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參數資料
| 型號： | TLV320ADC3001IYZHT |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | ADC |
| 英文描述： | 2-CH 16-BIT PROPRIETARY METHOD ADC, SERIAL ACCESS, PBGA16 |
| 封裝： | GREEN, DSBGA-16 |
| 文件頁數： | 20/81頁 |
| 文件大小： | 836K |
| 代理商： | TLV320ADC3001IYZHT |
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SLAS548C
– OCTOBER 2008 – REVISED APRIL 2011
During volume control changes, the soft-stepping feature is used to avoid audible artifacts. The soft-stepping rate
can be set to either 1 or 2 gain steps per sample. Soft-stepping can also be entirely disabled. This soft-stepping
is configured via page 0 / register 81, bits D1
–D0, and is common to soft-stepping control for the analog PGA.
During power-down of an ADC channel, this volume control soft-steps down to
–12 dB before powering down.
Due to the soft-stepping control, soon after changing the volume control setting or powering down the ADC
channel, the actual applied gain may be different from the one programmed through the control register. The
TLV320ADC3001 gives feedback to the user through read-only flags page 0 / register 36, bit D7 for the left
channel and page 0 / register 36, bit D3 for the right channel.
Fine Digital Gain Adjustment
Additionally, the gain in each of the channels is finely adjustable in steps of 0.1 dB. This is useful when trying to
match the gain between channels. By programming page 0 / register 82, the gain can be adjusted from 0 dB
to
–0.4 dB in steps of 0.1 dB. This feature, in combination with the regular digital volume control, allows the gains
through the left and right channels be matched in the range of
–0.5 dB to 0.5 dB with a resolution of 0.1 dB.
AGC
The TLV320ADC3001 includes automatic gain control (AGC) for ADC recording. AGC can be used to maintain a
nominally-constant output level when recording speech. As opposed to manually setting the PGA gain, in the
AGC mode, the circuitry automatically adjusts the PGA gain as the input signal becomes overly loud or weak,
such as when a person speaking into a microphone moves closer to or farther from the microphone. The AGC
algorithm has several programmable parameters, including target gain, attack and decay time constants, noise
threshold, and max PGA applicable, that allow the algorithm to be fine-tuned for any particular application. The
algorithm uses the absolute average of the signal (which is the average of the absolute value of the signal) as a
measure of the nominal amplitude of the output signal. Because the gain can be changed at the sample interval
time, the AGC algorithm operates at the ADC sample rate.
Target level represents the nominal output level at which the AGC attempts to hold the ADC output signal
level. The TLV320ADC3001 allows programming of eight different target levels, which can be programmed
from
–5.5 dB to –24 dB relative to a full-scale signal. Because the TLV320ADC3001 reacts to the signal
absolute average and not to peak levels, it is recommended that the target level be set with enough margin to
avoid clipping at the occurrence of loud sounds.
Attack time determines how quickly the AGC circuitry reduces the PGA gain when the output signal level
exceeds the target level due to increase in input signal level. A wide range of attack-time programmability is
supported in terms of number of samples (i.e., number of ADC sample-frequency clock cycles).
Decay time determines how quickly the PGA gain is increased when the output signal level falls below the
target level due to reduction in input signal level. A wide range of decay time programmability is supported in
terms of number of samples (i.e., number of ADC sample-frequency clock cycles).
Noise threshold is a reference level. If the input speech average value falls below the noise threshold, the
AGC considers it as a silence and hence brings down the gain to 0 dB in steps of 0.5 dB every sample period
and sets the noise-threshold flag. The gain stays at 0 dB unless the input speech signal average rises above
the noise threshold setting. This ensures that noise is not amplified in the absence of speech. Noise threshold
level in the AGC algorithm is programmable from
–30 dB to –90 dB of full-scale. When the AGC noise
threshold is set to
–70 dB, –80 db, or –90 dB, the microphone input max PGA applicable setting must be
greater than or equal to 11.5 dB, 21.5 dB, or 31.5 dB, respectively. This operation includes hysteresis and
debounce to avoid the AGC gain from cycling between high gain and 0 dB when signals are near the noise
threshold level. The noise (or silence) detection feature can be entirely disabled by the user.
Max PGA applicable allows the designer to restrict the maximum gain applied by the AGC. This can be used
for limiting PGA gain in situations where environmental noise is greater than the programmed noise threshold.
Microphone input Max PGA applicable can be programmed from 0 dB to 40 dB in steps of 0.5 dB.
Hysteresis, as the name suggests, determines a window around the noise threshold which must be
exceeded to detect that the recorded signal is indeed either noise or signal. If initially the energy of the
recorded signal is greater than the noise threshold, then the AGC recognizes it as noise only when the
energy of the recorded signal falls below the noise threshold by a value given by hysteresis. Similarly, after
the recorded signal is recognized as noise, for the AGC to recognize it as a signal, its energy must exceed
the noise threshold by a value given by the hysteresis setting. In order to prevent the AGC from jumping
between noise and signal states, (which can happen when the energy of recorded signal is close to the noise
threshold) a non-zero hysteresis value should be chosen. The hysteresis feature can also be disabled.
Debounce time (noise and signal) determines the hysteresis in time domain for noise detection. The AGC
Copyright
2008–2011, Texas Instruments Incorporated
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