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Unformatted text preview: CH 10 Differential Amplifiers 1 Chapter 11 Frequency Response 11.1 Fundamental Concepts 11.2 HighFrequency Models of Transistors 11.3 Analysis Procedure 11.4 Frequency Response of CE and CS Stages 11.5 Frequency Response of CB and CG Stages 11.6 Frequency Response of Followers 11.7 Frequency Response of Cascode Stage 11.8 Frequency Response of Differential Pairs 11.9 Additional Examples 1 CH 10 Differential Amplifiers 2 Chapter Outline CH 11 Frequency Response 2 CH 10 Differential Amplifiers 3 CH 11 Frequency Response 3 High Frequency Rolloff of Amplifier As frequency of operation increases, the gain of amplifier decreases. This chapter analyzes this problem. CH 10 Differential Amplifiers 4 Example: Human Voice I Natural human voice spans a frequency range from 20Hz to 20KHz, however conventional telephone system passes frequencies from 400Hz to 3.5KHz. Therefore phone conversation differs from facetoface conversation. CH 11 Frequency Response 4 Natural Voice Telephone System CH 10 Differential Amplifiers 5 Example: Human Voice II CH 11 Frequency Response 5 Mouth Recorder Air Mouth Ear Air Skull Path traveled by the human voice to the voice recorder Path traveled by the human voice to the human ear Since the paths are different, the results will also be different. CH 10 Differential Amplifiers 6 Example: Video Signal Video signals without sufficient bandwidth become fuzzy as they fail to abruptly change the contrast of pictures from complete white into complete black. CH 11 Frequency Response 6 High Bandwidth Low Bandwidth CH 10 Differential Amplifiers 7 Gain Rolloff: Simple Lowpass Filter In this simple example, as frequency increases the impedance of C 1 decreases and the voltage divider consists of C 1 and R 1 attenuates V in to a greater extent at the output. CH 11 Frequency Response 7 CH 10 Differential Amplifiers 8 CH 11 Frequency Response 8 Gain Rolloff: Common Source The capacitive load, C L , is the culprit for gain rolloff since at high frequency, it will “steal” away some signal current and shunt it to ground. 1  out m in D L V g V R C s CH 10 Differential Amplifiers 9 CH 11 Frequency Response 9 Frequency Response of the CS Stage At low frequency, the capacitor is effectively open and the gain is flat. As frequency increases, the capacitor tends to a short and the gain starts to decrease. A special frequency is ω =1/(R D C L ), where the gain drops by 3dB. 1 2 2 2 L D D m in out C R R g V V CH 10 Differential Amplifiers 10 CH 11 Frequency Response 10 Example: Figure of Merit This metric quantifies a circuit’s gain, bandwidth, and power dissipation. In the bipolar case, low temperature, supply, and load capacitance mark a superior figure of merit....
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 Spring '10
 EE
 Frequency, Transistor

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