TLC32044C Datasheet, PDF (6/39 Pages) Texas Instruments – VOICE-BAND ANALOG INTERFACE CIRCUITS

TLC32044C, TLC32044E, TLC32044I, TLC32044M, TLC32045C, TLC32045I
VOICE-BAND ANALOG INTERFACE CIRCUITS
SLAS017F – MARCH 1988 – REVISED MAY 1995
PRINCIPLES OF OPERATION
analog input
Two sets of analog inputs are provided. Normally, the IN + and IN – input set is used; however, the auxiliary input
set, AUX IN + and AUX IN –, can be used if a second input is required. Each input set can be operated in either
differential or single-ended modes, since sufficient common-mode range and rejection are provided. The gain
for the IN +, IN –, AUX IN +, and AUX IN – inputs can be programmed to be either 1, 2, or 4 (see Table 2). Either
input circuit can be selected via software control. It is important to note that a wide dynamic range is assured
by the differential internal analog architecture and by the separate analog and digital voltage supplies and
grounds.
A/D bandpass filter, A/D bandpass filter clocking, and A/D conversion timing
The A/D high-pass filter can be selected or bypassed via software control. The frequency response of this filter
is presented in the following pages. This response results when the switched-capacitor filter clock frequency
is 288 kHz and the A/D sample rate is 8 kHz. Several possible options can be used to attain a 288-kHz
switched-capacitor filter clock. When the filter clock frequency is not 288 kHz, the low-pass filter transfer function
is frequency scaled by the ratio of the actual clock frequency to 288 kHz. The ripple bandwidth and 3-dB
low-frequency roll-off points of the high-pass section are 150 Hz and 100 Hz, respectively. However, the
high-pass section low-frequency roll-off is frequency scaled by the ratio of the A/D sample rate to 8 kHz.
The internal timing configuration and AIC DX data word format sections of this data sheet indicate the many
options for attaining a 288-kHz bandpass switched-capacitor filter clock. These sections indicate that the RX
counter A can be programmed to give a 288-kHz bandpass switched-capacitor filter clock for several master
clock input frequencies.
The A/D conversion rate is then attained by frequency dividing the 288-kHz bandpass switched-capacitor filter
clock with the RX counter B. Unwanted aliasing is prevented because the A/D conversion rate is an integral
submultiple of the bandpass switched-capacitor filter sampling rate, and the two rates are synchronously
locked.
A/D converter performance specifications
Fundamental performance specifications for the A/D converter circuitry are presented in the A/D converter
operating characteristics section of this data sheet. The realization of the A/D converter circuitry with
switched-capacitor techniques provides an inherent sample-and-hold.
analog output
The analog output circuitry is an analog output power amplifier. Both noninverting and inverting amplifier outputs
are brought out. This amplifier can drive transformer hybrids or low-impedance loads directly in either a
differential or single-ended configuration.
D/A low-pass filter, D/A low-pass filter clocking, and D/A conversion timing
The frequency response of this filter is presented in the following pages. This response results when the
low-pass switched-capacitor filter clock frequency is 288 kHz. Like the A/D filter, the transfer function of this filter
is frequency scaled when the clock frequency is not 288 kHz. A continuous-time filter is provided on the output
of the (sin x) / x correction filter to eliminate the periodic sample data signal information, which occurs at multiples
of the 288-kHz switched-capacitor filter clock. The continuous time filter also greatly attenuates any
switched-capacitor clock feedthrough.
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