KMB-001LEVALZ datasheet(17/33 Pages) RENESAS

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ISLA224P12

FN7983 Rev.4.01

Page 17 of 32

Apr 8, 2024

Analog Input

A single fully differential input (VINP/VINN) connects to the

sample and hold amplifier (SHA) of each unit A/D. The ideal

full-scale input voltage is 2.0V, centered at the VCM voltage of

0.94V, as shown in Figure 29.

Best performance is obtained when the analog inputs are driven

differentially. The common-mode output voltage, VCM, should be

used to properly bias the inputs, as shown in Figures 30 through

32. An RF transformer will give the best noise and distortion

performance for wideband and/or high intermediate frequency

(IF) inputs. Two different transformer input schemes are shown in

Figures 30 and 31.

This dual transformer scheme is used to improve common-mode

rejection, which keeps the common-mode level of the input

matched to VCM. The value of the shunt resistor should be

determined based on the desired load impedance. The

differential input resistance of the ISLA224P12 is 600Ω.

The SHA design uses a switched capacitor input stage (see

Figure 45), which creates current spikes when the sampling

capacitance is reconnected to the input voltage. This causes a

disturbance at the input, which must settle before the next

sampling point. Lower source impedance will result in faster

settling and improved performance. Therefore a 2:1 or 1:1

transformer and low shunt resistance are recommended for

optimal performance.

A differential amplifier, as shown in the simplified block diagram

in Figure 32, can be used in applications that require

DC-coupling. In this configuration, the amplifier will typically

dominate the achievable SNR and distortion performance. The

ISL552xx differential amplifier family can also be used in certain

AC applications with minimal performance degradation.

FIGURE 27. TYPICAL SNR PERFORMANCE vs TEMPERATURE,

DEVICE CALIBRATED AT +85°C, fIN = 105MHz

FIGURE 28. TYPICAL SFDR PERFORMANCE vs TEMPERATURE,

DEVICE CALIBRATED AT +85°C, fIN = 105MHz

Temperature Calibration (Continued)

73.50

73.75

74.00

74.25

74.50

74.75

75.00

TEMPERATURE (°C)

-2dBFS ANALOG INPUT

-1dBFS ANALOG INPUT

-2dBFS ANALOG INPUT

-1dBFS ANALOG INPUT

TEMPERATURE (°C)

FIGURE 29. ANALOG INPUT RANGE

1.0

1.8

0.6

0.2

1.4

VINP

VINN

VCM

0.94V

1.0V

FIGURE 30. TRANSFORMER INPUT FOR GENERAL PURPOSE

APPLICATIONS

ADT1-1WT

0.1µF

A/D

VCM

ADT1-1WT

1000pF

FIGURE 31. TRANSMISSION-LINE TRANSFORMER INPUT FOR

HIGH IF APPLICATIONS

A/D

VCM

1000pF

TX-2-5-1

ADTL1-12

FIGURE 32. DIFFERENTIAL AMPLIFIER INPUT

A/D

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