DC level control for an electronic telephone line card
US5583934A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Mar 3, 1995 |
| Grant date | Dec 10, 1996 |
| Priority date | — |
| Expiry date | Mar 3, 2015 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M3/005
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
DC level control for an electronic telephone line card which filters the DC component from the input audio signal, determines the gain setting of the transmit path, develops a DC adjust voltage opposite to that of the DC shift component and subtracts the DC adjust voltage to the input voltage to cancel the DC shift component. A quantized, discontinuous feedback path is implemented to respond only to DC shifts so the AC operation remains substantially unaffected. Such discontinuous feedback eliminates stability and impedance matching problems introduced with continuous feedback solutions. A DC control circuit according to the present invention includes a low pass filter for detecting DC shifts, a quantizer for asserting an incremental signal, a threshold detector for activating adjustment functions, and an accumulator for developing the DC adjust voltage by incremental steps. A long term low pass filter and reset circuit resets the accumulator to cancel residual DC adjust voltages which might otherwise reduce the dynamic range of the telephone line transmit path.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.