DAC5687MPZPEP datasheet(57/75 Pages) TI1

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C1 + t1 1 *

C2 +

1 * t2

R1 +

1 (t3 * t2)

(1)

t1 +

Kvco

tan f

d )

sec f

t2 +

tan f

d )

sec f

t3 +

tan f

d )

sec f

(2)

DAC5687 Passive Interface-to-Analog Quadrature Modulators

DAC5687-EP

SGLS333 – JUNE 2006

where,

and

charge pump current: iqp = 1 mA

vco gain: K

VCO = 2πxGVCO 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

Completing the example given above 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 66 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). The voltage at the

TRF3701/2 input pins is centered at 3.7 V and swings 0.76-VPP single ended (1.56-VPP differential), or 2.4 dB of

insertion loss.

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