Transmission Gates Question & Answers July 31, 2026 By WatElectronics Transmission gates are one of the most fundamental building blocks in CMOS and VLSI circuit design. They function as bidirectional electronic switches, enabling efficient transfer of both digital and analog signals with minimal signal degradation. Unlike a single NMOS or PMOS pass transistor, a transmission gate combines one NMOS and one PMOS transistor connected in parallel and controlled by complementary signals. This complementary configuration allows the transmission gate to pass both logic HIGH and logic LOW levels effectively, making it an ideal choice for high-performance, low-power integrated circuits. Transmission gates are widely used in digital electronics and mixed-signal applications, including multiplexers, demultiplexers, latches, flip-flops, sample-and-hold circuits, switched-capacitor filters, memory circuits, and bus switching networks. Their ability to provide rail-to-rail signal transmission, low ON resistance, high OFF resistance, and bidirectional operation has made them indispensable in modern CMOS technology. Understanding the principles, operation, advantages, limitations, and applications of transmission gates is essential for students, engineers, and researchers working in digital electronics, VLSI design, and semiconductor technology. This collection of 100 multiple-choice questions (MCQs) has been carefully designed to strengthen conceptual understanding of transmission gates. The questions range from basic concepts to advanced applications, covering device operation, circuit analysis, design considerations, and practical implementations. Each MCQ includes the correct answer, a helpful hint, and a detailed explanation, making this resource suitable for self-assessment, classroom learning, competitive examinations, and technical interview preparation. 1). What is a transmission gate? A logic gate used only in TTL circuits A bidirectional switch made using parallel NMOS and PMOS transistors A memory element An amplifier None Hint 2). A transmission gate consists of? Two NMOS transistors Two PMOS transistors One NMOS and one PMOS transistor One BJT and one MOSFET None Hint 3). Why is a PMOS added with an NMOS in a transmission gate? To reduce chip area To improve current gain To pass strong logic '1' and logic '0' To increase capacitance None Hint 4). The control signals for a transmission gate are? Same signals to NMOS and PMOS Complementary signals Random signals Clock signals only None Hint 5). When the control input is HIGH, a transmission gate? Opens Disconnects Conducts Oscillates None Hint 6). A transmission gate behaves like? Capacitor Resistor when ON Inductor Transformer None Hint 7). Transmission gates are mostly fabricated using? TTL technology CMOS technology ECL technology RTL technology None Hint 8). Which logic level is passed weakly by NMOS? Logic 0 Logic 1 Both None None Hint 9). PMOS passes a weak: Logic 1 Logic 0 Both None None Hint 10). Main advantage of a transmission gate? High power consumption Bidirectional operation Large area Slow speed None Hint 11). Transmission gates are used in? Multiplexers Registers Latches All of these None Hint 12). OFF state resistance of a transmission gate is? Low Moderate Very high Zero None Hint 13). Which transistor gets inverted control? NMOS PMOS Both Neither None Hint 14). Transmission gates are especially useful in? Analog switching Digital switching Mixed-signal circuits All of these None Hint 15). The symbol of a transmission gate resembles? Amplifier Controlled switch Capacitor Diode None Hint 16). The major drawback of a single NMOS switch is? High power Weak logic 1 Large area Noise None Hint 17). The transmission gate removes? Body effect completely Threshold voltage loss significantly Power loss entirely Delay entirely None Hint 18). A transmission gate is? Unidirectional Bidirectional Directional only Fixed direction None Hint 19). Which application commonly uses transmission gates? Multiplexer Flip-flop Sample-and-hold circuit All of these None Hint 20). Number of control signals needed? 1 2 complementary signals 3 4 None Hint 21). Transmission gate is equivalent to? Ideal switch approximation Diode Capacitor Battery None Hint 22). In TG-based MUX, transmission gates replace? Resistors Diodes Logic gates Mechanical switches None Hint 23). Which transistor has higher mobility? PMOS NMOS Both same Depends None Hint 24). PMOS compensates for? NMOS weak HIGH NMOS weak LOW Power loss Noise None Hint 25). TGs reduce? Voltage degradation Power supply Frequency Noise margin None Hint 26). Which characteristic makes a transmission gate superior to a single NMOS pass transistor? Higher threshold voltage Lower input capacitance Ability to pass both logic HIGH and logic LOW without significant degradation Larger transistor size None Hint 27). Which transistor