GENERATING A TAIL CURRENT FOR A DIFFERENTIAL TRANSISTOR PAIR USING A CAPACITIVE DEVICE TO PROJECT A CURRENT FLOWING THROUGH A CURRENT SOURCE DEVICE ONTO A NODE HAVING A DIFFERENT VOLTAGE THAN THE CURRENT SOURCE DEVICE
US6462584B1 · kind B1 · utility
Assignee
Inventor
Key dates
| Filing date | Feb 11, 2000 |
| Grant date | Oct 8, 2002 |
| Priority date | — |
| Expiry date | Feb 11, 2020 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH10B12/488
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
A current tail circuit and method for a differential transistor pair affords the capability of sensing an input differential signal having a low common mode voltage when using, for example, an NMOS differential transistor pair. A current source device and a capacitor may be employed to provide at the common node of the differential transistor pair what appears to be a constant current source connected to a “negative voltage.” In one embodiment particularly useful when using an NMOS differential pair, one terminal of a capacitor is precharged to VDD and the other terminal is precharged to VSS (i.e., ground). When the amplifier needs to sense its differential input signal, a control signal turns off precharge transistors and couples the capacitor terminal previously precharged to VSS to the common-source node of a differential transistor pair. The capacitor terminal previously precharged to VDD is driven toward VSS, preferably with a controlled current source, which couples the common-source node of the differential pair from VSS toward a voltage below VSS. As soon as the common-source node voltage is low enough for at least one side of the differential pair to conduct a …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.