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Freescale Semiconductor, Inc.
SEMICONDUCTOR TECHNICAL DATA
Order this document
by MC145483/D
3 V 13-Bit Linear PCM
Codec-Filter
The MC145483 is a 13–bit linear PCM Codec–Filter with 2s complement data
format, and is offered in 20–pin SOG, SSOP, and TSSOP packages, and a
32–pin QFN package. This device performs the voice digitization and
reconstruction as well as the band limiting and smoothing required for the voice
coding in digital communication systems. This device is designed to operate in
both synchronous and asynchronous applications and contains an on–chip
precision reference voltage.
This device has an input operational amplifier whose output is the input to the
encoder section. The encoder section immediately low–pass filters the analog
signal with an active R–C filter to eliminate very high frequency noise from being
modulated down to the passband by the switched capacitor filter. From the
active R–C filter, the analog signal is converted to a differential signal. From this
point, all analog signal processing is done differentially. This allows processing
of an analog signal that is twice the amplitude allowed by a single–ended
design, which reduces the significance of noise to both the inverted and
non–inverted signal paths. Another advantage of this differential design is that
noise injected via the power supplies is a common–mode signal that is
cancelled when the inverted and non–inverted signals are recombined. This
dramatically improves the power supply rejection ratio.
After the differential converter, a differential switched capacitor filter band–
passes the analog signal from 200 Hz to 3400 Hz before the signal is digitized
by the differential 13–bit linear A/D converter. The digital output is 2s
complement format.
The decoder digital input accepts 2s complement data and reconstructs it
using a differential 13–bit linear D/A converter. The output of the D/A is
low–pass filtered at 3400 Hz and sinX/X compensated by a differential switched
capacitor filter. The signal is then filtered by an active R–C filter to eliminate the
out–of–band energy of the switched capacitor filter.
The MC145483 PCM Codec–Filter has a high–impedance VAG reference pin
which allows for decoupling of the internal circuitry that generates the
mid–supply VAG reference voltage to the VSS power supply ground. This
reduces clock noise on the analog circuitry when external analog signals are
referenced to the power supply ground.
The MC145483 13–bit linear PCM Codec–Filter accepts both Short Frame
Sync and Long Frame Sync clock formats, and utilizes CMOS due to its reliable
low–power performance and proven capability for complex analog/digital VLSI
functions.
•
•
•
•
•
•
•
•
Single 3 V Power Supply
13–Bit Linear ADC/DAC Conversions with 2s Complement Data Format
Typical Power Dissipation of 8 mW, Power–Down of 0.01 mW
Fully–Differential Analog Circuit Design for Lowest Noise
Transmit Band–Pass and Receive Low–Pass Filters On–Chip
Transmit High–Pass Filter May be Bypassed by Pin Selection
Active R–C Pre–Filtering and Post–Filtering
On–Chip Precision Reference Voltage of 0.886 V for a – 5 dBm TLP
@ 600
Ω
•
3–Terminal Input Op Amp Can be Used, or a 2–Channel Input Multiplexer
•
Receive Gain Control from 0 dB to – 21 dB in 3 dB Steps in Synchronous
Operation
•
Push–Pull 300–Ω Power Drivers with External Gain Adjust
20
MC145483
DW SUFFIX
SOG PACKAGE
CASE 751D
1
20
1
SD SUFFIX
SSOP
CASE 940C
Freescale Semiconductor, Inc...
20
1
DT SUFFIX
TSSOP
CASE 948E
1
32
FC SUFFIX
QFN
CASE 1311
ORDERING INFORMATION
MC145483DW
MC145483SD
MC145483DT
MC145483FC
SOG Package
SSOP
TSSOP
QFN
REV 3
4/2003
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MC145483
Freescale Semiconductor, Inc.