primarily passes a strong logic '0'? PMOS NMOS BJT CMOS Inverter None Hint 28). Which transistor primarily passes a strong logic '1'? NMOS PMOS Diode JFET None Hint Transmission Gates MCQs for Interviews 29). A transmission gate requires how many MOS transistors? One Two Three Four None Hint 30). Which signal controls the PMOS transistor in a transmission gate? Clock Enable Complement of the control signal Ground None Hint 31). What happens when the control input of a transmission gate is LOW? Only NMOS conducts Only PMOS conducts Both transistors are OFF Both transistors are ON None Hint 32). Which property allows transmission gates to carry analog signals? High gain Bidirectional low-resistance path Current amplification Voltage multiplication None Hint 33). A transmission gate behaves like an open circuit when? Both transistors are ON Control is HIGH Both transistors are OFF Input is HIGH None Hint 34). The ON resistance of a transmission gate depends mainly on: Supply voltage Temperature MOS transistor dimensions Crystal frequency None Hint 35). Increasing the width of both transistors in a transmission gate will generally? Increase ON resistance Reduce ON resistance Stop conduction Increase threshold voltage None Hint 36). In digital circuits, transmission gates are widely used to implement? Oscillators only Amplifiers only Multiplexers Voltage regulators None Hint 37). Which feature makes transmission gates ideal for multiplexers? High voltage gain Low leakage in OFF state and low resistance in ON state High power dissipation Large propagation delay None Hint 38). Which of the following is NOT an application of transmission gates? Sample-and-hold circuits CMOS latches Voltage amplification Multiplexers None Hint 39). Why are transmission gates preferred over mechanical switches in ICs? They require moving parts They switch electronically They consume more power They generate magnetic fields None Hint 40). In a transmission gate, current can flow? Only from source to drain Only from drain to source In either direction Only toward ground None Hint 41). Which logic family commonly uses transmission gates? TTL CMOS DTL RTL None Hint 42). What is the primary purpose of using complementary control signals? Reduce frequency Ensure both MOSFETs switch simultaneously Increase resistance Increase threshold voltage None Hint 43). A transmission gate can transfer: Digital signals only Analog signals only Both analog and digital signals Power signals only None Hint 44). Which statement is TRUE regarding threshold voltage loss? NMOS passes strong HIGH PMOS passes strong LOW Transmission gate minimizes threshold voltage loss Threshold voltage loss increases in transmission gates None Hint 45). A transmission gate is controlled using: One control signal only Two independent clocks A control signal and its complement Analog voltage only None Hint 46). Which factor directly affects the propagation delay through a transmission gate? Ambient light ON resistance and load capacitance Number of LEDs Supply frequency only None Hint 47). In CMOS latch circuits, transmission gates mainly function as: Oscillators Controlled switches Voltage amplifiers Rectifiers None Hint 48). Why is a transmission gate considered bidirectional? It amplifies both positive and negative signals It allows signals to pass in either direction It uses two power supplies It contains two outputs None Hint 49). Which parameter is improved by using a transmission gate instead of a single MOS pass transistor? Voltage swing Clock frequency Memory size Chip temperature None Hint 50). Which statement best summarizes the operation of a transmission gate? It amplifies signals using complementary MOS transistors. It stores digital information permanently. It acts as a bidirectional CMOS switch controlled by complementary signals. It converts analog signals into digital signals. None Hint Transmission Gates MCQs for Exams 51). Which type of multiplexer commonly uses transmission gates in CMOS design? Magnetic multiplexer Optical multiplexer CMOS 2:1 Multiplexer Mechanical multiplexer None Hint 52). In a transmission gate, both NMOS and PMOS transistors are connected in: Series Parallel Cascade Bridge configuration None Hint 53). What is the primary reason for using transmission gates in sample-and-hold circuits? Voltage amplification Signal switching with low distortion Frequency multiplication Current amplification None Hint 54). Which logic level experiences the greatest degradation through a single NMOS pass transistor? Logic LOW Logic HIGH Both equally Neither None Hint 55). Which logic level experiences the greatest degradation through a single PMOS pass transistor? Logic HIGH Logic LOW Both equally Neither None Hint 56). A transmission gate can be considered an ideal switch because it has? Infinite gain Low ON resistance and high OFF resistance Zero