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(a) Neglecting capacitive effects, calculate the noise figure in decibels of the circuit of Fig. 11.52 with R_{S}= 5 kÎ©. Use data as in Problem 11.10.

(b) If the flicker noise corner frequency for each device is 1 kHz, calculate the low frequency where the spot noise figure is 3 dB above the value in (a).

**Data from Prob. 11.10:**

The ac schematic of a low-input-impedance common-base amplifier is shown in Fig. 11.52.

(a) Calculate the equivalent noise voltage and current generators of this circuit at the emitter of Q_{1} using I_{C1} = I_{C2} = 1 mA, r_{b1} = r_{b2} = 0, Î²_{1} = Î²_{2} = 100, f_{T1} = f_{T2} = 400 MHz. Neglect flicker noise but include capacitive effects in the transistors. Use SPICE to check your result.

(b) If R_{S} = 5 kÎ©, and later stages limit the bandwidth to a sharp cutoff at 150 MHz, calculate the value of i_{S} giving an output signal-to-noise ratio of 10 dB.

**Fig. 11.52:**

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