Sample-and-Hold Amplifier With Push-Pull Rail-to-Rail Output
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Solution Overview
Problem
Existing sample and hold circuits face challenges in achieving a rail-to-rail output swing due to limitations in transistor parameter variations, leading to reduced signal-to-noise ratio and increased power consumption.
Innovation Solution
A sample and hold circuit design that includes a push-pull differential amplifier with split sampling capacitors and separate bias voltages for NMOS and PMOS transistors, enabling extended output signal swing by decoupling bias voltages from transistor parameter variations and allowing operation in a rail-to-rail mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the operating current is increased to compensate for thermal noise, then the signal-to-noise ratio is improved, but the power consumption increases significantly
Solution Approach 1:
The patent changes the operating voltage parameter to enable rail-to-rail output swing, allowing the circuit to operate across the full supply voltage range. This parameter change allows the use of lower operating currents while maintaining adequate signal-to-noise ratio, thereby reducing power consumption.
2Temperature
If the available headroom of active transistors is reduced due to technology scaling, then the circuit can operate at lower voltages, but the analog signal range is reduced
Solution Approach 1:
The patent segments the output swing range into two parts: one handled by NMOS transistors and another by PMOS transistors in a push-pull configuration. This segmentation allows each transistor type to operate in its optimal region while collectively achieving rail-to-rail output swing, thus maintaining full signal range even at reduced operating voltages.
Solution Approach 2:
The patent uses a composite transistor configuration combining both NMOS and PMOS devices in a push-pull differential amplifier. This composite structure leverages the complementary strengths of both transistor types to achieve extended output swing that neither transistor type could achieve alone, effectively overcoming the headroom limitations of scaled technologies.
3Length of moving object
If separate bias voltages are used for NMOS and PMOS transistors, then the output signal swing is extended to rail-to-rail, but the circuit complexity increases
Solution Approach 1:
The separate bias voltage circuits serve multiple functions: they establish the appropriate operating points for NMOS and PMOS transistors, enable rail-to-rail output swing, and provide independent optimization for each transistor type. This multi-functionality justifies the additional complexity by achieving performance that cannot be obtained with a single bias voltage.
Data Source
AI summary
A sample and hold circuit providing rail-to rail equivalent output is described. The circuit includes a sample and hold amplifier containing two separate sets of sampling capacitors, one set is coupled to a PMOS transistor differential stage and the other set is coupled to an NMOS transistor differential stage. The differential stages drive a current mirror based push-pull output differential stage to provide an output signal with ranges equivalent to a rail-to rail output signal swing.