adsp-bf527c Analog Devices, Inc., adsp-bf527c Datasheet - Page 8

• Manufacturer Part Number: adsp-bf527c
• Description: Blackfin Embedded Processor
• Manufacturer: Analog Devices, Inc.

ADSP-BF523C/ADSP-BF525C/ADSP-BF527C
Table 1. Line Input Software Control
inputs. These allow a matched interface to the multi-bit over-
sampling ADC and prevent high frequencies from aliasing into
the audio band to degrade performance.
Software control for MICIN is shown in
phone mute only mutes the input to the ADC, which allows the
microphone input signal to pass to the line output in sidetone
mode.
Table 2. Microphone Input Software Control
Register Address Bit Label
000 0000
Left Line In
000 0001
Right Line In
Register
Address
000 0100 0
MICIN
10 K
Bit Label
1
VMID
Figure 5. Microphone Input Internal Circuit
MICBOOST 0
MUTEMIC
4:0 LINVOL[4:0] 10111
7
8
4:0 RINVOL[4:0] 10111
7
8
+
-
50 K
LINMUTE
LRINBOTH
RINMUTE
RLINBOTH
Default Description
1
VMID
Default Description
( 0 dB )
1
0
( 0 dB )
1
0
Microphone Input
Level Boost
1 = Enable Boost
0 = Disable Boost
Microphone Mute to ADC
1 = Enable Mute
0 = Disable Mute
Table
+
-
Left Channel Line Input Volume Control
11111 = +12 dB in 1.5 dB steps down to 00000 =
Left Channel Line Input Mute to ADC
1 = Enable Mute
0 = Disable Mute
Left to Right Channel Line Input Volume and Mute Data Load Control
1 = Enable Simultaneous Load of LINVOL[4:0] and LINMUTE to RINVOL[4:0] and RINMUTE
0 = Disable Simultaneous Load
Right Channel Line Input Volume Control
11111 = +12 dB in 1.5 dB steps down to 00000 =
Right Channel Line Input Mute to ADC
1 = Enable Mute
0 = Disable Mute
Right to Left Channel Line Input Volume and Mute Data Load Control
1 = Enable Simultaneous Load of RINVOL[4:0] and RINMUTE to LINVOL[4:0] and LINMUTE
0 = Disable Simultaneous Load
2. The micro-
Rev. PrC | Page 8 of 44 | June 2008
TO ADC
There are two stages of gain made up of two low noise inverting
operational amplifiers.
The first stage has a nominal gain of G1 = 50 kΩ/10 kΩ = 5. The
gain of the stage can be adjusted by adding an external resistor
(R
tion below can be used to calculate the gain versus R
Gain = 50 kΩ/(R
Or to calculate the value of Rmic to achieve a given gain:
R
For example adding R
(0 dB). For R
= 5x (14 dB).
The internal 50 kΩ and 10 kΩ resistors have a tolerance of 15%.
The second stage has 0 dB gain that can be software configured
to provide a fixed 20 dB of gain for low sensitivity microphones.
The microphone input can therefore be configured with a vari-
able gain of between –6 dB and 14 dB on the first stage, and an
additional fixed 0 dB or 20 dB on the second stage. This allows a
total gain of –6 dB to 34 dB.
To maximize the signal-to-noise ratio, stage 1 and stage 2 gains
should be configured so that the maximum signal that the ADC
receives is equal to the full scale value. The ADC full scale input
is 1.0 V(rms) at AVDD = 3.3 volts. Any voltage greater than full
scale could overload the ADC and cause distortion. The full
scale input tracks directly with AVDD.
The microphone input is biased internally through the opera-
tional amplifier to VMID. Whenever the line inputs are muted
the MICIN input is kept biased to VMID using special anti-
thump circuitry. This reduces audible clicks that may otherwise
be heard when re-activating the input.
mic
mic
= (50 kΩ/Gain)–10 kΩ
) in series with MICIN (see
mic
= 90 kΩ gain = 0.5 (–6 dB) and for R
mic
+ 10 kΩ)
Preliminary Technical Data
–
–
mic
34.5 dB
34.5 dB
= 40 kΩ sets the gain of stage one to 1x
Figure 6 on Page
9). The equa-
mic
mic
.
= 0 gain