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DAC37J84IAAV Datasheet(数据表) 41 Page - Texas Instruments

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部件型号  DAC37J84IAAV
说明  Digital-to-Analog Converters
下载  122 Pages
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制造商  TI1 [Texas Instruments]
网页  http://www.ti.com
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DAC37J84IAAV Datasheet(HTML) 41 Page - Texas Instruments

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DAC37J84, DAC38J84
www.ti.com
SLASE17B – JANUARY 2014 – REVISED MARCH 2014
With mixer_gain = 0 in config2, the gain through FMIX is sqrt(2)/2 or –3 dB. This loss in signal power is in most
cases undesirable, and it is recommended that the gain function of the QMC block be used to increase the signal
by 3 dB to compensate. With mixer_gain = 1, the gain through FMIX is sqrt(2) or +3 dB, which can cause
clipping of the signal if IIN(t) and QIN(t) are simultaneously near full scale amplitude and should therefore be used
with caution.
7.3.12 Coarse Mixer
In addition to the full complex mixers the DAC37J84/DAC38J84 also has a coarse mixer block capable of shifting
the input signal spectrum by the fixed mixing frequencies ±n × fS/8. Using the coarse mixer instead of the full
mixers will result in lower power consumption.
Treating the two complex channels as complex vectors of the form I(t) + j Q(t), the outputs of the coarse mixer,
IOUT(t) and QOUT(t) are equivalent to:
IOUT(t) = I(t)cos(2πfCMIXt) – Q(t)sin(2πfCMIXt)
QOUT(t) = I(t)sin(2πfCMIXt) + Q(t)cos(2πfCMIXt)
where fCMIX is the fixed mixing frequency selected by cmix=(fs8, fs4, fs2, fsm4). The mixing combinations are
described in Table 15.
Table 15. Coarse Mixer Combinations
Fs/8 MIXER
Fs/4 MIXER
Fs/2 MIXER
-Fs/4 MIXER
cmix(3:0)
MIXING MODE
cmix(3)
cmix(2)
cmix(1)
cmix(0)
0000
Disabled
Disabled
Disabled
Disabled
No mixing
0001
Disabled
Disabled
Disabled
Enabled
–Fs/4
0010
Disabled
Disabled
Enabled
Disabled
Fs/2
0100
Disabled
Enabled
Disabled
Disabled
+Fs/4
1000
Enabled
Disabled
Disabled
Disabled
+Fs/8
1010
Enabled
Disabled
Enabled
Disabled
–3Fs/8
1100
Enabled
Enabled
Disabled
Disabled
+3Fs/8
1110
Enabled
Enabled
Enabled
Disabled
–Fs/8
All others
Not recommended
7.3.13 Dithering
DAC37J84/DAC38J84 supports the addition of a band limited dither to the DAC output after the complex mixer.
This feature is enabled by set dither_ena to “1” and can be useful in reducing the high order harmonics. The
generated dithering sequence can be optionally up-converted to an offset of Fs/2 by setting dither_mixer_ena to
“1”. The added dithering sequence has variable amplitude in 6 dB steps via dither_sra_sel.
7.3.14 Complex Summation
The DAC37J84/DAC38J84 has a complex summation block which is to sum channel A with channel C, channel
B with Channel D, and the resulted complex summation are divided by 2 and sent via channel A and channel B.
This feature is enabled by set output_sum to “1” and can be useful for multi-band application.
7.3.15 Quadrature Modulation Correction (QMC)
7.3.15.1 Gain and Phase Correction
The DAC37J84/DAC38J84 includes a Quadrature Modulator Correction (QMC) block. The QMC blocks provide a
mean for changing the gain and phase of the complex signals to compensate for any I and Q imbalances present
in an analog quadrature modulator. The block diagram for the QMC block is shown in Figure 71. The QMC block
contains 3 programmable parameters.
Registers qmc_gaina/b (10:0) and qmc_gainc/d (10:0) controls the I and Q path gains and is an 11-bit
unsigned value with a range of 0 to 1.9990 and the default gain is 1.0000. The implied decimal point for the
multiplication is between bit 9 and bit 10. The resolution allows suppression to > 65 dBc for a frequency
independent IQ imbalance (the fine delay FIR block also contains gain control through the filter taps or inverse
gain block that allows control with > 20 bits resolution, which can be used to improve the sideband suppression).
Copyright © 2014, Texas Instruments Incorporated
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