MC145484SD Freescale, MC145484SD Datasheet - Page 5

• Manufacturer Part Number: MC145484SD
• Manufacturer: Freescale
• Type: PCMr

Specifications of MC145484SD

• Number Of Channels: 1
• Gain Control: Adjustable
• Number Of Adc's: 1
• Number Of Dac's: 1
• Adc/dac Resolution: 13b
• Package Type: SSOP
• Sample Rate: 8KSPS
• Number Of Adc Inputs: 1
• Number Of Dac Outputs: 1
• Operating Supply Voltage (max): 5.5V
• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Pin Count: 20
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Not Compliant

ANALOG INTERFACE AND SIGNAL PATH
three–terminal op amp capable of driving a 2 k
op amp has inputs of TI+ (Pin 19) and TI– (Pin 18) and its
output is TG (Pin 17). This op amp is intended to be confi-
gured in an inverting gain circuit. The analog signal may be
applied directly to the TG pin if this transmit op amp is inde-
pendently powered down by connecting the TI+ input to the
V DD power supply. The TG pin becomes high impedance
when the transmit op amp is powered down. The TG pin is
internally connected to a 3–pole anti–aliasing pre–filter. This
pre–filter incorporates a 2–pole Butterworth active low–pass
filter, followed by a single passive pole. This pre–filter is fol-
lowed by a single–ended to differential converter that is
clocked at 512 kHz. All subsequent analog processing uti-
lizes fully–differential circuitry. The next section is a fully–
differential, 5–pole switched–capacitor low–pass filter with
a 3.4 kHz frequency cutoff. After this filter is a 3–pole
switched–capacitor high–pass filter having a cutoff fre-
quency of about 200 Hz. This high–pass stage has a trans-
mission zero at dc that eliminates any dc coming from the
analog input or from accumulated op amp offsets in the pre-
ceding filter stages. The last stage of the high–pass filter is
an autozeroed sample and hold amplifier.
analog converter (DAC) are shared by the transmit and re-
ceive sections. The autozeroed, switched–capacitor
bandgap reference generates precise positive and negative
reference voltages that are virtually independent of tempera-
ture and power supply voltage. A binary–weighted capacitor
array (CDAC) forms the chords of the companding structure,
while a resistor string (RDAC) implements the linear steps
within each chord. The encode process uses the DAC, the
voltage reference, and a frame–by–frame autozeroed
comparator to implement a successive–approximation con-
version algorithm. All of the analog circuitry involved in the
data conversion (the voltage reference, RDAC, CDAC, and
comparator) are implemented with a differential architecture.
sample and hold amplifier, a 5–pole, 3400 Hz switched ca-
pacitor low–pass filter with sinX/X correction, and a 2–pole
active smoothing filter to reduce the spectral components of
the switched capacitor filter. The output of the smoothing fil-
ter is buffered by an amplifier, which is output at the RO– pin.
This output is capable of driving a 2 k
The MC145484 also has a pair of power amplifiers that are
connected in a push–pull configuration. The PI pin is the in-
verting input to the PO– power amplifier. The non–inverting
input is internally tied to the V AG pin. This allows this amplifier
to be used in an inverting gain circuit with two external resis-
MOTOROLA
One bandgap voltage reference generator and digital–to–
The receive section includes the DAC described above, a
The transmit portion of this device includes a low–noise,
FUNCTIONAL DESCRIPTION
Freescale Semiconductor, Inc.
For More Information On This Product,
load to the V AG pin.
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tors. The PO+ amplifier has a gain of minus one, and is in-
ternally connected to the PO– output. This complete power
amplifier circuit is a differential (push–pull) amplifier with ad-
justable gain that is capable of driving a 300
+ 12 dBm. The power amplifier may be powered down inde-
pendently of the rest of the chip by connecting the PI pin to
V DD .
POWER–DOWN
power consumption mode, which makes the device nonfunc-
tional and consumes virtually no power. PDI is the power–
down input pin which, when taken low, powers down the
device. Another way to power the device down is to hold both
the FST and FSR pins low while the BCLKT and MCLK pins
are clocked. When the chip is powered down, the V AG , TG,
RO–, PO+, PO–, and DT outputs are high impedance and
the V AG Ref pin is pulled to the V DD power supply with a non–
linear, high–impedance circuit. To return the chip to the pow-
er–up state, PDI must be high and the FST frame sync pulse
must be present while the BCLKT and MCLK pins are
clocked. The DT output will remain in a high–impedance
state for at least two 8 kHz FST pulses after power–up.
MASTER CLOCK
ture, the MCLK pin is used as the master clock for all analog
signal processing including analog–to–digital conversion,
digital–to–analog conversion, and for transmit and receive fil-
tering functions of this device. The clock frequency applied to
the MCLK pin may be 256 kHz, 512 kHz, 1.536 MHz,
1.544 MHz, 2.048 MHz, 2.56 MHz, or 4.096 MHz. This de-
vice has a prescaler that automatically determines the proper
divide ratio to use for the MCLK input, which achieves the re-
quired 256 kHz internal sequencing clock. The clocking re-
quirements of the MCLK input are independent of the PCM
data transfer mode (i.e., Long Frame Sync, Short Frame
Sync, IDL mode, or GCI mode).
DIGITAL I/O
Table 1 shows the 8–bit data word format for positive and
negative zero and full scale for both companding schemes.
Table 2 shows the series of eight PCM words for both Mu–
Law and A–Law that correspond to a digital milliwatt. The
digital mW is the 1 kHz calibration signal reconstructed by
the DAC that defines the absolute gain or 0 dBm0 Transmis-
sion Level Point (TLP) of the DAC. The timing for the PCM
data transfer is independent of the companding scheme se-
lected. Refer to Figure 2 for a summary and comparison of
the four PCM data interface modes of this device.
There are two methods of putting this device into a low
Since this codec–filter design has a single DAC architec-
The MC145484 is pin selectable for Mu–Law or A–Law.
MC145484
load to
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