Chapter 11 Frequency Response 11.1 Fundamental Concepts 11.2 High-Frequency Mode
Gilligan, Dave, Midday On-Air Personality has reference to this Academic Journal, PHwiki organized this Journal Chapter 11 Frequency Response 11.1 Fundamental Concepts 11.2 High-Frequency Models of Transistors 11.3 Analysis Procedure 11.4 Frequency Response of CE in addition to CS Stages 11.5 Frequency Response of CB in addition to 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 Chapter Outline CH 11 Frequency Response CH 11 Frequency Response High Frequency Roll-off of Amplifier As frequency of operation increases, the gain of amplifier decreases. This chapter analyzes this problem.
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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. There as long as e phone conversation differs from face-to-face conversation. CH 11 Frequency Response Example: Human Voice II CH 11 Frequency Response 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. Example: Video Signal Video signals without sufficient b in addition to width become fuzzy as they fail to abruptly change the contrast of pictures from complete white into complete black. CH 11 Frequency Response
Gain Roll-off: Simple Low-pass Filter In this simple example, as frequency increases the impedance of C1 decreases in addition to the voltage divider consists of C1 in addition to R1 attenuates Vin to a greater extent at the output. CH 11 Frequency Response CH 11 Frequency Response Gain Roll-off: Common Source The capacitive load, CL, is the culprit as long as gain roll-off since at high frequency, it will steal away some signal current in addition to shunt it to ground. CH 11 Frequency Response Frequency Response of the CS Stage At low frequency, the capacitor is effectively open in addition to the gain is flat. As frequency increases, the capacitor tends to a short in addition to the gain starts to decrease. A special frequency is =1/(RDCL), where the gain drops by 3dB.
CH 11 Frequency Response Example: Figure of Merit This metric quantifies a circuits gain, b in addition to width, in addition to power dissipation. In the bipolar case, low temperature, supply, in addition to load capacitance mark a superior figure of merit. Example: Relationship between Frequency Response in addition to Step Response CH 11 Frequency Response The relationship is such that as R1C1 increases, the b in addition to width drops in addition to the step response becomes slower. CH 11 Frequency Response Bode Plot When we hit a zero, zj, the Bode magnitude rises with a slope of +20dB/dec. When we hit a pole, pj, the Bode magnitude falls with a slope of -20dB/dec
CH 11 Frequency Response Example: Bode Plot The circuit only has one pole (no zero) at 1/(RDCL), so the slope drops from 0 to -20dB/dec as we pass p1. CH 11 Frequency Response Pole Identification Example I CH 11 Frequency Response Pole Identification Example II
CH 11 Frequency Response Circuit with Floating Capacitor The pole of a circuit is computed by finding the effective resistance in addition to capacitance from a node to GROUND. The circuit above creates a problem since neither terminal of CF is grounded. CH 11 Frequency Response Millers Theorem If Av is the gain from node 1 to 2, then a floating impedance ZF can be converted to two grounded impedances Z1 in addition to Z2. CH 11 Frequency Response Miller Multiplication With Millers theorem, we can separate the floating capacitor. However, the input capacitor is larger than the original floating capacitor. We call this Miller multiplication.
CH 11 Frequency Response Example: Miller Theorem High-Pass Filter Response The voltage division between a resistor in addition to a capacitor can be configured such that the gain at low frequency is reduced. CH 11 Frequency Response Example: Audio Amplifier In order to successfully pass audio b in addition to frequencies (20 Hz-20 KHz), large input in addition to output capacitances are needed. CH 11 Frequency Response
Capacitive Coupling vs. Direct Coupling Capacitive coupling, also known as AC coupling, passes AC signals from Y to X while blocking DC contents. This technique allows independent bias conditions between stages. Direct coupling does not. CH 11 Frequency Response Typical Frequency Response CH 11 Frequency Response CH 11 Frequency Response High-Frequency Bipolar Model At high frequency, capacitive effects come into play. Cb represents the base charge, whereas C in addition to Cje are the junction capacitances.
CH 11 Frequency Response High-Frequency Model of Integrated Bipolar Transistor Since an integrated bipolar circuit is fabricated on top of a substrate, another junction capacitance exists between the collector in addition to substrate, namely CCS. CH 11 Frequency Response Example: Capacitance Identification CH 11 Frequency Response MOS Intrinsic Capacitances For a MOS, there exist oxide capacitance from gate to channel, junction capacitances from source/drain to substrate, in addition to overlap capacitance from gate to source/drain.
CH 11 Frequency Response Gate Oxide Capacitance Partition in addition to Full Model The gate oxide capacitance is often partitioned between source in addition to drain. In saturation, C2 ~ Cgate, in addition to C1 ~ 0. They are in parallel with the overlap capacitance to as long as m CGS in addition to CGD. CH 11 Frequency Response Example: Capacitance Identification CH 11 Frequency Response Transit Frequency Transit frequency, fT, is defined as the frequency where the current gain from input to output drops to 1.
Example: IC Amplifier Midb in addition to Design CH 11 Frequency Response Example: IC Amplifier High Frequency Design CH 11 Frequency Response
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