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single stage amplifiers PDF

289 Pages·2017·2.97 MB·English
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Unit - I SINGLE STAGE AMPLIFIERS Outline – Part II • Noise in analog ICs • Matching in analog ICs • Operational Amplifier design examples • Analog design methodology 2 Thermal noise in passive components Thermal noise is caused by the random thermally excited vibration of the charge carriers in a conductor. v2 Power spectral density [ V 2 / Hz ] n R v2  4kTR  f [ V2 ] n 2 i n 4kT i2   f [ A2 ] n R R There are no sources of noise in ideal capacitors or inductors. In practice, real components have parasitic resistance that does display thermal noise! 3 Noise sources in MOS transistors Channel thermal noise: due to the random thermal motion of the carriers in the channel 1/f noise: due to the random trapping and detrapping of mobile carriers in the traps located at the Si-SiO interface and within the 2 gate oxide. Bulk resistance thermal noise: due to the distributed substrate resistance. Gate resistance thermal noise: due to the resistance of the polysilicon gate and of the interconnections. 4 Noise in circuits To be independent from the gain of a given system, we use the concept of input-referred noise. This allows comparing easily the noise performance of different circuits (with different gains), and calculating easily the Signal-to-Noise Ratio (SNR). At the input of our linear two-port circuit, we use two noise generator (one noise voltage source and one noise current source) to represent the noise of the system regardless the impedance at the input of the circuit and of the source driving the circuit. v2 n,in Noisy Noiseless v2 i2 v2 circuit n,out n,in circuit n,out 5 Input-referred voltage noise The MOS transistor is represented by its small-signal equivalent circuit. We can refer the noise sources inside the MOS transistor to the input, obtaining an input-referred voltage noise. 2 2 v 1 K 1 g in  4kTng  a  4kTR  4kT mb R 2  G 2 B f g C WL f g m ox m Channel thermal Gate resistance Bulk resistance 1/f noise noise thermal noise thermal noise g ideally varies from 1/2 (w.i.) to 2/3 (s.i.) K = 1/f noise parameter, technology dependent a Usually, the first two terms are the most important 6 N-channel noise spectra W = 2 mm, I = 0.5 mA, V = 0.8 V, V = 0 V DS DS BS 1.E-07 L = 0.36um L = 0.5um L = 0.64um L = 0.78um ] ) z L = 1.2um H ( t r q s 1.E-08 / V [ e s i o N 1.E-09 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 Frequency [ Hz ] 7 Noise in a DP + Active CM V V DD DD 2I 2I v2 v2 v2 in in tot i2 i2 out out v2 v2 load load  g2  v2  2  v2  2   m_load   v2 tot in  g2  load   m_in 8 Noise in a DP + Active CM K 1  K  L2  v2  2 a_in  1 a_load load in  f V DD tot_1/f C2 W L f  K  L2    ox in in a_in in load 2I Make W L big and L  L in in load in v2 tot    W       load 2   L   v2  4kTng   1 load  f   tot_th W  W  2 C in I      in ox L  in L   in  in   W   W  Make      L L     in load 9 Outline – Part II • Noise in analog ICs • Matching in analog ICs • Operational Amplifier design examples • Analog design methodology 10

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Noise in circuits. To be independent from the gain of a given system, we use the concept of input-referred noise. This allows comparing easily the noise performance The MOS transistor is represented by its small-signal equivalent circuit. We can .. With single-stage amplifiers it is difficult to o
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