# Chapter 10 - Chapter 10 Control Circuit 1 Low noise...

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1 Chapter 10 Control Circuit

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2 Duplexer Phase Locked Loop Oscillator Low noise amplifier Power amplifier Up- converter Down- converter Rx IF Tx IF Ctrl Bus
3 What’s Microwave Control Circuit A circuit that directs and regulates a process or sequence of events . In this type of circuit, one low frequency or DC signal is made to control a high frequency signal. The general concept of “control” in electronics consists of three main actions: z Starting the flow of a signal z Changing the signal’s property (such as amplitude, or phase) z Stopping the flow of a signal Some of the most important microwave control circuits that perform these functions are: (1) Microwave switches (start and stop action) (2) Microwave phase shifter (phase change action) (3) Microwave attenuator (amplitude change action)

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4 PN Junction Devices (Varactors) Figure 1 shows the equivalent circuit of a varactor diode j C , the junction capacitance p R , parallel equivalent resistance s R , series equivalent resistance s R p R j C Figure 1 The equivalent circuit of a varactor diode
5 A. Reverse Bias The junction capacitance due to the diode’s depletion region becomes dominant in reverse bias. s bi a j j V V C C + = 1 0 (1) 0 j C , the junction capacitance at zero bias voltage a V , the applied reverse bias voltage across voltage across the junction bi V , the built-in voltage 2 1 + = m S , m is the exponent parameter in the doping distribution function ( N ) of the lighter side, defined as: m B x N x N = ) ( (2) B N = An arbitrary constant established by the doping profile.

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6 B. Forward Bias For forward bias, parallel resistor becomes dominant and the corresponding resistance is given by: DC T s I V R / = (3) where DC I is the bias current through the diode, T V is the thermal voltage. For Example: The switching performance of a n + p diode circuit for high-frequency signals can be improved by reducing the electron’s carrier lifetime n τ . The reduction in carrier lifetime will make the forward bias storage capacitance s C small enough to be used in many switching applications
7 PN Junction Devices (PIN Diodes) Figure 2 shows the equivalent circuit of a packaged PIN diode. j C , junction capacitance r R , reverse-biased resistance f R , forward-biased resistance int L , series inductor p L and p C , packaging inductor and capacitor. The equivalent circuits of PIN diode in reverse bias and forward bias are shown in Figure 3. When reverse biased, the junction capacitor dominates the circuits, the diode appears as an open circuit, with a parasitic series capacitor j C . If the diode is forward biased, the junction resistance dominates the circuit. The diode appears as a short circuit with a parasitic series resistance f R . P

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Chapter 10 - Chapter 10 Control Circuit 1 Low noise...

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