DIGITAL/ANALOGUE CONVERSION

摘要

The application relates to digital to analogue conversion circuits having dynamic gain control. A digital variable gain element (102) may apply gain to an input digital signal (DIN) upstream of a DAC (101) to make better use of the input range of the DAC and an analogue variable gain element (103) applies a compensating analogue gain. Again controller (201) has a gain allocation module (204) for controlling the allocation of gain between said digital and analogue variable gain elements in response to changes in a signal level of the input digital audio signal. In the present invention the gain allocation module is operable in first and second modes of operation where the response to reductions in signal level is slower in the first mode than in the second mode of operation. A low-level detector (202) monitors the input digital audio signal so as to detect a low-level part of the signal and the gain controller changes from the first mode to the second mode following detection of a low-level part of the input digital audio signal. The response of the gain allocation module in the second mode is preferably fast enough such that the digital gain can be changed to a target setting suitable for the low-level part of the signal before it is received at the digital gain element.

主权项

1. A digital to analogue conversion circuit comprising:
a digital input for receiving an input digital audio signal; an analogue output for outputting an analogue version of the input digital audio signal; a digital-to-analogue converter located in a signal path between the digital input and analogue output and having a DAC input; a digital variable gain element configured to apply a digital gain in a segment of said signal path between the digital input and the DAC input; an analogue variable gain element configured to apply an analogue gain in a segment of said signal path between the DAC input and the analogue output; and a gain controller comprising:
a gain allocation module configured to control the allocation of gain between said digital and analogue variable gain elements in response to changes in a signal level of the input digital audio signal;wherein said gain allocation module is operable in first and second modes of operation wherein the response of the gain allocation module to reductions in said signal level of the input digital signal is slower in the first mode than in the second mode of operation; anda low-level detector configured to monitor the input digital audio signal at the digital input so as to detect a low-level part of the signal; wherein the gain controller is configured to change said gain allocation module from said first mode of operation to said second mode of operation following detection by said low-level detector of a low-level part of the input digital audio signal.