TLC32040C, TLC32040I, TLC32041C, TLC32041I

ANALOG INTERFACE CIRCUITS

SLAS014E – SEPTEMBER 1987 – REVISED MAY 1995

7

POST OFFICE BOX 655303

asynchronous versus synchronous operation

If the transmit section of the AIC (low-pass filter and DAC) and receive section (bandpass filter and ADC) are

operated asynchronously, the low-pass and band-pass filter clocks are independently generated from the

master clock signal. Also, the D/A and A/D conversion rates are independently determined. If the transmit and

receive sections are operated synchronously, the low-pass filter clock drives both low-pass and bandpass

filters. In synchronous operation, the A/D conversion timing is derived from, and is equal to, the D/A conversion

timing. (See description of WORD/BYTE in the Terminal Functions table.)

D/A converter performance specifications

Fundamental performance specifications for the D/A converter circuitry are presented in the D/A converter

operating characteristics section of the data sheet. The D/A converter has a sample-and-hold that is realized

with a switched-capacitor ladder.

system frequency response correction

The (sin x) / x correction circuitry is performed in the digital processor software. The system frequency response

can be corrected via DSP software to

±0.1-dB accuracy to band edge of 3000 Hz for all sampling rates. This

correction is accomplished with a first-order digital correction filter, which requires only seven TMS320

instruction cycles. With a 200-ns instruction cycle, seven instructions represent an overhead factor of only 1.1%

and 1.3% for sampling rates of 8 and 9.6 kHz, respectively (see the (sin x) / x correction section for more details).

serial port

The serial port has four possible modes that are described in detail in the Terminal Functions table. These

modes are briefly described below and in the description for WORD/BYTE in the Terminal Functions Table.

the TMS32011 and TMS320C17.

the TMS32020 and the TMS320C25.

the TMS32011 and TMS320C17.

the TMS32020, TMS320C25, or two SN74299 serial-to-parallel shift registers, which can then interface in

parallel to the TMS320C10, TMS32015, to any other digital signal processor, or to external FIFO circuitry.

operation of TLC32040 with internal voltage reference

The internal reference of the TLC32040 eliminates the need for an external voltage reference and provides

overall circuit cost reduction. Thus, the internal reference eases the design task and provides complete control

over the performance of this integrated circuit. The internal reference is brought out to a terminal and is available

to the designer. To keep the amount of noise on the reference signal to a minimum, an external capacitor may

be connected between REF and ANLG GND.

operation of TLC32040 or TLC32041 with external voltage reference

REF can be driven from an external reference circuit if so desired. This external circuit must be capable of

supplying 250

µA and must be adequately protected from noise such as crosstalk from the analog input.