Advanced Information
WM8753L
POWER CONTROL
The design of the WM8753L has given much attention to power consumption without compromising
performance. It operates at very low voltages, and includes the ability to power off any unused parts
of the circuitry under software control, and includes standby and power off modes.
OPERATION SCENARIOS
Flexibility in the design of the WM8753L allows for a wide range of operational scenarios, some of
which are proposed below:
Telephony with MP3 playback: The voice codec may be used as standard voice codec, and the
stereo DAC used for MP3 type playback. The user may choose to transmit the mono version of the
MP3 playback to the Tx side of the phone conversation as required. Recording of the phone
conversation would then require to be supported in the digital domain, after the voice codec. (digital
Tx and Rx sides of the conversation would need to be digitally summed as required).
Telephony with recording: In many smart-phone applications the voice codec for voice conversion will
be included in the cellphone base-band chipset. In such cases the analog (often differential) mic input
and speaker outputs from this voice codec will be routed to the WM8753L line or mic inputs, and
mono outputs. The WM8753L will then provide the buffers to connect to the system transducers
(speakers, mics, headphones etc.) and also the stereo hi-fi DAC and mixers to allow MP3 type
playback. The ADC may then be used for recording the phone conversation, both Tx and Rx parts,
and the extra DAC might be used for generation of confirmation tones or ringtones as required.
Bluetooth Hi-Fi stereo headset; In Bluetooth headsets a mono PCM codec is required for the
standard telephony quality voice channel. But for the support of compressed hi-fi quality stereo, a hi-fi
quality stereo DAC is required. In this case WM8753L can supply both these needs. The BTL speaker
driver could be recommitted as either stereo headphone driver, or stereo speaker driver, and perhaps
the other headphone output re-used as stereo line output.
Analog FM tuner support: An analog stereo FM tuner might be connected to the Line inputs of
WM8753, and the stereo signal listened to via headphones, or transmitted over the ‘phone.
INPUT SIGNAL PATH
The WM8753L has a combination of analogue inputs, microphone preamps, mixers and switches
allowing flexibility in the configuration of the input to left and right ADCs and to analogue bypass
paths into the Left, Right and Mono output Mixers. The input to the ADC may be routed through a
PGA whose gain is controlled either by the user or by the on-chip ALC function (see Automatic Level
Control). The ADCs may be powered off independently and a single ADC may be used for left and
right ADC input mono mixing.
SIGNAL INPUTS
The WM8753L has three sets of high impedance, low capacitance AC coupled differential inputs as
well as two high impedance, low capacitance AC coupled mono line inputs. Two of the differential
inputs (MICIN1/MICIN1N and MICIN2/MICIN2N) have a microphone pre-amp and selectable gain of
+12dB to +30dB in 6dB steps. RXN and RXP are a differential line input and can also be configured
as a stereo to mono mix input. In addition there are two mono LINE inputs (LINE1 and LINE2) which
can be used as a single stereo input.
The LINE1 and LINE2 inputs may be configured as a differential input or a stereo to mono mix using
the Line input mixer under the control of register bits LMSEL. The LMSEL bits also allow either one
of the inputs to be enabled and the other disabled. The Line mixer output may then be routed to the
ALC mixer by setting LINEALC and/or to the output Mono mixer via the bypass path. The Line mixer
has -6dB of gain so that a 0dB signal on LINE1 and LINE2 will sum to give a 0dB signal at the mixer
output.
There is an analogue input to analogue output bypass path into the Left, Right and Mono output
mixers. The Left bypass path may be selected to be either the output of the RX mixer or the LINE1
input under the control of LM. The Right bypass path may be selected to be either the output of the
RX mixer or the LINE2 input under the control of RM. The Mono bypass path may be selected to be
either the output of the Line mixer or the RX mixer under the control of MM.
AI Rev 3.1 June 2004
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
