ADL5961ACCZ-R7 datasheet(29/34 Pages) AD

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Data Sheet

ADL5961

APPLICATIONS INFORMATION

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Rev. 0 | 29 of 34

Table 11. IF −3 dB Bandwidth vs. CIF2 with CIF1 = 0 (Continued)

CIF2

f−3dB (MHz)

0.80

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 this 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 bits in Register 0x23, Bits[6:0], and the RGAIN

bits in Register 0x24, Bits[6:0], respectively, in 6 dB steps, as

shown in Table 12. Note that the bit values also must 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 12. 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

24 to 29

30 to 35

36 to 41

42 to 47

48 to 53

…

The adjustable output common-mode level, an up to 8 V p-p out-

put-voltage swing and an up to 200 mA current drive capability, pro-

vides enough flexibility to interface with a broad range of suitable

Σ-Δ, successive approximation register (SAR), or pipeline-based

ADCs with sample rates up to several hundred MHz.

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