ADL5960ACCZ-R2 datasheet(26/32 Pages) AD

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Data Sheet

ADL5960

APPLICATIONS INFORMATION

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Rev. A | 26 of 32

by 2 mode can be used standalone or in combination with the offset

frequency interface.

Table 7. Recommended CT2 Band-Pass Filter Settings for LOMODE = 2

CT2

Minimum 2× fLO (GHz)

Maximum 2× fLO (GHz)

Multiply by 4 Mode (LOMODE = 3)

The LO signal is passed first through a frequency doubler, followed

by the band-pass filter tuned through the CT2 bit field, through a

second frequency doubler, and followed by a second band-pass

filter tuned through the CT4 bit field in Register 0x22. Finally, the

signal is passed through the offset mixer to the downconversion

mixers. Table 8 lists the recommended setting for different 4× LO

frequency ranges. The list is not exhaustive. Other valid combina-

tions exist that result in frequency ranges partially or entirely over-

lapping with the recommended settings. This mode can be used

standalone or in combination with the offset frequency interface.

Table 8. Recommended CT2 and CT4 Band-Pass Filter Settings for LOMODE

= 3

CT2

CT4

Minimum 4× fLO (GHz)

Maximum 4× fLO (GHz)

<12

>20

>21

IF SIGNAL PATH CONFIGURATION

The IF signal path following the downconversion mixers can be

configured to optimize the output signal dynamic range and to

achieve optimal interfacing to a wide range of ADCs.

Two cascaded low-pass filters provide programmable IF bandwidth

for suppression of out of band noise and spurious tones. The first

filter provides coarse bandwidth adjustment through the CIF1 bit

field in Register 0x25, as listed in Table 9 and shown in Figure 22.

Table 9. IF −3 dB Bandwidth vs. CIF1 with CIF2 = 0

CIF1

f−3dB (MHz)

CIF1

f−3dB (MHz)

126

13.0

64.0

11.6

41.0

10.5

30.1

9.5

Table 9. IF −3 dB Bandwidth vs. CIF1 with CIF2 = 0 (Continued)

CIF1

f−3dB (MHz)

CIF1

f−3dB (MHz)

24.1

8.8

19.7

8.1

16.7

7.6

14.5

7.0

The second filter provides finely spaced lower bandwidth settings

programmable through the CIF2 bit field in Register 0x25, listed

in Table 10 and shown in Figure 25. Both output channels are

programmed to the same IF bandwidth.

Table 10. IF −3 dB Bandwidth vs. CIF2 with CIF1 = 0

CIF2

f−3dB (MHz)

CIF2

f−3dB (MHz)

126

1.5

11.1

1.3

5.9

1.2

3.8

1.0

3.1

0.99

2.3

0.86

0.80

1.6

0.70

Following the filters are differential output amplifiers with individually

programmable gain. The adjustable gain feature is to accommodate

the actual RF drive level in use, and the feature also enables dy-

namic range optimization of both the forward and reverse channels

over a wide range of port terminations. For example, if the bridge

is terminated with an impedance close to 50 Ω, the bridge output

signal level in the reverse (reflected) channel is much lower than

in the forward (incident) channel. To compensate for this difference,

the reverse channel amplifier can be programmed to a higher gain

setting than the forward channel, so both channels use the full input

dynamic range of the ADC connected to the IF outputs. To achieve

optimal measurement accuracy, a calibration procedure must cover

all used gain setting combinations for the forward and reverse

channels.

The gain for the forward and reverse channel can be programmed

through the FGAIN bit field in Register 0x23 and the RGAIN bit field

in Register 0x24, respectively, in 6 dB steps, as shown in Table 11.

Note that the bit field values also need to be increased in steps

of 6 to select the next gain setting (see Figure 20). Although gain

levels beyond 48 dB are supported, these levels are usually of little

practical significance because amplified noise starts to saturate the

IF channels.

Table 11. IF Amplifier Gain vs. FGAIN and RGAIN Settings

FGAIN, RGAIN

IF Gain (dB)

0 to 5

6 to 11

12 to 17

18 to 23

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