DAC5687 Datasheet, PDF (56/72 Pages) Texas Instruments – 16-BIT, 500 MSPS 2x-8x INTERPOLATING DUAL-CHANNEL DIGITAL-TO-ANALOG CONVERTER (DAC)

DAC5687
SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
www.ti.com
ǒ Ǔ C1 +
t1
1
*
t2
t3
C2
+
t1
*
t3
t2
R1
+
t1
t3²
(t3 *
t2)
(1)
where,
ǒ Ǔ t1
+
KdKvco
w
2
d
tan f_d ) sec f_d
ǒ Ǔ ^{t2 +}
1
w_d tan f_d ) sec f_d
t3
+
tan
f_d
) sec
w_d
f_d
(2)
and
charge pump current: iqp = 1 mA
vco gain: K_VCO = 2πxG_VCO rad/V
FVCO/FDATA: N = {2, 4, 8, 16, 32}
phase detector gain: K_d = iqp × (2 × N) – 1 A/rad
An Excel spreadsheet is provided by Texas Instruments for automatically calculating the values for C1, C2, and
R.
Completing the example given above with:
Parameter
G_VCO
ωd
N
φd
Value
1.30E+02
0.50E+00
4
80
Units
MHz/V
MHz
Degrees
The component values are:
C1 (F)
3.74E-08
C2 (F)
2.88E-10
R (Ω)
9.74E+01
As the PLL characteristics are not sensitive to these components, the closest 20% tolerance capacitor and 1%
tolerance resistor values can be used. If the calculation results in a negative value for C2 or an unrealistically
large value for C1, then the phase margin may need to be reduced slightly.
DAC5687 Passive Interface-to-Analog Quadrature Modulators
The DAC5687 has a maximum 20-mA full-scale output and a compliance range of AVDD ±0.5 V. The TRF3701
or TRF3702 analog quadrature modulators (AQM) require a common-mode of approximately 3.7 V and 1.5 V to
2-V_PP differential swing. A resistive network as shown in Figure 65 can be used to translate the common mode
voltage between the DAC5687 and TRF3701 or TRF3702. The voltage at the DAC output pins for a full-scale
sine wave is centered at approximately AVDD with a 1-V_PP single ended (2-V_PP differential). The voltage at the
TRF3701/2 input pins is centered at 3.7 V and swings 0.76-V_PP single ended (1.56-V_PP differential), or 2.4 dB of
insertion loss.
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