High impedance bias circuit for ac signal amplifiers

G - Physics – 05 – F

Patent

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Details

G05F 1/10 (2006.01) G05F 1/573 (2006.01) G05F 3/20 (2006.01) G05F 3/24 (2006.01) G05F 3/26 (2006.01)

Patent

CA 2270938

The present invention discloses an integrated constant bias voltage generator using only active device to simulate a high impedance node, as seen from a capacitively coupled input signal VIN. A reference current source (56) and an active nonlinear device (51), such as a MOS transistor (91), are coupled in series between VCC and ground with the drain electrode X of the nonlinear device (51) being the constant bias voltage output VBIAS. An input signal VIN capacitively coupled to said drain electrode X introduces an error current .DELTA.i monitored by a current monitoring means (58). A feedback means (57) responsive to the current monitoring means (58) modulates the control input Z of the nonlinear device (51) to select an IXY vs. VXZ characteristic current- voltage curve that maintains the VXZ voltage of the nonlinear device (51) at its current level in spite of changes in its IXY current due to the error current .DELTA.i. The feedback means (57) also compensates for voltage fluctuations in VCC.

La présente invention concerne un générateur de tension de polarisation constante intégré qui utilise uniquement un dispositif actif pour stimuler un noeud à haute impédance, comme indiqué par un signal d'entrée V¿IN? à couplage capacitif. Une source de courant de référence (56) et un dispositif non linéaire actif (51), tel qu'un transistor MOS (91), sont couplés en séries entre la tension de courant continu et la masse, l'électrode de drain X du dispositif non linéaire (51) étant la sortie de tension de polarisation constante V¿BIAS?. Un signal d'entrée V¿IN? relié par couplage capacitif à ladite électrode de drain X apporte un courant d'erreur (.DELTA.i) surveillé par un moyen de surveillance du courant (58). Un moyen de rétroaction (57) répondant au moyen de surveillance du courant (58) module l'entrée de commande (Z) du dispositif non linéaire (51) pour sélectionner une courbe de courant-tension caractéristique I¿XY? opposé à V¿XZ? qui maintient la tension V¿XZ? du dispositif non linéaire (51) à son niveau courant malgré des changements de son courant I¿XY? imputable au courant d'erreur (.DELTA.i). Le moyen de rétroaction (57) compense également les variations de tension dans la tension de courant continu.

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