an intermediate frequency which is a desired frequency. Hereinafter, the frequency component C is set as an intermediate frequency. When the frequency component C is generated by the power component of the detuning frequency f0-Δf shown in FIG. 5, it becomes a noise component and generates interference. When Δf is E, a relationship of A + E−B−E = C [MHz] is established, and a frequency component C is generated. The frequency A + E is an interference frequency that causes blocking. E must be considered as all frequencies existing in the band of the system, and the blocking characteristic is a very important factor that determines the quality of the received signal.

  In general, as shown in FIG. 6, the local signal is input to the mixer after the conversion gain is sufficiently saturated and the conversion gain does not change due to temperature or the like. If the level of the local signal is high, a low level signal can be received, but if the reception state is good, sufficient characteristics can be secured even if the level of the local signal is lowered (see FIG. 7). By lowering the level of the local signal, the level of the center frequency f0 is lowered, but the level of the detuning frequency f0-Δf is also lowered, so that phase noise generated by blocking is reduced.

  Taking the mixer having the characteristics shown in FIG. 6 as an example, when the standard input level is set to +5 [dBm], the conversion gain does not decrease until 0 [dBm], which is a local signal level decreased by 5 [dBm]. Therefore, it can be considered that there is no influence of the main signal due to the local signal level being lowered by 5 [dBm]. When the local signal level is −10 [dBm], the conversion gain decreases. Therefore, the power component due to the phase noise output from the mixer can be reduced by reducing the local signal level.

  FIG. 7 shows phase noise characteristics, where the vertical axis indicates the input level and the horizontal axis indicates the frequency. When attention is paid to the detuning frequency f0-Δf that is Δf away from the center frequency f0 of the local signal, attenuation of C / N is expected from the characteristics of the PLL and VCO, so the conversion gain of the mixer is sufficiently lowered from the saturation level. The attenuation range has been reached. Therefore, it can be considered that if the local signal level is lowered by 5 [dBm], the conversion gain corresponding to 5 [dBm] is lowered. From the above characteristics, even when the local signal level is lowered by 5 [dBm], the output level at the detuning frequency can be lowered while maintaining the output level of the main signal mixer.

  Further, as a method for improving phase noise blocking, attention may be paid to VCO, PLL, and BPF. However, the phase noise characteristic is limited due to the characteristics of the VCO and PLL. In recent years, a high-speed lockup is required for the PLL, and it is necessary to widen the loop bandwidth. However, if the loop bandwidth is widened, the phase noise cannot be improved with respect to the detuning frequency. Furthermore, there is a limit to the characteristics of the narrow band BPF.

  The present invention provides a receiving device that generates an intermediate frequency signal by mixing a local signal with a radio frequency signal, and includes control means for controlling the level of the local signal based on the strength of the received signal. The present invention further comprises a control step of controlling the level of the local signal based on the strength of the received signal in a receiving method for generating an intermediate frequency signal by mixing a local signal with a radio frequency signal. According to this configuration, it is possible to reduce the phase noise without reducing the C / N characteristic of the intermediate frequency by changing the level of the local signal in consideration of the strength of the received signal, and the phase noise blocking characteristic is improved. Can be improved.

  Specifically, the intensity of a predetermined received signal necessary for obtaining the signal quality required for the intermediate frequency signal for each modulation method is compared with the intensity of the received signal of the received intermediate frequency signal. When the intensity of the received signal of the intermediate frequency signal is greater than the intensity of the predetermined received signal, the level of the local signal is controlled so that the intensity of the received signal of the received intermediate frequency signal approaches the intensity of the predetermined received signal To do.

  In the present invention, the level of the local signal can be controlled by the amplification gain of the amplifier, or the level of the local signal can be controlled by the attenuation gain of the attenuator.

  FIG. 1 is a diagram showing a configuration of a receiving apparatus according to an embodiment of the present invention. The received signal is supplied to the mixer 105 together with the output of the oscillator 104 via the BPF 101, the amplifier 102 and the BPF 103. The output of the oscillator 104 is amplified by the variable gain amplifier 105, band-limited by the BPF 106, and then supplied to the mixer 105. The output of the mixer 105 is amplified by the amplifier 108 via the BPF 107 and then supplied to the mixer 110 together with the output of the oscillator 109. The output of the oscillator 109 is amplified by the amplifier 111 and then supplied to the mixer 110 via the BPF 112. The output of the mixer 110 is amplified by the variable gain amplifier 115 via the amplifier 113 and the BPF 114 and then demodulated by the demodulator 116.

