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AD20MSP410-EB03 View Datasheet(PDF) - Analog Devices

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Description
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AD20MSP410-EB03
ADI
Analog Devices ADI
AD20MSP410-EB03 Datasheet PDF : 8 Pages
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AD20msp410
decision confidence bits supplied by the equalizer. Once these
decoding functions are complete, digitized voice data is trans-
ferred to the ASP through a parallel port. Error control mecha-
nisms are used to ensure adequate bad frame indication.
Speech Decoding (ASP)
Encoded speech data is transferred at 20 ms intervals from the
PLP to the ASP in blocks of 260 bits plus the Bad Frame
Indicator (BFI). The speech decoder supports a Comfort Noise
Insertion (CNI) function that inserts a predefined silence
descriptor into the decoding process. The ASP also implements
control of talker side-tone and short term echo cancellation.
The resulting data, at 104 kb/s, is transferred to the BBC
through a dedicated serial path.
Voice Digital-to-Analog Conversion
The Voice DAC function of the BBC uses a sigma-delta con-
verter to convert and noise shape the signal. The 13-bit linear
values are converted to the analog domain and filtered to avoid
any images. The resulting differential signals can be controlled
in volume and drive directly a small earpiece as well as a
separate auxiliary output.
AUXILIARY SYSTEM FUNCTIONS
The ASP, the PLP and the BBC perform a number of auxiliary
functions which are essential to build a complete mobile radio.
A general radio section constitutes the three functions of
transmitter, receiver and synthesizer. Figure 2 shows how the
baseband chipset interfaces to a typical radio architecture. The
transmitter is fed with baseband analog I and Q signals from the
BBC and upconverted to 900 MHz for GSM applications and
1800 MHz for PCN applications.
A dedicated power amplifier increases the RF-signal to the
required level. The receiver amplifies the antenna signal, down-
converts it to an intermediate frequency (IF) and amplifies it
there again. After second conversion to baseband, the I and Q
components of the signal are fed into the BBC.
The BBC, ASP and PLP provide three auxiliary functions for
interfacing to the radio subsystem. These auxiliary functions
include AGC, AFC and Power Ramping.
Power Ramp Envelope (BBC)
To meet the spectral and time-domain specifications of the
transmitted output signal, the burst has to follow a specified
power envelope. The envelope for the power profile originates in
the PLP as a set of coefficients, down-loaded and stored in the
BBC. This envelope profile is sent to one of the auxiliary DACs
on the BBC with each burst. The analog output is fed into the
RF power amplifier, controlling the power profile and absolute
level of the transmitted data.
Automatic Gain Control (AGC)
The mobile radio has to cope with a wide range of input signal
levels. The major part of the overall gain is provided in the IF
amplifier. The incoming signal level is analyzed in the ASP and
the PLP and a digital gain control signal is sent to the BBC. A
10-bit auxiliary DAC generates the appropriate analog control
signal for the IF amplifier. Additionally gain control can be
implemented by using two output flags of the ASP.
BASEBAND/AUXILIARY SECTION OF AD7015
I
TX DAC
BURST
GSMSK
STORE
MODULATOR
Q
TX DAC
BASEBAND
SERIAL
INTERFACE
DIDGDIIGGTIAITTLAALFLIFRFIIRFRIFLFITILLETTREERR
I
RX DAC
DDIIGGIITTAALL FFIIRR FFIILLTTEERR
Q
RX DAC
PA
IF
AUXILIARY
SERIAL
INTERFACE
8-BIT DAC
10-BIT DAC
10-BIT DAC
AGC
AFC
13 MHz VCTCXO
RAMPING RAM
10-BIT DAC
RAMP CONTROL
ASP
FLAGS
PLP
SYNTHESIZER
CONTROL SIGNALS
AGC
LOCK
PAERROR
13 MHz VCTCXO
Figure 2. Control of RF Section
REV. 0
–3–
 

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