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When I was simulating a divider using two D-latch as shown below (two D-latches in series,) I found that the circuit in the red rectangular is key to the differential D-latch.

In fact, the circuit in the red rectangular is made up of a forward inverter and an inverted inverter in parallel. If not connecting that circuit, the differential D-latch performs poorly. If connected that circuit, it performs well. If I only use one forward inverter, it still performs poorly.

What is the function of a forward inverter and an inverted inverter in parallel in a digital circuit? What's the principle?

enter image description here

JRE
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shang xu
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  • I have never heard these terms: "Forward inverter" and "Inverted inverter". – Syed Mar 29 '22 at 04:13
  • I don't know how to describe it. For a simple inverter consists of a NMOS and a PMOS, forward means from the gate to drain and inverted means from drain to gate as shown below. – shang xu Mar 29 '22 at 06:17
  • The red rectangle IS the "memory". The other part is only "combinatorial" used as set/reset function. – Antonio51 Mar 29 '22 at 06:37
  • That's right. It functions as a memory element. (Or Stabilize the output) – shang xu Mar 29 '22 at 07:27
  • See https://electronics.stackexchange.com/questions/591677/how-does-an-sr-latch-actually-work/591707#591707 – Antonio51 Mar 29 '22 at 07:45

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These are "cross-coupled inverters" and they form a simple latch storage element. You will see that this is also the heart of a typical static RAM bit. In practice, the sizes of all of the transistors in your latch circuit must be selected carefully for proper electrical behavior.

Elliot Alderson
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