  The control unit 117 controls the amplification gain of the variable gain amplifier 105 based on the RSSI (received signal strength indication signal) of the IF signal detected by the demodulation unit 116, and controls the level of the local signal. Specifically, when the detected RSSI is larger than a preset threshold (predetermined RSSI), it is determined that the reception state is good, and the input level is lowered until the RSSI becomes equal to the threshold. The threshold value indicates a value necessary for obtaining the C / N required for the IF signal. Since the C / N differs for each modulation method, the threshold value is set for each modulation method (see Table 1).

  FIG. 2 shows BER characteristics for each modulation method, where the vertical axis indicates BER and the horizontal axis indicates C / N (theoretical value). For example, in order to achieve BER (bit error rate) = 0.001% when performing communication with 64QAM, a C / N of 26 dB is theoretically required. The required C / N increases as the modulation class increases. Accordingly, the threshold is set so that C / N corresponding to the modulation class is obtained. In addition, the threshold value shown in Table 1 uses a receiver having a received signal passband of 300 [kHz], a receiver NF of 3.0 [dB], and a noise level of −116.06 [dBm] under the condition of 27 ° C. A value set with reference to a point of BER = 0.001% is shown.

  FIG. 3 is a diagram showing a flow of processing of the control unit 117. First, the modulation scheme of the received signal is detected (S101), and the RSSI threshold is determined for each modulation scheme (S102). Thereafter, the RSSI of the received signal is detected (S103), and the RSSI of the received signal is compared with the threshold value determined for each modulation method (S104). When the RSSI of the received signal is equal to or higher than the threshold value determined for each modulation method (S104: Yes), the local signal level is controlled to be lowered (S105), otherwise (S104: No), the local signal level is controlled. The signal level is held (S106).

  According to the above embodiment, by changing the level of the local signal in consideration of RSSI, it becomes possible to reduce the phase noise without lowering the C / N characteristic of the IF signal, thereby improving the phase noise blocking characteristic. be able to. In addition, the phase noise can be improved at a lower cost compared to the case where the phase noise is improved by VCO, PLL, and BPF.

The figure which shows the structure of the receiver which concerns on embodiment of this invention Diagram showing BER characteristics The figure which shows the flow of processing of a control part The figure which shows the constitution of the receiving circuit Diagram showing the proximity characteristics of the received signal Diagram showing the output characteristics of the mixer Diagram showing phase noise characteristics

Explanation of symbols

100 Receiver 101, 103, 107, 114 BPF
102, 108, 113 Amplifier 104, 109 Oscillator 105 Variable gain amplifier 105, 110 Mixer 115 Amplifier 116 Demodulator 117 Control unit

Claims (7)

  A receiving apparatus that mixes a local signal with a radio frequency signal to generate an intermediate frequency signal, the receiving apparatus comprising control means for controlling the level of the local signal based on the strength of the received signal.   The control means compares the strength of a predetermined received signal necessary to obtain the signal quality required for the intermediate frequency signal with the strength of the received signal of the received intermediate frequency signal, and 2. The level of the local signal is controlled so that the received signal strength of the received intermediate frequency signal approaches the predetermined received signal strength when the received signal strength is greater than the predetermined received signal strength. The receiving device described.   The receiving apparatus according to claim 2, wherein the control unit compares the intensity of the predetermined reception signal set for each modulation method with the intensity of the received signal of the received intermediate frequency signal.   The receiving apparatus according to claim 1, wherein the control unit controls the level of the local signal by an amplification gain of an amplifier.   The receiving apparatus according to claim 1, wherein the control unit controls the level of the local signal by an attenuation gain of an attenuator.   A receiving method for generating an intermediate frequency signal by mixing a local signal with a radio frequency signal, comprising a control step of controlling the level of the local signal based on the strength of the received signal. The control step compares the intensity of a predetermined received signal necessary for obtaining the signal quality required for the intermediate frequency signal for each modulation method and the intensity of the received signal of the received intermediate frequency signal; When the received signal strength of the received intermediate frequency signal is greater than the predetermined received signal strength,
The reception method according to claim 6, further comprising: controlling a level of the local signal so that a received signal intensity of the received intermediate frequency signal approaches an intensity of the predetermined received signal.

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