capacitance Infinite bandwidth None Hint 57). Which digital storage element commonly incorporates transmission gates? Counter CMOS Latch Decoder Encoder None Hint 58). In CMOS technology, a transmission gate primarily improves: Logic voltage swing Power supply voltage Clock frequency Package size None Hint 59). Which transistor characteristic mainly determines the ON resistance? Gate oxide color Channel width Package type Crystal orientation None Hint 60). When both transistors in a transmission gate conduct simultaneously, the signal path becomes: High resistance Open circuit Low resistance Capacitive only None Hint 61). Which CMOS circuit relies heavily on transmission gates for data selection? Multiplexer Oscillator Regulator Comparator None Hint 62). The bidirectional nature of transmission gates is useful because? Signals can travel in either direction They amplify signals They generate clock pulses They reduce transistor count to one None Hint 63). Which control signal combination turns OFF a transmission gate? NMOS = HIGH, PMOS = LOW NMOS = LOW, PMOS = HIGH NMOS = HIGH, PMOS = HIGH NMOS = LOW, PMOS = LOW None Hint 64). In a CMOS transmission gate, the body terminal of the NMOS is generally connected to? VDD Ground Output Input None Hint 65). In a CMOS transmission gate, the body terminal of the PMOS is generally connected to? Ground Output Input VDD None Hint 66). Transmission gates are preferred in CMOS logic because they? Require external resistors Pass rail-to-rail voltage levels Need bipolar transistors Consume high static power None Hint 67). Which parameter primarily determines the delay through a transmission gate? Ambient humidity RC time constant Light intensity Crystal frequency None Hint 68). Which application commonly uses transmission gates for charge transfer? Switched-capacitor circuits Transformers Induction motors Voltage regulators None Hint 69). What happens if complementary control signals are not provided? Both transistors always remain ON Improper switching may occur Output becomes amplified ON resistance becomes zero None Hint 70). Compared to a single MOS pass transistor, a transmission gate offers? Reduced voltage degradation Larger threshold voltage Higher leakage current Lower switching speed None Hint 71). In a transmission gate, signal flow is blocked when? Both transistors are OFF Both transistors are ON Only NMOS is ON Only PMOS is ON None Hint 72). Which VLSI design style frequently uses transmission gates to reduce transistor count? Pass-transistor logic RTL DTL TTL None Hint 73). A transmission gate provides better signal integrity because it? Amplifies the input Restores supply voltage Minimizes logic-level degradation Filters high-frequency noise None Hint 74). Which statement best describes the OFF-state behavior of a transmission gate? It behaves like a low-value resistor. It behaves like a short circuit. It behaves like a high-impedance switch. It behaves like a voltage source. None Hint 75). Why are transmission gates widely used in modern VLSI systems? They increase static power consumption. They require only NMOS transistors. They provide efficient, low-power, bidirectional switching with minimal signal loss. They eliminate the need for CMOS technology. None Hint Transmission Gates MCQs for Quiz 76). Which CMOS logic style makes extensive use of transmission gates? Static CMOS Logic Transmission Gate Logic (TGL) Diode Logic Emitter-Coupled Logic (ECL) None Hint 77). In a transmission gate, the NMOS transistor conducts best when passing: Logic HIGH Logic LOW Floating voltage AC signals only None Hint 78). Which property makes transmission gates suitable for analog multiplexers? High voltage gain Low distortion and bidirectional conduction Current amplification High output impedance None Hint 79). A transmission gate is primarily controlled by? Current source Complementary digital control signals Analog comparator Pulse transformer None Hint 80). Which parameter mainly determines the current-driving capability of a transmission gate? Gate oxide thickness only Transistor width (W) Package material Crystal oscillator frequency None Hint 81). When a transmission gate is ON, its equivalent electrical model is closest to? Open circuit Low-value resistor Ideal voltage source Capacitor None Hint 82). Which of the following is a major advantage of transmission gates over relay switches? Mechanical operation Faster switching speed Larger physical size Higher maintenance None Hint 83). In a CMOS D-latch, transmission gates are mainly used to: Increase supply voltage Control the flow of input data Amplify stored data Generate clock pulses None Hint 84). Which of the following best describes the OFF-state leakage current of an ideal transmission gate? Very high Zero or extremely small Equal to ON current Infinite None Hint 85). A transmission gate is commonly used in which memory