dac1205d750 NXP Semiconductors, dac1205d750 Datasheet - Page 27

• Manufacturer Part Number: dac1205d750
• Description: Dac1205d750 Dual 12-bit Dac, Up To 750 Msps; 4? And 8? Interpolating
• Manufacturer: NXP Semiconductors

NXP Semiconductors
DAC1205D750
Product data sheet
10.7.1 NCO in 32-bit
10.7.2 Low-power NCO
10.7.3 Minus_3dB function
10.8 x / (sin x)
When using the NCO, the frequency can be set by the four registers FREQNCO_LSB,
FREQNCO_LISB, FREQNCO_UISB and FREQNCO_MSB over 32 bits.
The frequency for the NCO in 32-bit is calculated as follows:
where M is the decimal representation of FREQ_NCO[31:0].
The phase of the NCO can be set from 0° to 360° by both registers PHINCO_LSB and
PHINCO_MSB over 16 bits.
When using the low-power NCO, the frequency can be set by the 5 MSB of register
FREQNCO_MSB.
The frequency for the low-power NCO is calculated as follows:
where M is the decimal representation of FREQ_NCO[31:27].
The phase of the low-power NCO can be set by the 5 MSB of the register PHINCO_MSB.
During normal use, a full-scale pattern will also be full scale at the output of the DAC.
Nevertheless, when the I and Q data are simultaneously close to full scale, some clipping
can occur and the Minus_3dB function can be used to reduce the gain by 3 dB in the
modulator. This is to keep a full-scale range at the output of the DAC without added
interferers.
Due to the roll-off effect of the DAC, a selectable FIR filter is inserted to compensate for
the x / (sin x) effect. This filter introduces a DC loss of 3.4 dB. The coefficients are
represented in
Table 37.
First interpolation filter
Lower
H(1)
H(2)
H(3)
H(4)
H(5)
f
NCO
f
NCO
=
=
M
--------------
Inversion filter coefficients
M
--------------
2
×
32
2
×
5
f
Table 37 “Inversion filter
All information provided in this document is subject to legal disclaimers.
s
f
s
Rev. 2 — 10 September 2010
Dual 12-bit DAC, up to 750 Msps; 4× and 8× interpolating
Upper
H(9)
H(8)
H(7)
H(6)
-
coefficients”.
DAC1205D750
Value
2
−4
10
−35
401
© NXP B.V. 2010. All rights reserved.
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