MT-088: Analog Switches and Multiplexers Basics

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MT-088 INPUT SIGNAL LEVEL - V Figure 4: ON-Resistance Versus Input Signal for ADG801/ADG802 CMOS Switch, V DD = +5 V ERROR SOURCES IN THE BASIC CMOS SWITCH It is important to understand the error sources in an analog switch. Many affect ac and dc performance, while others only affect ac. Figure 5 shows the equivalent circuit of two adjacent CMOS switches. The model includes leakage currents and junction capacitances. Figure 5: Equivalent Circuit of Two Adjacent CMOS Switches Page 4 of 23
MT-088 DC errors associated with a single CMOS switch in the on state are shown in Figure 6. When the switch is on, dc performance is affected mainly by the switch on-resistance (R ON ) and leakage current (I LKG ). A resistive attenuator is created by the R G -R ON -R LOAD combination which produces a gain error. The leakage current, I LKG , flows through the equivalent resistance of R LOAD in parallel with the sum of R G and R ON . Not only can R ON cause gain errors—which can be calibrated using a system gain trim—but its variation with applied signal voltage (R ON modulation) can introduce distortion—for which there is no calibration. Low resistance circuits are more subject to errors due to R ON , while high resistance circuits are affected by leakage currents. Figure 6 also gives equations that show how these parameters affect dc performance. Figure 6: Factors Affecting DC Performance for ON Switch Condition: R ON , R LOAD , and I LKG When the switch is OFF, leakage current can introduce errors as shown in Figure 7. The leakage current flowing through the load resistance develops a corresponding voltage error at the output. Leakage current creates error voltage at V OUT equal to: V OUT = I LKG × R LOAD Figure 7: Factors Affecting DC Performance for OFF Switch Condition: I LKG and R LOAD Page 5 of 23
Page 1 and 2: MT-088 TUTORIAL Analog Switches and
Page 3: MT-088 SWITCH DRIVER SWITCH Figure
Page 7 and 8: MT-088 Figure 9: Bode Plot of CMOS
Page 9 and 10: MT-088 Another ac parameter that af
Page 11 and 12: MT-088 Crosstalk is related to the
Page 13 and 14: MT-088 APPLYING THE ANALOG SWITCH S
Page 15 and 16: MT-088 It is important to know how
Page 17 and 18: MT-088 R F = 10kΩ - 625Ω 1.43kΩ
Page 19 and 20: MT-088 The ADG918 is an absorptive
Page 21: MT-088 If diode protection is used,

MT-088: Analog Switches and Multiplexers Basics

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