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C1 + t1
ǒ
1 *
t2
t3
Ǔ
C2 +
t1 * t2
t3
R1 +
t3
2
t1 (t3 * t2)
t1 +
K
d
K
vco
w
2
d
ǒ
tan f
d
) sec f
d
Ǔ
t2 +
1
w
d
ǒ
tan f
d
) sec f
d
Ǔ
t3 +
tan f
d
) sec f
d
w
d
DAC5687 Passive Interface to Analog Quadrature Modulators
DAC5687
SLWS164E FEBRUARY 2005 REVISED SEPTEMBER 2006
where,
and
charge pump current: iqp = 1 mA
vco gain: K
VCO
= 2 π × G
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 previously with:
Parameter Value Units
G
VCO
1.30E+02 MHz/V
ω d 0.50E+00 MHz
N 4
φ d 80 Degrees
The component values are:
C1 (F) C2 (F) R ( )
3.74E 08 2.88E 10 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.
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 68 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) swing. The voltage at
the TRF3701/2 input pins is centered at 3.7 V and swings 0.76-V
PP
single-ended (1.52-V
PP
differential), or 2.4 dB
of insertion loss.
58 Submit Documentation Feedback Copyright © 2005 2006, Texas Instruments Incorporated
Product Folder Link(s): DAC5687