Clamped BJT Clock Buffer for Low-Power Edge Restoration
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Solution Overview
Problem
Conventional clock input buffers for high-performance applications like analog-to-digital converters face challenges with high power consumption due to high slew rates and clock jitter, which are exacerbated by narrow bandpass filtering, leading to inefficient power usage and increased noise.
Innovation Solution
The proposed solution involves a clock buffer design utilizing bipolar junction transistor (BJT) differential pairs and clamps, coupled with current sources and resistors, to achieve high gain while reducing power consumption by optimizing the clock signal processing and output voltage swing levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high gain is used to square-up the input clock edges, then the clock edge definition is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic current control in the differential pair by using a variable tail current source that adjusts the bias current based on the input signal amplitude and frequency. This allows the buffer to use high current (and thus high gain) only when needed for squaring up the clock edges, while reducing current during steady-state operation, thereby resolving the contradiction between edge definition quality and power consumption.
Solution Approach 2:
The patent changes the operating parameters of the differential pair dynamically by adjusting the tail current magnitude and the transistor bias points. The circuit monitors the input signal characteristics and modifies the transconductance and current gain accordingly, enabling high performance during transitions while maintaining low power during stable periods.
2Speed
If high current is drawn to achieve high slew rate, then the clock signal quality is improved, but power consumption increases
Solution Approach 1:
The patent employs periodic switching of the differential pair configuration, alternating between a high-current mode for rapid slewing during clock transitions and a low-current mode for maintaining the output during stable periods. The circuit uses detection circuitry to identify transition moments and activates high slew-rate operation only during these brief intervals, reducing overall power consumption while maintaining signal quality.
Solution Approach 2:
The patent implements dynamic current control in the differential pair by using a variable tail current source that adjusts the bias current based on the input signal amplitude and frequency. This allows the buffer to use high current (and thus high gain) only when needed for squaring up the clock edges, while reducing current during steady-state operation, thereby resolving the contradiction between edge definition quality and power consumption.
3Reliability
If narrow bandpass filtering is applied to reduce clock jitter, then the signal-to-noise ratio is improved, but the input edge rates become slow
Solution Approach 1:
The patent introduces an intermediate stage between the narrow bandpass filter and the output buffer that performs active edge restoration. This intermediate differential pair stage detects the filtered clock signal and actively regenerates sharp edges by utilizing the high-gain differential configuration, effectively decoupling the noise filtering function from the edge rate function and allowing both requirements to be met simultaneously.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design results in a clock buffer that consumes approximately 40% less current and maintains 86% of the output signal amplitude compared to conventional buffers, thereby enhancing efficiency and reducing power consumption.
Implementation Method 1
a first bipolar junction transistor (BJT) differential pair having a first BJT and a second BJT; a second BJT differential pair having a third BJT and a fourth BJT
Implementation Method 2
a first clamp having a fifth BJT and a sixth BJT, wherein the emitters of the fifth and sixth BJTs are coupled to the collectors of the first and third BJTs, and wherein the base of the fifth BJT is adapted to receive a low clamping voltage, and wherein the sixth BJT is adapted to receive a high clamping voltage
Data Source
AI summary
An apparatus is provided. The apparatus comprises a first bipolar junction transistor (BJT) differential pair having a first BJT and a second BJT, a second BJT differential pair having a third BJT and a fourth BJT, a first clamp having a fifth BJT and a sixth BJT, and a second clamp having a seventh BJT and an eighth BJT. The collector and base of the third BJT are respectively coupled to the collector and base of the first BJT, and the collector and base of the fourth BJT are respectively coupled to the collector and base of the second BJT. The bases of first, second, third, and fourth BJTs receive an input clock signal. The emitters of the fifth and sixth BJTs are coupled to the collectors of the first and third BJTs, while the emitters of the seventh and eight BJTs are coupled to the collectors of the second and fourth BJTs. The bases of the fifth and seventh BJT are adapted to receive a low clamping voltage, and the bases of the sixth and eighth BJTs are adapted to receive a high clamping voltage. Additionally, the first and second clamps is coupled to the collectors of the first, second, third, and fourth BJTs.