DA7212 Datasheet, PDF (36/129 Pages) Dialog Semiconductor – Ultra-low power stereo codec

DA7212
Ultra-low power stereo codec
Company confidential
13.12 Output mixer
For playback, the output mixer amplifier is enabled using MIXOUT_L_AMP_EN and
MIXOUT_R_AMP_EN. The audio signal can be mixed from all sources, and can be output
simultaneously to both headphones and speakers. The mixing takes place only after asserting the
control MIXOUT_L_MIX_EN and MIXOUT_R_MIX_EN.
The output mixer is configured using register MIXOUT_L_SELECT and MIXOUT_R_SELECT. This
output-mixer control is independent of the input path, so recording of one audio signal while listening
to another signal such as FM Radio or an MP3 file is possible. The playback sound can be mixed
with background signals or with inverted background microphone signals (side tone) to enable a
basic headphone environmental noise reduction, or to compensate for unwanted damping of
environmental sound while listening with sealed headphones. Playback signals coming from the AUX
or microphone input channels can be individually inverted before being mixed out to the left and right
channel (see MIXOUT_L_SELECT and MIXOUT_R_SELECT registers).
A stereo to mono conversion can be implemented by using either the input or the output mixer. This
allows direct feeding of high power speaker amplifiers and other mono devices with the complete
audio content.
13.13 Headphone amplifier
The headphone Class G amplifiers offer 'true ground' technology, which allows cost and space
optimisation by removing the need for bulky headphone-coupling capacitors. This also enhances the
bass performance, which is typically reduced by conventional AC-coupling. In comparison to
alternative approaches like ‘phantom ground’, ‘true ground’ technology generates real
ground-centred output signals, which provide common GND as required for Mini-USB connectors
and CEA 936 A-compliant interfaces. An embedded offset compensation circuit suppresses click and
pop noise during start-up and dynamic supply voltage adjustments.
Integrated short circuit protection enables a ‘resistors free’ connection to a standard audio jack, to
achieve a maximum output power of up to 67 mW per channel (referenced to VDD_A). Headphone
load impedance is typically 16 Ω, but the paths can also be used as volume controlled lineout signals
for external speaker amplifiers and audio devices. The headphone Class G amplifiers are supplied
from the positive VDD_A rail via a capacitive charge pump that generates the negative rail required
for ‘true ground’ mode. For improved power efficiency, the headphone headphone supply voltage
levels are dynamically adjusted between ± VDD_A and ± VDD_A/2 to match the levels of the left and
right headphone signals.
The headphone amplifiers are enabled with controls HP_L_AMP_EN and HP_R_AMP_EN. For
optimum pop and click performance when switching the amplifier On and Off, the headphone
amplifier provides a high impedance mode that can be enabled via HP_L_AMP_OE /
HP_R_AMP_OE.
Balance is controlled by programming the left and right gains separately. The gain of each
headphone channel can be programmed independently in steps of 1.0 dB from +6 dB down to –
57 dB using controls HP_L_AMP_GAIN / HP_R_AMP_GAIN.
Settings such as mute, gain changes at signal zero cross (for smooth volume changes), and the
ramping of gain changes are controlled using the dedicated HP_L_CTRL and HP_R_CTRL registers.
If the ramping is enabled using the control bits HP_L_AMP_RAMP_EN and HP_R_AMP_RAMP_EN,
the rate of the ramping is controlled using GAIN_RAMP_RATE.
For smooth volume changes, the gain update can be synchronised to audio signal zero-crossings
using HP_L_AMP_ZC_EN and HP_R_AMP_ZC_EN. If no zero crossing is detected within
approximately 85 ms, the gain change is applied unconditionally. The left and right channels are
synchronised independently.
Datasheet
Revision 3c
36 of 129
24-Nov-2015
© 2015 Dialog Semiconductor