单端信号转差分信号-方法介绍.pdfVIP

Combining Input Amplifiers and Converters for Frequency Domain Applications Vera Mao Texas Instruments All High Speed, High Performance ADCs have Differential Inputs • Drive amplifier circuit needs to provide differential inputs • If input signal is single ended, must convert to differential – Can be done with single ended Amps and transformers – Can be done with FDA (Fully Differential Amplifiers) • Better performance if input signal is differential Single Ended amp with transformer interface Two factors limit this approach • Amplifier (often not present) – Single-ended architecture must consume a great deal of power to keep HD2 components low. • Transformer – If no amplifier, then limited choices in voltage gain (via turns ratio) – Limits low frequencies – Pass-band flatness can be an issue because of ripple. Transformers - Will not pass DC signals and losses vary over the pass-band Example 1: High BW balun Example 2: Isolation Transformer Macom ETC1-13 Minicircuits ADT1-1WT Passband ripple Low Frequency roll-off Will not pass DC High-Speed FDAs offer reduced power and cost as active A/D drivers • Broadband Fully Differential Amplifiers (FDAs) – Easy efficient way to provide DC-coupled interface with gain. • Less power consumption than an RF amp. • Flexible gain options – Gives best performance with differential inputs O S IN + THS770006