What is Unity incremental gain?
Unity incremental gain is mentioned in relation to two points on the voltage transfer curve: VIH (Voltage Input High) and VIL (Voltage Input Low). These points are described as having “unity incremental gain (slope = –1 V/V).” In the context of a voltage transfer curve, unity gain means that the output voltage changes at the same rate as the input voltage, resulting in a slope of -1.
Noise Margins
- VIH and VIL are defined as the input voltage levels at which the voltage transfer curve has unity incremental gain.
- The noise margin for high input (NMH) is calculated as the difference between the output voltage at VOH (Voltage Output High) and VIH.
- Similarly, the noise margin for low input (NML) is calculated as the difference between the output voltage at VOL (Voltage Output Low) and VIL.
Matching Condition
- There is a mention of an ideal condition where the logic threshold (Vth) is set at the midpoint of the logic swing or VDD/2.
- Matching conditions for nMOS and pMOS transistors are discussed, suggesting that for matched transistors, VIH and VIL occur at the mid-point of the logic swing.
In summary, in the context of this paragraph, “Unity Incremental Gain” refers to the conditions where the voltage transfer curve has a slope of -1 V/V, specifically at VIH and VIL points. These points are crucial in determining the noise margins of the CMOS inverter, which, in turn, are important for the reliable operation of digital circuits.