An improved common-mode feedback loop for the differential-difference amplifier

Abstract

Unconditional stability of the high-gain amplifiers is a mandatory requirement for a reliable steady-state condition of time-discrete systems, especially for all blocks designed to sample-and-hold (S/H) circuits. Compared to differential path, the common-mode feedback loop is often affected by poles and zeros shifting that degrades the large signal response of the amplifiers. This drawback is made worse in some well-known topologies as the difference-differential amplifier (DDA) that shows non-constant transconductance and poor linearity. This work proposes a body-driven positive-feedback frequency compensation technique (BD-PFFC) to improve the linearity for precision DDA-based S/H applications. Theoretical calculations and circuit simulations carried out in a 0.13 mu m process are also given to demonstrate its validity

Sub-Volt Fully Balanced Differential Difference Amplifier

“…[1][2][3][4][5][37][38][39] The FB-DDA provides the solution for fully di®erential realizations of op-amp circuits where both of the op-amp inputs are°oating. [1][2][3][4][5] Fully di®erential architectures improve performance of analog and mixed analog/digital systems in terms of supply noise rejection, dynamic range, and harmonic distortion and reduce the e®ect of coupling between various blocks. [1][2][3][4][5] However, the existing conventional structures of the FB-DDA become inappropriate to work under sub-volt supply due to the high value of the threshold voltage of the MOS transistors.…”

“…[1][2][3][4][5] Fully di®erential architectures improve performance of analog and mixed analog/digital systems in terms of supply noise rejection, dynamic range, and harmonic distortion and reduce the e®ect of coupling between various blocks. [1][2][3][4][5] However, the existing conventional structures of the FB-DDA become inappropriate to work under sub-volt supply due to the high value of the threshold voltage of the MOS transistors. Hence, alternative design techniques should be adopted.…”