ADL5902ACPZ-R2 datasheet(22/28 Pages) AD

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ADL5902

Rev. 0 | Page 22 of 28

Table 6. Recommended Minimum CLPF Values for Various Modulation Schemes

Modulation/Standard

Peak-Envelope

Power

Signal

Bandwidth

CLPF (min)

Output Noise

Rise/Fall Time (10% to 90%)

W-CDMA, One-Carrier, TM1-64

10.56 dB

3.84 MHz

10 nF

95 mV p-p

12/330 µs

W-CDMA Four-Carrier, TM1-64, TM1-32,

TM1-16, TM1-8

12.08 dB

18.84 MHz

5.6 nF

164 mV p-p

7/200 µs

LTE, TM1 1CR 20 MHz (2048 Subcarriers,

QPSK Subcarrier Modulation)

11.58 dB

20 MHz

1000 pF

452 mV p-p

1.3/38 µs

OUTPUT VOLTAGE SCALING

The output voltage range of the ADL5902 (nominally 0.3 V to

3.5 V) can be easily increased or decreased. There are a number

of situations where adjustment of the output scaling makes

sense. For example, if the ADL5902 is driving an analog-to-

digital converter (ADC) with a 0 V to 5 V input range, it makes

sense to increase the detector’s nominal maximum output

voltage of 3.5 V so that it is closer to 5 V. This makes better use

of the input range of the ADC and maximizes the resolution of

the system in terms of bits/dB.

If only a part of the ADL5902’s RF input power range is being

used (for example, −10 dBm to −60 dBm), it may make sense to

increase the scaling so that this reduced input range fits into the

ADL5902’s available output swing of 0 V to 4.8 V.

The output swing can also be reduced by simply adding a

voltage divider on the output pin, as shown in Figure 49.

Reducing the output scaling may be used when interfacing the

ADL5902 to an ADC with a 0 V to 2.5 V input range.

The output voltage swing can be increased using a technique

that is analogous to setting the gain of an op amp in non-

inverting mode with the VSET pin being the equivalent of the

inverting input of the op amp.

Connecting VOUT to VSET results in the nominal 0 V to 3.5 V

swing and a slope of approximately 53 mV/dB (this varies

slightly with frequency). Figure 49 and Table 7 show the con-

figurations for increasing the slope, along with recommended

standard resistor values for particular input ranges and output

swings.

VSET

VOUT

VSET

VOUT

Figure 49. Decreasing and Increasing Slope

Table 7. Output Voltage Range Scaling

Desired

Input Range

(dBm)

(Ω)

New

Slope

(mV/dB)

Nominal Output

Voltage Range (V)

0 to −60

665

2000

72.1

0.195 to 4.52

−10 to −50

1180

2000

86.3

1.096 to 4.55

0 to −60

806

2000

38.3

0.103 to 2.49

−10 to −50

324

2000

46.2

0.587 to 2.43

Equation 17 is the general function that governs this.













−

)

(

(17)

where:

VO is the nominal maximum output voltage (see Figure 6

through Figure 18).

V'O is the new maximum output voltage (for example, up

to 4.8 V).

RIN is the VSET input resistance (72 kΩ).

When choosing R1 and R2, attention must be paid to the

current drive capability of the VOUT pin and the input

resistance of the VSET pin. The choice of resistors should not

result in excessive current draw out of VOUT. However, making

R1 and R2 too large is also problematic. If the value of R2 is

compatible with the input resistance of the VSET input (72 kΩ),

this input resistance, which will vary slightly from part to part,

contributes to the resulting slope and output voltage. In general,

the value of R2 should be at least ten times smaller than the

input resistance of VSET. Values for R1 and R2 should, therefore,

be in the 1 kΩ to 5 kΩ range.

It is also important to take into account part-to-part and

frequency variation in output swing along with the ADL5902

output stage’s maximum output voltage of 4.8 V. The VOUT

distribution is well characterized at major frequencies’ bands in

the Typical Performance Characteristics section (see Figure 6

through Figure 8, Figure 12 through Figure 14, Figure 18, and

Figure 19). The resistor values in Table 7, which were calculated

based on 900 MHz performance, are conservatively chosen so

that there is no chance that the output voltages exceed the

ADL5902 output swing or the input range of a 0 V to 2.5 V and

0 V to 5 V ADC. Because the output swing does not vary much

with frequency (it does start to drop off above 3 GHz), these

values work for multiple frequencies.

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