DAC1405D650 Datasheet, PDF (26/43 Pages) NXP Semiconductors – Dual 14-bit DAC, up to 650 Msps; 2´ 4´ and 8´ interpolating

NXP Semiconductors
DAC1405D650
Dual 14-bit DAC, up to 650 Msps; 2× 4× and 8× interpolating
10.7 Quadrature modulator and Numerically Controlled Oscillator (NCO)
The quadrature modulator allows the 14-bit I and Q data to be mixed with the carrier
signal generated by the NCO.
The frequency of the NCO is programmed over 32-bit and allows the sign of the sine
component to be inverted in order to operate positive or negative, lower or upper single
sideband up-conversion.
10.7.1 NCO in 32-bit
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:
f _NCO = -^M----₂--^×-₃---₂--^f---^s
(1)
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.
The default setting is f_NCO = 96 MHz when f_s = 640 Msps and the default phase is 0°.
10.7.2 Low-power NCO
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:
f _NCO = -^M-----₂-^×---₅---^f---^s
(2)
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.
10.7.3 Minus 3dB
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.
10.8 x / (sin x)
Due to the roll-off effect of the DAC, a selectable FIR filter is inserted to compensate for
the (sin x) / x effect. This filter introduces a DC loss of 3.4 dB. The coefficients are
represented in Table 34 “Inversion filter coefficients”.
DAC1405D650_1
Product data sheet
Rev. 01 — 4 May 2009
© NXP B.V. 2009. All rights reserved.
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