ST70134A

10/22

TX Pre-driver Capability

The pre-driver drives an external line power amplifier which transmits the required power to the line.

TX Filter

The TX filter acts not only to suppress the DMT sidebands but also as smoothing filter on the D/A conver-

tor’s output to suppress the image spectrum. For this reason it must be realized in a continuous time

approach.

ATU-R TX Filter

The purpose of this filter is to remove out-of-band noise of the TX path echoed to the RX path. In order to

meet the transmitter spectral response, an additional filtering must be (digitally) performed. The inte-

grated filter has the following characteristics:

Note: The total TX path (including DAC) group delay distortion is 16

µs (i.e. = 15µs + 1µs of DAC).

Table 10 : TX Pre-driver

TX drive level to the external line

driver for max. AGC setting

1.5 Vpdif

External line driver input impedance:

resistive

capacitive

> 500

Ω

< 30pF

Pre-driver characteristics:

Closed loop gain:

-15dB...0dB with step = 1dB

Output characteristics

Output offset voltage (0dB)

< 10mV

Output noise voltage (0dB)

< 150nVHz-1/2 @ f > 250kHz

< 500nVHz-1/2 @ 34.5kHz < f < 138kHz

0dB

Output common mode voltage:

1.6V < Vcm < 1.7V

Table 11 : Integrated SC Filter Characteristics

Description

Value/Unit

Maximum input level

1Vpd

Maximum output level

1Vpd

Type

4th order chebytchef

Frequency band

138kHz (0% setting see below)

Frequency tuning

-25% -> +25%

Max. in-band ripple

1dB

Matlab Model

Default cut-off frequency @ -3dB

Actual cut-off @ -3dB

SC Frequency selection register

[B,A] = cheby1 (4,0.5,W0,’s’) {ripple = 0.5}

F0 = 151.8kHz

W0 = 2*pi*F0/((17+n)/16)

n = -4,..,3 see (AFE settings, Table 19)

Total TX filter group delay

< 50

µs @ 34.5kHz < f < 138kHz

Total TX filter group delay distortion

< 20

µs @ 34.5kHz < f < 138kHz