參數(shù)資料
型號(hào): TLC32046M
廠商: Texas Instruments, Inc.
英文描述: Wide-Band Analog Interface Circuit
中文描述: 寬帶模擬接口電路
文件頁數(shù): 16/57頁
文件大小: 297K
代理商: TLC32046M
2–2
2.1
All the internal timing of the AIC is derived from the high-frequency clock signal that drives the master clock
input. The shift clock signal, which strobes the serial port data between the AIC and DSP, is derived by
dividing the master clock input signal frequency by four.
The TX(A) counter and the TX(B) counter, which are driven by the master clock signal, determine the D/A
conversion timing. Similarly, the RX(A) counter and the RX(B) counter determine the A/D conversion timing.
In order for the low-pass switched-capacitor filter in the D/A path (see Functional Block Diagram) to meet
its transfer function specifications, the frequency of its clock input must be 288 kHz. If the clock frequency
is not 288 kHz, the filter transfer function frequencies are frequency-scaled by the ratios of the clock
frequency to 288 kHz:
Normalized Frequency
Internal Timing Configuration (see Figure 2–1)
Absolute Frequency (kHz)
SCF fclock(kHz)
288
For Low-Pass SCF fclock
To obtain the specified filter response, the combination of master clock frequency and the TX(A) counter
and the RX(A) counter values must yield a 288-kHz switched-capacitor clock signal. This 288-kHz clock
signal can then be divided by the TX(B) counter to establish the D/A conversion timing.
The transfer function of the band-pass switched-capacitor filter in the A/D path (see Functional Block
Diagram) is a composite of its high-pass and low-pass transfer functions. When the shift-clock frequency
(SCF) is 288 kHz, the high-frequency roll-off of the low-pass section will meet the band-pass filter transfer
function specification. Otherwise, the high-frequency roll-off is frequency-scaled by the ratio of the
high-pass section SCF clock to 288 kHz (see Figure 5–5). The low-frequency roll-off of the high-pass section
meets the band-pass filter transfer function specification when the A/D conversion rate is 16 kHz. If not, the
low-frequency roll-off of the high-pass section is frequency-scaled by the ratio of the A/D conversion rate
to 16 kHz.
The TX(A) counter and the TX(B) counter are reloaded each D/A conversion period, while the RX(A) counter
and the RX(B) counter are reloaded every A/D conversion period. The TX(B) counter and the RX(B) counter
are loaded with the values in the TB and RB registers, respectively. Via software control, the TX(A) counter
can be loaded with the TA register, the TA register less the TA
register, or the TA register plus the TA
register.
By selecting the TA register less the TA
register option, the upcoming conversion timing occurs earlier by
an amount of time that equals TA
times the signal period of the master clock. If the TA register plus the TA
register
option is executed, the upcoming conversion timing occurs later by an amount of time that equals
TA
times the signal period of the master clock. Thus, the D/A conversion timing can be advanced or
retarded. An identical ability to alter the A/D conversion timing is provided. However, the RX(A) counter can
be programmed via software control with the RA register, the RA register less the RA
register, or the RA
register plus the RA
register.
The ability to advance or retard conversion timing is particularly useful for modem applications. This feature
allows controlled changes in the A/D and D/A conversion timing and can be used to enhance signal-to-noise
performance, to perform frequency-tracking functions, and to generate nonstandard modem frequencies.
If the transmit and receive sections are configured to be synchronous, then the low-pass and band-pass
switched-capacitor filter clocks are derived from the TX(A) counter. Also, both the D/A and A/D conversion
timings are derived from the TX(A) counter and the TX(B) counter. When the transmit and receive sections
are configured to be synchronous, the RX(A) counter, RX(B) counter, RA register, RA
register, and RB
registers are not used.
288 kHz, please call the factory.
(1)
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