TCM29C13A Datasheet, PDF (24/25 Pages) Texas Instruments – COMBINED SINGLE-CHIP PCM CODEC AND FILTER

TCM29C13A, TCM29C14A, TCM29C16A, TCM29C17A,
TCM129C13A, TC,129C14A, TCM129C16A, TCM129C17A
COMBINED SINGLE-CHIP PCM CODEC AND FILTER
SCTS030E – AUGUST 1989 – REVISED OCTOBER 1996
PRINCIPLES OF OPERATION
receive output power amplifiers
A balanced-output amplifier allows maximum flexibility in output configuration. Either of the two outputs can be
used single ended (i.e., referenced to ANLG GND) to drive single-ended loads. Alternatively, the differential
output directly drives a bridged load. The output stage is capable of driving loads as low as 300-Ω single-ended
to a level of 12 dBm or 600 Ω differentially to a level of 15 dBm.
The receive channel transmission level may be adjusted between specified limits by manipulation of GSR. GSR
is internally connected to an analog gain-setting network. When GSR is connected to PWRO –, the receive level
is maximum. When GSR is connected to PWRO+, the level is minimum. The output transmission level is
adjusted between 0 and –12 dB as GSR is adjusted (with an adjustable resistor) between PWRO+ and PWRO –.
Transmission levels are specified relative to the receive channel output under digital milliwatt conditions
(i.e., when the digital input at PCM IN is the eight-code sequence specified in CCITT recommendation G.711).
APPLICATION INFORMATION
output gain-set design considerations (see Figure 9)
PWRO+ and PWRO – are low-impedance complementary outputs. The voltages at the nodes are:
V_{O +} at PWRO +
V_{O –} at PWRO –
V_O = V_{O +} – V_{O –} (total differential response)
R1 and R2 are a gain-setting resistor network with the center tap connected to the GSR input.
A value greater than 10 kΩ and less than 100 kΩ for R1 + R2 is recommended because of the following:
The parallel combination of R1 + R2 and R_L sets the total loading.
The total capacitance at the GSR input and the parallel combination of R1 and R2 define a time constant that
has to be minimized to avoid inaccuracies.
V_A represents the maximum available digital milliwatt output response (V_A = 3.006 Vrms).
VOD = A • VA
1 + (R1/R2)
where A =
4 + (R1/R2)
VO
RL
R1
VOD
R2
VO _–
2
PWRO+
4
GSR
TCM29C13A
TCM29C14A
TCM29C16A
TCM29C17A
TCM129C13A
TCM129C14A
TCM129C16A
TCM129C17A
3
PWRO–
PCM IN
Figure 10. Gain-Setting Configuration
Digital Milliwatt
Sequence Per
CCITT G. 711
24
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