
Target
Level
Input
Signal
Output
Signal
AGC
Gain
Attack
Time
Decay Time
SLAS548C
– OCTOBER 2008 – REVISED APRIL 2011
Table 3. AGC Parameter Settings (continued)
Control Register
Function
Bit
Left ADC
Right ADC
Debounce time (signal)
Page 0 / register 92
Page 0 / register 100
D(3:0)
Gain applied by AGC
Page 0 / register 93
Page 0 / register 101
D(7:0) (read-only)
AGC noise threshold flag
Page 0 / register 45 (sticky flag),
D(6:5) (read-only)
Page 0 / register 47 (non-sticky flag)
AGC saturation flag
Page 0 / register 36 (sticky flag)
D(5), D(1) (read-only)
ADC saturation flag
Page 0 / register 42 (sticky flag),
D(3:2) (read-only)
Page 0 / register 43 (non-sticky flag)
Figure 32. AGC Characteristics
The TLV320ADC3001 includes three analog audio input pins, which can be configured as one fully-differential
pair and one single-ended input, or as three single-ended audio inputs. These pins connect through series
resistors and switches to the virtual ground terminals of two fully differential operational amplifiers (one per
ADC/PGA channel). By selecting to turn on only one set of switches per operational amplifier at a time, the inputs
can be effectively multiplexed to each ADC PGA channel.
By selecting to turn on multiple sets of switches per operational amplifier at a time, mixing can also be achieved.
Mixing of multiple inputs can easily lead to PGA outputs that exceed the range of the internal operational
amplifiers, resulting in saturation and clipping of the mixed output signal. Whenever mixing is being implemented,
the user should take adequate precautions to avoid such a saturation case from occurring. In general, the mixed
signal should not exceed 2 Vpp (single-ended) or 4 Vpp (differential).
In most mixing applications, there is also a general need to adjust the levels of the individual signals being
mixed. For example, if a soft signal and a large signal are to be mixed and played together, the soft signal
generally should be amplified to a level comparable to the large signal before mixing. In order to accommodate
this need, the TLV320ADC3001 includes input level control on each of the individual inputs before they are
mixed or multiplexed into the ADC PGAs, with programmable attenuation at 0 dB,
–6 dB, or off. Note that this
input level control is not intended to be a volume control, but instead used for coarse level setting. Finer
soft-stepping of the input level is implemented in this device by the ADC PGA.
Copyright
2008–2011, Texas Instruments Incorporated
29