Assume that a sinusoidal voltage signal is applied to the emitter-coupled pair of Fig. 10.1. Determine the maximum allowable magnitude of the sinusoid such that the magnitude of the third harmonic in the output is less than 1 percent of the fundamental. To work this problem, approximate the transfer characteristic of the pair with the first two terms of the Taylor series for the tanh function. Then assume that all the other harmonics in the output are negligible and that the output is approximately I_out(t) = I_o(sin ω_ot + δ sin 3ω_ot) where δ = fractional third-harmonic distortion. Use SPICE to check your result. For the same sinusoidal input voltage amplitude, use SPICE to find the third harmonic distortion in the output if emitter resistors RE are added to each device such that I_E1R_E= I_E2R_E= 100 mV.

Fig. 10.1

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Q2 Vid LEE