TCM29C13A, TCM29C14A, TCM29C16A, TCM29C17A,

TCM129C13A, TC,129C14A, TCM129C16A, TCM129C17A

COMBINED SINGLE-CHIP PCM CODEC AND FILTER

SCTS030E – AUGUST 1989 – REVISED OCTOBER 1996

24

POST OFFICE BOX 655303

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:

R1 and R2 are a gain-setting resistor network with the center tap connected to the GSR input.

A value greater than 10 k

Ω and less than 100 kΩ for R1 + R2 is recommended because of the following:

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.

VOD = A • VA

where A =

1 + (R1/R2)

4 + (R1/R2)

PWRO+

GSR

PWRO–

2

4

3

R1

R2

VOD

VO

RL

PCM IN

TCM29C13A

TCM29C14A

TCM29C16A

TCM29C17A

TCM129C13A

TCM129C14A

TCM129C16A

TCM129C17A

VO–

Digital Milliwatt

Sequence Per

CCITT G. 711

Figure 10. Gain-Setting Configuration