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thông tin mục cụ thể có thể được ghi trực tiếp trên thẻ. Các thông tin sau đó sẽ đi du lịch với mục, chứ không phải là cư trú tại các cơ sở dữ liệu trung tâm. Hình 5-1 cho thấy dòng chảy của thông tin trong một phân cấp so với một hệ thống máy tính điều khiển tập trung. | 216 PROPERTIES PART II EXAMPLE 10.10. At a frequency of 10 kHz an operational amplifier has an input noise voltage v 10 nV ỰĨĨẼ and an input noise current in lOpA ựĩĩĩ both constant within the bandwidth of interest B 100 Hz. It has an amplification A 10 000 and it is operated in the inverting amplifier circuit of Figure 3.2 with Ri 101 ÍÌ and RF lOkfl. Thus the resulting amplification is M 100 and the resistance seen by the operational amplifier at its input terminals is R 100 ÍL The resulting total input noise power per unit bandwidth is given by Equation 10.12 V VỈ _ 10 16V2 Hz 1.6 X 10 20 VA Hz ------- 100ox 1022 A2 Hz 1UU 1.026 X 10 18 VA Hz. The resulting input noise power within the bandwidth B 100 Hz from Equation 10.13 is Bvỉ Pa 100 HzXl.026 X 10 18VA Hz 1.026 X 10 16VA lx and the resulting rms noise voltage at the input from Equation 10.14 is VB x p R 7 1.026 X 10-l6VAX100if 101 nV. The resulting rms noise voltage at the output of the amplifier is Af VB 100X101 nV 10.1 jiV. In many cases the noise performance of an amplifier circuit is described by a noise figure which is a measure of the noise degradation resulting from adding the noise of the operational amplifier to the thermal noise of input resistance R. When the resulting amplification is large M I 1 or MN 1 the noise figure can be approximated by lOdB 1Og10 l 2R - 10.15 It can be shown that the noise figure S has its minimum value min when R Rop u i and it is 10dB logI0 l 10.16 PROBLEMS 217 EXAMPLE 10.11. In Example 10.10 p 10 8 V Hz i 10 A ựHz R 100Q and M 1. Thus from Equation 10.15 and with kT QA X IO 20 VA Hz the noise figure becomes 10dBloglofl lOdB logl0 64.1 18dB. 4kl The minimum noise figure is attained at R R pi v i - 10-8 V ỰhĨI ÍIO 11 A ựĩĩz 1 kíỉ and its value from Equation 10.16 is .0 4 .oaB o4 4544 lOdB log10 13.5 11.3 dB. Above considerations apply equally well to inverting and noninverting amplifiers. In the case of differential amplifiers with signals applied to both inputs the .
