Amplifier with active-bootstrapped gain-enhancement technique

• Main Authors: SEEVINCK; EVERT, DU PLESSIS; MONUKO
• Format: Patent
• Language: English
• Published: 22.02.2000
• Edition: 7
• Subjects: AMPLIFIERS; BASIC ELECTRONIC CIRCUITRY; ELECTRICITY

In a differential pair (P1, P2) actively loaded with a current mirror (N1, N2), a differential amplifier (A) drives the common terminal (Z) of the current mirror to force a zero voltage difference between the input terminal (X) and the output terminal (Y) of the current mirror. The voltage at the input terminal (X) is actively bootstrapped, via the differential amplifier (A), by the voltage of the output terminal (Y) with high precision. Thus a high voltage gain is obtained. A capacitor (CP) between the input terminal (X) and the control terminal (Z) compensates the local loop formed by the differential amplifier (A) and the input transistor (N1) of the current mirror, and forms a short circuit at high frequencies, thus reducing the active load of the differential pair to a conventional current mirror. For high frequencies the circuit has the same gain and phase properties as the standard non-bootstrapped approach and standard compensating techniques can be applied to the complete amplifier.