Fully Differential Operational Amplifiers. Properties of Fully Differential Amplifiers. Small-Signal Models for Balanced Differential Amplifiers. Common-Mode Feedback. Common-Mode Feedback at Low Frequencies. Stability and Compensation Considerations in a CMFB Loop. CMFB Circuits. Fully Differential Op Amps. Unbalanced Fully Differential Circuits. Bandwidth of the CMFB Loop.
Texas Instruments has introduced a fully differential amplifier family that drives high accuracy data conversion across single and multi-channel SAR (successive approximation register) and delta-sigma ADCs (analogue-to-digital converters) in a wide range of applications including industrial, medical and audio. The THS4521, THS4522 and THS4524 provide good performance to power ratio, making the devices suitable for applications requiring high resolution and precision with high dynamic range, such as pressure and flow meters, seismic equipment and electrocardiogram machines, as well as battery-operated devices and other applications with sensitive power budgets. This product family provides an alternative that reduces the number of amplifiers to save board space and alleviates amplifier and circuit matching concerns while minimising power consumption.
The devices consume low quiescent current of 1.14mA per channel and less power down current of 20uA. The family increases the bandwidth by more than 30%, providing 145MHz and 490V/μs slew rate to buffer and amplify signals without increasing the system power consumption. It improves dynamic range/sensitivity by 44% with an input voltage noise of 4.6nV/rtHz to minimise distortion. The output common mode control allows easy DC coupling, while negative rail input and rail-to-rail output capability simplifies design and shortens development time. The device offers power supply flexibility by accepting single supply of +3 to +5V or dual supply of ±1.5 to ±2.5V. The amplifier reduces board space with single, dual and quad configuration options.
The amplifier devices enable customers to drive differential ADCs, including the company's ADS8317 16bit, 250ksamples/s SAR converter and ADS1278 24bit, 128ksamples/s delta-sigma converter and achieve specified data sheet performance levels. For instance, using the THS4521 to buffer the ADS1278, at 10kHz input achieves 102dB SNR (signal-to-noise ratio) and 110dBc SFDR (spurious free dynamic range) with low quiescent current, which reduces system power consumption.