A a diode operating as a rectifier b complete

Info icon This preview shows pages 94–96. Sign up to view the full content.

(a) A diode operating as a rectifier, (b) complete rectifier, (c) input and output waveforms, (d) input/output characteristic. (3.7) (3.8) Thus, the average is proportional to , an expected result because a larger input amplitude yields a greater area under the rectified half cycles. The above observation reveals that the average value of a rectified output can serve as a mea- sure of the “strength” (amplitude) of the input. That is, a rectifier can operate as a “signal strength indicator.” For example, since cellphones receive varying levels of signal depending on the user’s location and environment, they require an indicator to determine how much the signal must be amplified. Example 3.9 A cellphone receives a 1.8-GHz signal with a peak amplitude ranging from 2 V to 10 mV. If the signal is applied to a rectifier, what is the corresponding range of the output average? Solution The rectified output exhibits an average value ranging from 2 V to 10 mV/ mV. Exercise Do the above results change if a 1- resistor is placed in series with the diode?
Image of page 94

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

BR Wiley/Razavi/ Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 70 (1) 70 Chap. 3 Diode Models and Circuits In our effort toward understanding the role of diodes, we examine another circuit that will eventually (in Section 3.5.3) lead to some important applications. First, consider the topology in Fig. 3.11(a), where a 1-V battery is placed in series with an ideal diode. How does this circuit behave? If , the cathode voltage is higher than the anode voltage, placing in reverse bias. Even if is slightly greater than zero, e.g., equal to 0.9 V, the anode is not positive enough to forward bias . Thus, must approach +1 V for to turn on. Shown in Fig. 3.11(a), the I/V characteristic of the diode-battery combination resembles that of a diode, but shifted to the right by 1 V. V I 1 D V I (a) 1 1 V B 1 1 1 V +1 V 1 D V V R 1 out V in out V in 1 t t in V out V V 1 D V B 1 V in R 1 out V t out V in V + V p V p t V p + 1 V V out V in 1 +1 V +1 V (c) (b) Figure 3.11 (a) Diode-battery circuit, (b) resistor-diode circuit, (c) addition of series battery to (b). Now, let us examine the circuit in Fig. 3.11(b). Here, for , remains off, yielding . For , acts a short, and . The circuit therefore does not allow the output to exceed zero, as illustrated in the output waveform and the input/output characteristic. But suppose we seek a circuit that must not allow the output to exceed V (rather than zero). How should the circuit of Fig. 3.11(b) be modified? In this case, must turn on only when approaches +1 V, implying that a 1-V battery must be inserted in series with the diode. Depicted in Fig. 3.11(c), the modification indeed guarantees V for any input level. We say the circuit “clips” or “limits” at +1 V. “Limiters” prove useful in many applications and are described in Section 3.5.3.
Image of page 95
Image of page 96
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern