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The Secret of the Transmission Gate: Why Does This Tiny Component Control the Flow of Electric Current?
In today's era of rapid development of electronic equipment, transmission gate, as a crucial component, has gradually received attention. This analog gate, similar to a relay, demonstrates its unique capabilities in the transmission of both analog and digital signals. So, how does this tiny component control the flow of electric current?
Transmission Gate Structure
The transmission gate consists of two field effect transistors (FETs), including an N-type MOSFET and a P-type MOSFET, which are connected in parallel. The most important point of this design is that the bulk terminal is not connected to the source terminal, which makes the signal transmission between input and output smoother.
In a transmission gate, a P-type MOSFET can efficiently transmit 1 but performs poorly in transmitting 0. In contrast, an N-type MOSFET can effectively transmit 0 but performs slightly worse in transmitting 1.
Function of the transmission gate
When the control input is logic zero (negative voltage), the gate of the N-type MOSFET will also be affected by the negative voltage, causing it to not conduct. Conversely, when the control input is logic one, the two MOSFETs begin to transmit signals according to the changes in positive and negative voltages.
This design ensures that no matter which contact the input voltage is, the transmission gate can effectively control the flow of current, thereby turning the signal on or off.
Application of transmission gate
Electronic switch
Transmission gates are ideal for implementing electronic switches and analog multiplexers. Transmission gates can be easily switched when signals need to be routed to different outputs.
Analog Multiplexer
Many mixed-signal systems use analog multiplexers to route multiple analog input channels to a single analog-to-digital converter (ADC). This function can effectively improve the flexibility and efficiency of the system.
Logic Circuits
Transmission gates can also be used to build logic circuits, replacing traditional CMOS pull-up and pull-down networks, an approach that is often more compact in silicon implementation.
Application of negative voltage
When AC voltages (such as audio signals) need to be switched, the transmission gate is designed so that the substrate diode does not conduct, thereby ensuring the validity of the signal flow.
SummaryA good example is the 4053 standard chip, which is commonly used to select between analogue inputs to an audio amplifier.
Transmission gates not only play an indispensable role in many electronic and digital applications, but their flexibility and effectiveness have also promoted the development of many technologies. From electronic switches to analog multiplexers, the potential of these small components continues to be explored. In future electronic designs, will transmission gates become more critical components? Let us think about this possibility together.
