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AD9142A-M5375-EBZ View Datasheet(PDF) - Analog Devices

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AD9142A-M5375-EBZ Datasheet PDF : 72 Pages
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AD9142A
Table 19. Half-Band Filter 2 Coefficient
Lower Coefficient Upper Coefficient
H(1)
H(23)
H(2)
H(22)
H(3)
H(21)
H(4)
H(20)
H(5)
H(19)
H(6)
H(18)
H(7)
H(17)
H(8)
H(16)
H(9)
H(15)
H(10)
H(14)
H(11)
H(13)
H(12)
Integer Value
−2
0
+17
0
−75
0
+238
0
−660
0
+2530
+4096
Table 20. Half-Band Filter 3 Coefficient
Lower Coefficient Upper Coefficient
H(1)
H(11)
H(2)
H(10)
H(3)
H(9)
H(4)
H(8)
H(5)
H(7)
H(6)
Integer Value
+29
0
−214
0
+1209
+2048
DIGITAL MODULATION
The AD9142A provides two modes to modulate the baseband
quadrature signal to the desired DAC output frequency.
Coarse (fS/4) modulation
Fine (NCO) modulation
fS/4 Modulation
The fS/4 modulation is a convenient and low power modulation
mode to translate the input baseband frequency to a fixed fS/4
IF frequency, fS being the DAC sampling rate. When modulation
frequencies other than this frequency are required, the NCO
modulation mode must be used.
NCO Modulation
The NCO modulation mode makes use of a numerically
controlled oscillator (NCO), a phase shifter, and a complex
modulator to provide a means for modulating the signal by a
programmable carrier signal. A block diagram of the digital
modulator is shown in Figure 47. The NCO modulation allows
the DAC output signal to be placed anywhere in the output
spectrum with very fine frequency resolution.
I DATA IN
Data Sheet
I DATA OUT
FTW[31:0]
NCO
PHASE[15:0]
COSINE
~
SINE
Q DATA IN
Q DATA OUT
Figure 47. NCO Modulator Block Diagram
The NCO modulator mixes the carrier signal generated by the
NCO with the I and Q signals. The NCO produces a quadrature
carrier signal to translate the input signal to a new center frequency.
A complex carrier signal is a pair of sinusoidal waveforms of the
same frequency, offset 90° from each other. The frequency of the
complex carrier signal is set via NCO_FTW3 to NCO_FTW0 in
Register 0x31 through Register 0x34.
The NCO operating frequency, fNCO, is always equal to fDAC, the
DACCLK frequency. The frequency of the complex carrier
signal can be set from dc up to ±0.5 × fNCO.
The frequency tuning word (FTW) is in twos complement
format. It can be calculated as
f DAC
2
fCARRIER
f DAC
2
    FTW fCARRIER 232
f DAC
fCARRIER 0
  FTW (1
fCARRIER ) (232 )
f DAC
fCARRIER 0
The generated quadrature carrier signal is mixed with the I and
Q data. The quadrature products are then summed into the I
and Q data paths, as shown in Figure 47.
Updating the Frequency Tuning Word
The frequency tuning word registers are not updated immediately
upon writing, as are other configuration registers. Similar to
FIFO reset, the NCO update can be triggered in two ways.
SPI initiated update
Frame initiated update
Rev. A | Page 34 of 72
 

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