DAC5687IPZP datasheet(58/79 Pages) TI

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C1 + t1 1 *

C2 +

1 * t2

R1 +

1 (t3 * t2)

t1 +

Kvco

tan f

d )

sec f

t2 +

tan f

d )

sec f

t3 +

tan f

d )

sec f

DAC5687 Passive Interface to Analog Quadrature Modulators

DAC5687

SLWS164E – FEBRUARY 2005 – REVISED SEPTEMBER 2006

where,

and

charge pump current: iqp = 1 mA

vco gain: KVCO = 2π × GVCO rad/V

FVCO/FDATA: N = {2, 4, 8, 16, 32}

phase detector gain: Kd = 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

GVCO

1.30E+02

MHz/V

ωd

0.50E+00

MHz

φd

Degrees

The component values are:

C1 (F)

C2 (F)

R (

Ω)

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-VPP 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-VPP single-ended (2-VPP differential) swing. The voltage at

the TRF3701/2 input pins is centered at 3.7 V and swings 0.76-VPP single-ended (1.52-VPP differential), or 2.4 dB

of insertion loss.

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