MAS9090B Micro Analog Systems, MAS9090B Datasheet - Page 17

• Manufacturer Part Number: MAS9090B
• Description: Low Voltage 14-bit Linear Codec
• Manufacturer: Micro Analog Systems

Analog front end provides three identical differential
inputs
connection of microphones or auxiliary audio
circuits. Desired input signal is selected with bits VS
and TE (6 and 7) of register CR4 and forwarded to a
low noise preamplifier.
Preamplifier has 16.1 dB gain and its output is fed
to the programmable gain amplifier which provides
an additional gain from 0 to 22.5 dB in 1.5 dB steps.
Gain is controlled with bits 4-7 of register CR5.
An active RC anti alias filter is used to prevent
signal folding during the sampling. Accurate analog
to digital conversion is done by using a sigma-delta
modulator followed by a decimation filter.
Digital multiplexer (bit DE (0) in CR 7) is used to
select the input of a digital bandpass filter (300-
3400 Hz). The input can be taken from the output of
the decimator or from an internal ring/tone
generator. The bandpass filter output contains hard
clipping saturation logic for signals exceeding
overload level (+3.14 dB). Highpass part of the
bandpass filter can be bypassed with bit HPT of
register CR10.
Output data can be compressed by using CCITT A-
law or 255-law coding. The compression code is
selected with bits CM (5), MA (4) and IA (3) of
register CR0.
Received signal is transferred into RX register in 8
bit encoded format or in 16 bit linear format. The
data is expanded by using A-law or
encoding according to CCITT A and 255 laws. The
expansion code is selected with bits CM (5), MA (4)
and IA (3) of register CR0. Signal is then passed
through a bandpass filter (bandpass 300-3400 Hz).
The high pass section of the filter can be bypassed
with bit HPR of register CR4.
The input signal of RX gain3 is controlled with bits
SI (5), RTE (2) and SE (0) of register CR4. Bit SI
activates the transmit side tone signal, bit RTE
activates the ring/tone generator and bit SE
activates the received signal to be summed to the
gain input. RX gain3 can be programmed with bits
4-7 of register CR6 from 0 dB to -30 dB with -2dB
steps. It contains also hard-clipping saturation logic.
After gain adjustment the signal is fed to a digital
sigma-delta modulator followed by a switched
capacitor (SC) reconstruction filter and a continuous
time smoothing filter. Filtered analog signal can be
directed to a speaker amplifier (SP1) or to an extra
analog output amplifier (SP2) with bits OE1 (4) and
OE2 (3) of register CR4. Gains can be set with
register CR6 in the range of 0 to -30 dB in -2 dB
steps.
(MIC1,
MIC2,
MIC3)
for
-law signal
capacitive
Differential analog outputs (SP1, SP2) are capable
of directly driving output load of 30
level up to 66mW. Also ceramic receivers up to
50nF can be used. Power up transient noise
suppression is used in both outputs.
Ring/tone generator is able to generate one or two
sinewave or squarewave frequencies (including
DTMF tones) to the transmit (TX) receive (RX) or
buzzer paths. Generated frequencies can be
programmed with registers CR8 and CR9. One of
the three frequency ranges can be selected with bits
DFT and HFT of register CR10. Output signal level
of the tone generator can be selected from 0 to -27
dB with -3dB steps with bits 4-7 of register CR7.
Single ended BZ output is used to drive a buzzer by
using an external bipolar transistor with pulse width
modulated (PWM) squarewave signal f1 (CR8).
This PWM signal can also be amplitude modulated
with signal f2 (CR9). Maximum load for BZ is 5 k
and 50pF. Implementation of tone generator is fully
digital. Therefore no amplitude or
response
temperature, power supply or from unit to unit exist.
variations
(at
TX
March 20, 1998
output)
DA9090B.002
with power
frequency
over
17