Differential Output Circuit With Shared Terminals and CMFB Control
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Solution Overview
Problem
The increase in circuit size due to the need for both low voltage differential signaling (LVDS) and single end signaling external output terminals in semiconductor devices.
Innovation Solution
A semiconductor device with a differential amplification circuit, common mode feedback circuit, and switch units that selectively output either differential or single end signals from common external output terminals, reducing the number of external terminals by using a feedback line and resistance elements to control the output mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If both LVDS external output terminals and single end signaling external output terminals are provided in the semiconductor device, then both differential signals and single end signals can be output, but the number of external output terminals increases
Solution Approach 1:
The patent makes the external output terminals universal by enabling them to function in both LVDS differential mode and single-end mode through switch units. The same physical terminals (PD1, PD2) can output either differential signals or single-end signals depending on the switching state, eliminating the need for separate dedicated terminals for each signal type.
Solution Approach 2:
The patent introduces dynamic reconfigurability to the output terminals through switch units (SW1, SW2, SW3) that can change the connection state in real-time. The terminals can dynamically switch between differential output configuration and single-end output configuration, allowing adaptive functionality without increasing terminal count.
2Adaptability or versatility
If switch units are added to control conduction state between output terminals and feedback line, then selective output of differential and single end signals is enabled, but circuit complexity increases
Solution Approach 1:
The patent combines multiple functions into the switch units, which simultaneously control the feedback path and the signal output path. The same switch units (SW1, SW2) that manage feedback line connections also determine whether the output terminals operate in differential or single-end mode, reducing the need for separate control mechanisms.
Solution Approach 2:
The patent implements a feedback mechanism where the common mode feedback circuit (CMFB) monitors the output signals and adjusts the differential amplification circuit accordingly. The feedback line carries common mode voltage information back to the amplification circuit, enabling automatic common mode voltage control and stabilization in both output modes.
Data Source
AI summary
A semiconductor device includes a differential amplification circuit that outputs differential output signals Vo1 and Vo2, external output terminals PD1 and PD2 to which one of the differential output signals Vo1 and Vo2 and single end signals Vo3 and Vo4 is selectively supplied, switch units SW1 and SW2 that control a conduction state between the external output terminal PD1 and the feedback line and a conduction state between the external output terminal PD2 and the feedback line, respectively, resistance elements R1 and R2 respectively provided in series with the switch units SW1 and SW2, a CMFB circuit that controls a common mode voltage of the differential amplification circuit according to a difference between an intermediate voltage Vcm of the external output terminals PD1 and PD2 in the feedback line and a reference voltage Vref, and a switch unit SW3 that controls to supply a clamp voltage to the feedback line.