| 摘要 |
<p>A low noise amplifier structure based on a Differential Difference Amplifier (DDA1) having a differential output (outp, outn) and two differential pairs of input terminals (N1, P1; N2, P2). The input signal (VIN) is applied to terminals (N2, P1) which belong to different differential pairs. In this way, none of the differential pairs receives a high input signal, and hence none of them cause unacceptable harmonic distortion. The dynamic input range is thus high. The gain of the structure is determined by a resistive circuit (R2a, R2a'; R2b, R2b') coupled to the remaining terminals (N1, P2) of the differential pairs. The common mode of these remaining terminals (N1, P2) is, independently from the output common mode, biased at the input common mode via a common mode feedback circuit (DDA2; GL1, GH1, GH3, R2a, R2a'; GL2, GH2, GH4, R2b, R2b') based on a second differential difference amplifier (DDA2). Some switching elements (GL1, GH1, GH3; GL2, GH2, GH4) allow the gain to be programmed and prevent the common mode feedback circuit from injecting differential noise if the gain is high. The structure is adapted to amplify signals of 1 Vpp with acceptably low distortion. <IMAGE></p> |