PIN ASSIGNMENTS
20-PIN
SOG, SSOP, and TSSOP
V
AG
Ref
RO–
PI
PO–
PO+
V
DD
FSR
DR
BCLKR
PDI
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
V
AG
TI+
TI–
TG
HB
V
SS
FST
DT
BCLKT
MCLK
32-PIN
QFN
NC
NC
RO–
V
AG
Ref
V
AG
TI+
NC
NC
NC
PI
PO–
NC
PO+
V
DD
FSR
NC
1
2
3
4
5
6
7
8
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
NC
DR
BCLKR
PDI
MCLK
BCLKT
DT
NC
9
10
11
12
13
14
15
16
NC
TI–
TG
HB
NC
V
SS
FST
NC
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2
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RECEIVE
SHIFT
REGISTER
RO –
PI
–
+
SHARED
DAC
PO +
VDD
VSS
VAG Ref
–1
VDD
R*
0.886 V
REF
1
VSS
R*
SEQUENCE
AND
CONTROL
FSR
BCLKR
PDI
MCLK
BCLKT
FST
FREQ
DAC
DR
PO –
Freescale Semiconductor, Inc...
VAG
TG
TI –
TI +
–
+
FREQ
HB
ADC
TRANSMIT
SHIFT
REGISTER
DT
Figure 1. MC145483 13–Bit Linear PCM Codec–Filter Block Diagram
DEVICE DESCRIPTION
A PCM Codec–Filter is used for digitizing and reconstruct-
ing the human voice. These devices are used primarily for
the telephone network to facilitate voice switching and trans-
mission. Once the voice is digitized, it may be switched by
digital switching methods or transmitted long distance (T1,
microwave, satellites, etc.) without degradation. The name
codec is an acronym from ‘‘COder’’ for the analog–to–digital
converter (ADC) used to digitize voice, and ‘‘DECoder’’ for
the digital–to–analog converter (DAC) used for reconstruct-
ing voice. A codec is a single device that does both the ADC
and DAC conversions.
To digitize intelligible voice requires a signal–to–distortion
ratio of about 30 dB over a dynamic range of about 40 dB.
This may be accomplished with a linear 13–bit ADC and
DAC. The MC145483 satisfies these requirements and may
be used as the analog front–end for voice coders using DSP
technology to further compress the digital data stream.
In a sampling environment, Nyquist theory says that to
properly sample a continuous signal, it must be sampled at a
frequency higher than twice the signal’s highest frequency
component. Voice contains spectral energy above 3 kHz, but
its absence is not detrimental to intelligibility. To reduce the
digital data rate, which is proportional to the sampling rate, a
sample rate of 8 kHz was adopted, consistent with a band-
width of 3 kHz. This sampling requires a low–pass filter to
limit the high frequency energy above 3 kHz from distorting
the in–band signal. The telephone line is also subject to
50/60 Hz power line coupling, which must be attenuated
from the signal by a high–pass filter before the analog–to–
digital converter. The MC145483 includes a high–pass filter
for compatibility with existing telephone applications, but it
may be removed from the analog input signal path by the
high–pass bypass pin.
The digital–to–analog conversion process reconstructs a
staircase version of the desired in–band signal, which has
spectral images of the in–band signal modulated about the
sample frequency and its harmonics. These spectral images
are called aliasing components, which need to be attenuated
to obtain the desired signal. The low–pass filter used to at-
tenuate these aliasing components is typically called a re-
construction or smoothing filter.
The MC145483 PCM Codec–Filter has the codec, both
presampling and reconstruction filters, and a precision volt-
age reference on–chip.
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MC145483
Freescale Semiconductor, Inc.
PIN DESCRIPTIONS
POWER SUPPLY
VDD
Positive Power Supply (Pin 6)
This is the most positive power supply and is typically con-
nected to + 3 V. This pin should be decoupled to VSS with a
0.1
µF
ceramic capacitor.
VSS
Negative Power Supply (Pin 15)
This is the most negative power supply and is typically
connected to 0 V.
VAG
Analog Ground Output (Pin 20)
when a logic 1 is applied to this pin. The device goes through
a power–up sequence when this pin is taken to a logic 1
state, which prevents the DT PCM output from going low im-
pedance for at least two FST cycles. The VAG and VAG Ref
circuits and the signal processing filters must settle out be-
fore the DT PCM output or the RO– receive analog output
will represent a valid analog signal.
ANALOG INTERFACE
TI+
Transmit Analog Input (Non–Inverting) (Pin 19)
This is the non–inverting input of the transmit input gain
setting operational amplifier. This pin accommodates a differ-
ential to single–ended circuit for the input gain setting op
amp. This allows input signals that are referenced to the V SS
pin to be level shifted to the VAG pin with minimum noise.
