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Dynamic design of large receiver

Paper Keywords: gain linear dynamic STC AGC Abstract: This article describes two ways to expand the dynamic range receiver, as well as in engineering design. Introduction the radar receiver,[link widoczny dla zalogowanych], wide dynamic design is very important. Because in the actual radar signal environment, the receiver frequency band signal into many frequency spectrum, in addition to a useful signal frequency, there is clutter and jamming signal frequency. If the radar receivers is an ideal linear system, these signals are amplified through the receiver, frequency, detection and other transformation, via digital signal processing can be extracted after the target signal. But the receiver is always some degree of non-linear, and because of this nonlinear effect, the received signal spectrum always some changes. For example, into a variety of echo signal receiver intermodulation will have two or more new frequency signal, if the signal generated by non-linear over the threshold and will form a \\Thus, to improve the dynamic range of the receiver is necessary. 2 System Implementation large dynamic system to achieve a large dynamic methods can be divided to achieve a large linear dynamic system, the method and expand the overall dynamic of the method. 2.1 to achieve a large linear dynamic systems approach to achieve a large linear dynamic system, the first method is a reasonable allocation of the gain. Radar receiver system gain by receiver sensitivity, dynamic range and the receiver output signal determined by the treatment. In modern radar receiver,[link widoczny dla zalogowanych], the receiver output of the IF signal or baseband signal normally through A / D converter into digital signals further signal processing. So, when dynamic range and noise figure according to the needs of the receiver, the proper A / D converter,[link widoczny dla zalogowanych], the receiver system gain on the defined. After the receiver gain must determine the reasonable allocation of gain, the gain allocated first to consider the receiver system noise figure. In general, high-frequency low-noise amplifier gain higher than to reduce the post-mixer amplifier and IF amplifier noise impact on system noise figure. However, not high up the gain too high, the amplifier will affect the work of stability, on the other hand will affect the receiver's dynamic range. So, gain, noise figure and dynamic range of the three inter-related and mutually constraining parameters. Here we design a radar receiver in the example to illustrate the gain, noise figure and the relationship between the dynamic range. Receiver noise figure of Fs = 2.OdB, linear dynamic range of 60dB, A / D converter maximum input signal level for the 2vp-p (50S2 load), match the bandwidth of the signal receiver 3.3MHz, receiver threshold sensitivity Psmin (dB / mw) = 1 114dBm + lOlg) f (MHz) + 2dB = 1 107dBm receiver input side of the maximum signal power level for the P },--- 107 +60 =- 47dBm receiver maximum output signal power level for the receiver system gain 57dBo receiver machine of each functional module gain and signal level relations in Figure 1, in the plan, each functional module circuit at the top of the maximum value dBm signal, below the minimum signal difference for the dynamic range. Can see from the picture above,[link widoczny dla zalogowanych], the maximum n mixer input level for a 4dBm, it is easy to achieve; but if the linear dynamic range receiver system requirements for 80dBm, the n the largest mixer input level is changed +16 dBm, this mixer is very difficult. But if the two LNA gain of the reduced SdB, so the maximum input mixer level into + +6 dBm, which becomes possible, and of course have to take care of their gains after reducing the system noise figure effects. Achieve large linear dynamic system, the second method is designed or selected dynamic range of the device. As can be seen from Figure 1, in order to expand the dynamic range of 80dB, IF amplifier 1dB compression point may be increased from SdBm + +15 dBmo addition, in order with the A / D converter interface to match the maximum output signal should be maintained + + lOdBm, then the minimum signal may reach a 70dBm, receiver noise only in the A / D converters accounted for one, which greatly increased the A / D converter design difficult. Solution to this problem: First, to further improve the A / D converter input bits and the maximum level; second IF signal access logarithmic amplifier, after logarithmic compression,[link widoczny dla zalogowanych], then for A / D conversion, This will greatly reduce the A / D converter pressure. 2.2 total receiver dynamic way to expand in modern radar receivers, often require the receiver to a 100dB dynamic range or even higher This requires expanding the receiver, while the linear dynamics, with STC, AGC control circuit to further expand the dynamic range of the receiver. STC attenuator can be used to complete the NC, NC attenuator advantages: first, flexible control, the control signal can be under the radar to determine the clutter around; Second, STC can be set in IF, RF, and even placed in the receiver input side of the feeder, the cause of anti-saturation of the receiver (dynamic range) greatly increased. Figure 2 shows the block diagram of a RF circuit STC.
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