element? SRAM cell EEPROM only PROM only Magnetic memory None Hint 86). The propagation delay of a transmission gate decreases when? ON resistance decreases Load capacitance increases Supply voltage decreases significantly Leakage current increases None Hint 87). Which transistor parameter has the greatest effect on ON resistance? Threshold voltage alone Width-to-Length (W/L) ratio Package type Operating temperature only None Hint 88). Why is a transmission gate called a bilateral switch? It has two outputs. It allows current flow in both directions. It uses two batteries. It contains two capacitors. None Hint 89). Which digital circuit uses transmission gates to implement efficient XOR functions? Transmission Gate Logic RTL DTL PMOS Logic None Hint 90). In a transmission gate, increasing transistor width generally results in? Higher ON resistance Lower ON resistance Higher threshold voltage Reduced conductivity None Hint 91). Which statement is TRUE regarding signal direction in a transmission gate? Signals travel only from source to drain. Signals travel only from drain to source. Signals can travel in either direction. Signals require a diode for reverse flow. None Hint 92). Which application requires transmission gates for periodic charging and discharging of capacitors? Switched-capacitor filters Linear regulators Power amplifiers Crystal oscillators None Hint 93). What is the primary reason for using complementary MOS transistors in a transmission gate? Increase transistor count Eliminate threshold voltage degradation Increase power consumption Reduce switching speed None Hint 94). Compared with a single MOS pass transistor, a transmission gate provides? Better voltage transfer characteristics Lower operating frequency Greater threshold voltage drop Reduced switching capability None Hint 95). Which of the following is NOT a typical application of transmission gates? CMOS Multiplexer Sample-and-Hold Circuit CMOS Latch High-Gain Operational Amplifier None Hint 96). During normal operation, the PMOS transistor in a transmission gate receives: The same control signal as NMOS The complement of the NMOS control signal Ground only Analog input voltage None Hint 97). Which characteristic contributes most to the low-power operation of transmission gates in CMOS technology? Continuous current flow Negligible static power consumption High leakage current High operating temperature None Hint 98). Which statement best describes the role of transmission gates in clocked circuits? They generate the clock. They amplify the clock. They control the timing of data transfer. They stabilize the power supply. None Hint 99). Which of the following best explains why transmission gates are preferred in modern VLSI design? They require bipolar transistors. They occupy unlimited chip area. They provide efficient switching with low power and minimal signal degradation. They eliminate the need for CMOS fabrication. None Hint 100). Which statement BEST summarizes the function of a CMOS transmission gate? It is a voltage amplifier used in analog circuits. It is a bidirectional electronic switch composed of one NMOS and one PMOS transistor controlled by complementary signals. It is a memory cell that permanently stores binary data. It is a current source used in digital logic. None Hint Transmission gates play a crucial role in the design of modern CMOS and VLSI circuits by providing an efficient means of transferring signals with high reliability and minimal loss. Their complementary NMOS-PMOS structure allows them to overcome the limitations of individual pass transistors, making them an essential component in a wide range of digital and mixed-signal applications. As integrated circuits continue to evolve toward higher speed, lower power consumption, and greater complexity, the importance of transmission gates in achieving these design goals continues to grow. The set of 100 multiple-choice questions presented in this article is intended to serve as a practical learning and assessment tool for students, educators, and professionals. By progressing through questions of varying difficulty and reviewing the accompanying hints and explanations, readers can strengthen their conceptual understanding, identify areas requiring further study, and improve their analytical and problem-solving skills. Mastering transmission gate concepts not only enhances knowledge of switching circuits but also provides a solid foundation for understanding more advanced topics in CMOS logic design, pass-transistor logic, memory architectures, clocking circuits, and mixed-signal systems. Regular practice with concept-based MCQs, combined with circuit analysis and practical design exercises, will help learners develop the confidence and expertise required for academic success, competitive examinations, and careers in electronics and VLSI engineering. Time's up
