ADSP-BF523C_15 Datasheet, PDF (5/36 Pages) Analog Devices – Blackfin Embedded Processor with Codec

ADSP-BF522C/ADSP-BF523C/ADSP-BF524C/ADSP-BF525C/ADSP-BF526C/ADSP-BF527C
MICIN
R_EXT
10kΩ
50kΩ
0dB/20dB/40dB
GAIN BOOST
AVDD
VMID
ADC
OR
SIDETONE
AGND
INTERNAL CIRCUITRY
Figure 3. Microphone Input to ADC
The first gain stage is composed of a low noise operational
amplifier set to an inverting configuration with integrated
50 kΩ feedback and 10 kΩ input resistors. The default micro-
phone input signal gain is 14 dB. An external resistor (R_EXT) can
be connected in series with the MICIN pin to reduce the first-
stage gain of the microphone input signal to as low as 0 dB by
using the following equation:
Microphone Input Gain = 50 kΩ/(10 kΩ + R_EXT)
The second-stage gain of the microphone signal path is derived
from the internal microphone boost circuitry. The available set-
tings are 0 dB, 20 dB, and 40 dB and are controlled by the
MICBOOST (Register R4, Bit D0) and MICBOOST2 (Register
R4, Bit D8) bits. To achieve 20 dB of secondary gain boost, the
programmer can select either MICBOOST or MICBOOST2. To
achieve 40 dB of secondary microphone signal gain, the pro-
grammer must select both MICBOOST and MICBOOST2.
The MUTEMIC bit (Register R4, Bit D1) mutes the microphone
input signal to the ADC.
When using either the line or microphone inputs, the maximum
full-scale input to the ADC is 1.0 V rms when AVDD = 3.3 V.
Do not apply an input voltage larger than full-scale to avoid
overloading the ADC, which causes distortion of sound and
deterioration of audio quality. For best sound quality in both
microphone and line inputs, gain should be carefully configured
so that the ADC receives a signal equal to its full-scale. This
maximizes the signal-to-noise ratio for best total audio quality.
Bypass and Sidetone Paths to Output
The line and microphone inputs can be routed and mixed
directly to the output terminals by programming the SIDET-
ONE (Register R4, Bit D5) and BYPASS (Register R4, Bit D3)
registers. In both modes, the analog input signal is routed
directly to the output terminals and is not digitally converted.
The bypass signal at the output mixer is the same level as the
output of the PGA associated with each line input.
The sidetone signal at the output mixer can be attenuated from
–6 dB to –15 dB in steps of –3 dB by configuring the SIDEATT
(Register R4, Bit D6 and Bit D7) control register bits. The
selected level of attenuation occurs after the initial microphone
signal amplification from the microphone first and second stage
gains.
Line and Headphone Outputs
The DAC outputs, the microphone (the sidetone path), and the
line inputs (the bypass path) are summed at an output mixer
(see Figure 4). This output signal is then applied to both the ste-
reo line outputs and stereo headphone outputs.
LINE
INPUT
BYPASS
MICROPHONE
INPUT
SIDETONE
DAC
OUTPUT
DACSEL
AVDD
LINE OUTPUT
AND
HEADPHONE
OUTPUT
VMID
AGND
INTERNAL CIRCUITRY
Figure 4. Output Signal Chain
The codec has a set of efficient headphone amplifier outputs,
LHPOUT and RHPOUT, that are able to drive 16 Ω or 32 Ω
headphones (shown in Figure 5).
DAC/
SIDETONE/
BYPASS
AVDD
–
VMID
+
RHPOUT
or
LHPOUT
AGND
INTERNAL CIRCUITRY
Figure 5. Headphone Output
Like the line inputs, the LHPOUT and RHPOUT volumes, by
default, are independently adjusted by setting the LHPVOL
(Register R2, Bit D0 to Bit D6) and RHPVOL (Register R3, Bit
D0 to Bit D6) bits of the headphone output control registers.
The headphone outputs can be muted by writing codes less than
0110000 to the LHPVOL and RHPVOL bits.
Rev. A | Page 5 of 36 | March 2010