define diode transistor logic as rtls direct answer to its own noise margin problem

# Define Diode-Transistor Logic: RTLs Direct Answer to Its Own Noise-Margin Problem

## 1. Why Swapping Resistors for Diodes at the Input Specifically Fixes the Measured Problem

Diode-transistor logic replaces RTL's input resistors with input diodes feeding a single transistor's base, so that the logic-'0' level presented to that base is set by a diode forward-voltage drop — a value that stays nearly constant regardless of how many downstream loads the previous gate is also driving — directly addressing the fan-out-dependent margin erosion Step 9 measured in RTL. The input stage's own governing behavior:

## 2. Real Diagram: Measured Noise Margin, DTL Against RTL, Same Fan-Out Axis

Repeating Step 9's exact measurement on DTL shows the margin holding far flatter as fan-out rises — the direct, measurable payoff of the diode-clamp change, and the reason DTL displaced RTL in new designs through the mid-1960s even though both remained in production simultaneously for some time.

## 3. Measured Noise Margin, DTL Against RTL, Same Fan-Out Axis

DTL's improved margin came at a real cost in propagation delay, taken up next in Step 11's direct comparison against early PMOS gate delay — DTL's fix for RTL's weakness was not free, and the next step quantifies exactly what it cost.