LTC5599 datasheet(20/42 Pages) LINER

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LTC5599

5599f

For more information www.linear.com/LTC5599

applicaTions inForMaTion

able 2. Differential Baseband (BB) Input Impedance vs

Frequency for EN = High and VCMBB = 1.4V

FREQUENCY

(MHz)

INPUT IMPEDANCE (

REFL

COEFFICIENT

REAL*

IMAG* (CAP)

MAG

ANGLE

LO FREQUENCY = 92MHz (REGISTER 0x00 = 0x79), DIGITAL GAIN = –4dB

1.90k

–7.17k (22.2pF)

0.900

–1.6

1.76k

–1.82k (21.9pF)

0.893

–6.3

1.25k

–751 (21.2pF)

0.854

–15

678

–429 (18.6pF)

0.755

–27

342

–308 (12.9pF)

0.585

–39

LO FREQUENCY = 150MHz (REGISTER 0x00 = 0x62), DIGITAL GAIN = –4dB

1.90k

–9.11k (17.5pF)

0.900

–1.3

1.82k

–2.30k (17.3pF)

0.896

–5.0

1.45k

–935 (17.0pF)

0.872

–12

887

–507 (15.7pF)

0.804

–23

441

–325 (12.2pF)

0.658

–36

100

226

–252 (6.3pF)

0.457

–51

LO FREQUENCY = 500MHz (REGISTER 0x00 = 0x2D), DIGITAL GAIN = –4dB

1.91k

–14.7k (10.6pF)

0.900

–0.8

1.89k

–3.74k (10.7pF)

0.899

–3.0

1.72k

–1.50k (10.7pF)

0.891

–7.7

1.35k

–769 (10.4pF)

0.864

–15

786

–426 (9.4pF)

0.785

–27

100

323

–251 (6.4pF)

0.583

–47

200

212

–190 (4.2pF)

0.478

–65

LO FREQUENCY = 500MHz (REGISTER 0x00 = 0x2D), DIGITAL GAIN = 0dB

1.56k

–15.0k (10.6pF)

0.879

–0.8

1.56k

–3.84k (10.4pF)

0.880

–3.0

1.48k

–1.52k (10.4pF)

0.874

–7.5

1.21k

–784 (10.2pF)

0.849

–15

753

–432 (9.2pF)

0.776

–27

100

323

–251 (6.3pF)

0.582

–47

200

213

–190 (4.2pF)

0.478

–65

LO FREQUENCY = 900MHz (REGISTER 0x00 = 0x12), DIGITAL GAIN = –4dB

1.91k

–17.0k (9.4pF)

0.901

–0.7

1.90k

–4.3k (9.3pF)

0.900

–2.7

1.77k

–1.72k (9.3pF)

0.893

–6.7

1.46k

–878 (9.1pF)

0.873

–13

915

–475 (8.4pF)

0.811

–24

100

371

–261 (6.1pF)

0.622

–45

200

233

–193 (4.1pF)

0.506

–62

able 2. Differential Baseband (BB) Input Impedance vs

Frequency for EN = High and VCMBB = 1.4V

FREQUENCY

(MHz)

INPUT IMPEDANCE (

REFL

COEFFICIENT

REAL*

IMAG* (CAP)

MAG

ANGLE

EN = Low (Chip Disabled, REGISTER 0X00 = 0x2E)

2.04k

–18.2k (8.8pF)

0.906

–0.6

2.02k

–4.59k (8.7pF)

0.906

–2.5

1.91k

–1.84k (8.7pF)

0.901

–6.3

1.59k

–935 (8.5pF)

0.893

–12

1.01k

–502 (7.9pF)

0.826

–23

100

402

–269 (5.9pF)

0.644

–43

200

246

–197 (4.0pF)

0.522

–60

*Parallel Equivalent

Thecircuitisoptimizedforacommonmodevoltageof1.4V

which can be internally or externally applied. In case of AC-

coupling to the baseband pins (1.4V internally generated

bias) make sure that the high pass filter corner is not

affecting the low frequency components of the baseband

signal. Even a small error for low baseband frequencies

can result in degraded EVM.

The baseband input offset voltage depends on the source

resistance. In case of AC-coupling the 1 sigma offset is

about 1.1mV, resulting in about –46.6dBm LO leakage.

For shorted baseband pins (0Ω source resistance), the

LO leakage improves to about –50.1dBm. In case of AC-

coupling the LO leakage can be reduced by connecting a

resistor in parallel with the baseband inputs, thus lower-

ing baseband input impedance and offset. Further, the

low combined baseband input leakage current of 1.3nA

in shutdown mode retains the voltage over the coupling

capacitors, which helps to settle faster when the part is

enabled again. It is recommended to drive the baseband

inputsdifferentiallytoimprovethelinearity.WhenaDACis

used as the signal source, a reconstruction filter should be

placedbetweentheDACoutputandtheLTC5599baseband

inputs to avoid aliasing.

Internal Gain Trim DACs

Four internal gain trim DACs (one for each baseband pin)

are configured as 11-bit each. The usable DAC input value

range is integer continuous from 64 to 2047 and 0 for

shutdown. The DACs are not intended for baseband signal

(continued)

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