ADL5502ACBZ-P2 datasheet(17/28 Pages) AD

17 / 28 page

ADL5502

Rev. A | Page 17 of 28

Multiple RF Inputs

Figure 47 shows a technique for combining multiple RF input

signals to the ADL5502. Some applications can share a single

detector for multiple bands. Three 16.5 Ω resistors in a T-network

combine the three 50 Ω terminations (including the ADL5502

with the shunt 75 Ω matching component). The broadband

resistive combiner ensures each port of the T-network sees a

50 Ω termination. Because there are only 6 dB of isolation from

one port of the combiner to the other ports, only one band

should be active at a time.

ADL5502

RFIN

BAND 1

50Ω

BAND 2

DIRECTIONAL

COUPLER

16.5Ω

50Ω

16.5Ω

DIRECTIONAL

COUPLER

75Ω

Figure 47. Combining Multiple RF Input Signals

LINEARITY

Because the ADL5502 is a linear responding device, plots of

output voltage vs. input voltage result in a straight line (see

Figure 4, Figure 5, and Figure 7) and the dynamic range in

dB is not clearly visible. It is more useful to plot the error on

a logarithmic scale, as shown in Figure 6 and Figure 8. The

deviation of the plot for the ideal straight line characteristic is

caused by input stage clipping at the high end and by signal

offsets at the low end. However, offsets at the low end can be

either positive or negative; therefore, the linearity error vs. input

level plots could also trend upwards at the low end. Figure 10,

Figure 11, Figure 12, Figure 16, Figure 17, and Figure 18 show

error distributions for a large population of devices at specific

frequencies over temperature.

It is also apparent in Figure 6 that the error at the lower portion

of the dynamic range tends to shift up as frequency is increased

This is due to the calibration points chosen, 0 dBm and 9 dBm

(see the Device Calibration and Error Calculation section).

The absolute value cell has an input impedance that varies with

frequency. The result is a decrease in the actual voltage across the

squaring cell as the frequency increases, reducing the conversion

gain. Similarly, conversion gain is less at frequencies near 450 MHz

because of the small on-chip coupling capacitor. The dynamic

range is near constant over frequency, but with a decrease in

conversion gain as frequency is increased.

Output Swing

At 900 MHz, the VRMS output voltage is nominally 1.89 times the

input rms voltage (a conversion gain of 1.89 V/V rms). Similarly,

the PEAK output voltage is nominally 1.27 times the input rms

voltage (a conversion gain of 1.27 V/V rms). The rms output

voltage swings from near ground to 2.4 V on a 3.0 V supply.

Figure 9 shows the output swings of the ADL5502 to a CW input

for various supply voltages. Only at the lowest supply voltage

(2.5 V) is there a reduction in the dynamic range as the input

headroom decreases.

VRMS Output Offset

The ADL5502 has a ±1 dB error detection range of about 30 dB,

as shown in Figure 10 to Figure 12 and Figure 16 to Figure 18. The

error is referred to the best-fit line defined in the linear region of

the output response (see the Device Calibration and Error

Calculation section for more details). Below an input power of

−18 dBm, the response is no longer linear and begins to lose

accuracy. In addition, depending on the supply voltage,

saturation may limit the detection accuracy above 12 dBm.

Calibration points should be chosen in the linear region,

avoiding the nonlinear ranges at the high and low extremes.

100

INPUT (dBm)

–30

–25

–20

–15

–10

–5

Figure 48. VRMS Output vs. Input Level Distribution of 50 Devices,

900 MHz Frequency, Supply 3.0 V

100

INPUT (dBm)

–30

–25

–20

–15

–10

–5

Figure 49. PEAK Output vs. Input Level Distribution of 50 Devices,

900 MHz Frequency, Supply 3.0 V

Figure 48 and Figure 49 show distributions of VRMS and PEAK

output responses vs. the input power for multiple devices. The

ADL5502 loses accuracy at low input powers as the output

response begins to fanout. As the input power is reduced, the

spread of the output response increases along with the error.

ADL5502ACBZ-P2 датащи(PDF) 17 Page - Analog Devices

ADL5502ACBZ-P2 датащи(HTML) 17 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

датащи скачать

ссылки URL