This pin may be connected to the VAG pin for an inverting
amplifier configuration if the input signal is already refer-
enced to the VAG pin. The common mode range of the TI+
and TI– pins is from 1.2 V, to V DD minus 1.2 V. This is an FET
gate input.
The TI+ pin also serves as a digital input control for the
transmit input multiplexer. Connecting the TI+ pin to V DD will
place this amplifier’s output (TG) into a high–impedance
state, and selects the TG pin to serve as a high–impedance
input to the transmit filter. Connecting the TI+ pin to VSS will
also place this amplifier’s output (TG) into a high–impedance
state, and selects the TI– pin to serve as a high–impedance
input to the transmit filter.
TI–
Transmit Analog Input (Inverting) (Pin 18)
This is the inverting input of the transmit gain setting op-
erational amplifier. Gain setting resistors are usually con-
nected from this pin to TG and from this pin to the analog
signal source. The common mode range of the TI+ and TI–
pins is from 1.2 V to VDD – 1.2 V. This is an FET gate input.
The TI– pin also serves as one of the transmit input mulit-
plexer pins when the TI+ pin is connected to VSS. When TI+
is connected to VDD, this pin is ignored. See the pin descrip-
tions for the TI+ and the TG pins for more information.
TG
Transmit Gain (Pin 17)
This is the output of the transmit gain setting operational
amplifier and the input to the transmit band–pass filter. This
op amp is capable of driving a 2 kΩ load. Connecting the TI+
pin to VDD will place the TG pin into a high–impedance state,
and selects the TG pin to serve as a high–impedance input to
the transmit filter. All signals at this pin are referenced to the
VAG pin. When TI+ is connected to VSS, this pin is ignored.
See the pin descriptions for TI+ and TI– pins for more in-
formation. This pin is high impedance when the device is in
the powered–down mode.
RO–
Receive Analog Output (Inverting) (Pin 2)
This is the inverting output of the receive smoothing filter
from the digital–to–analog converter. This output is capable
of driving a 2 kΩ load to 0.886 V peak referenced to the VAG
pin. If the device is operated half–channel with the FST pin
clocking and FSR pin held low, the receive filter input will be
Freescale Semiconductor, Inc...
This output pin provides a mid–supply analog ground. This
pin should be decoupled to VSS with a 0.01
µF
ceramic ca-
pacitor. All analog signal processing within this device is ref-
erenced to this pin. If the audio signals to be processed are
referenced to V SS, then special precautions must be utilized
to avoid noise between V SS and the VAG pin. Refer to the ap-
plications information in this document for more information.
The VAG pin becomes high impedance when this device is in
the powered–down mode.
VAG Ref
Analog Ground Reference Bypass (Pin 1)
This pin is used to capacitively bypass the on–chip circuit-
ry that generates the mid–supply voltage for the VAG output
pin. This pin should be bypassed to VSS with a 0.1
µF
ceram-
ic capacitor using short, low inductance traces. The VAG Ref
pin is only used for generating the reference voltage for the
VAG pin. Nothing is to be connected to this pin in addition to
the bypass capacitor. All analog signal processing within this
device is referenced to the VAG pin. If the audio signals to be
processed are referenced to VSS, then special precautions
must be utilized to avoid noise between VSS and the VAG pin.
Refer to the applications information in this document for
more information. When this device is in the powered–down
mode, the VAG Ref pin is pulled to the VDD power supply with
a non–linear, high–impedance circuit.
CONTROL
HB
Transmit High–Pass Filter Bypass (Pin 16)
This pin selects whether the transmit high–pass filter will
be used or bypassed, which allows frequencies below
200 Hz to appear at the input of the ADC to be digitized. This
high–pass filter is a third order filter for attenuating power line
frequencies, typically 50/60 Hz. A logic low selects this filter.
A logic high deselects or bypasses this filter. When the filter
is bypassed, the transmit frequency response extends down
to dc.
PDI
Power–Down Input (Pin 10)
This pin puts the device into a low power dissipation mode
when a logic 0 is applied. When this device is powered down,
all of the clocks are gated off and all bias currents are turned
off, which causes RO–, PO–, PO+, TG, VAG, and DT to be-
come high impedance. The device will operate normally
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