Data Sheet

AD8317

Rev. C | Page 15 of 19

Figure 33 shows the response of the AGC RF output to a pulse

responds with an RF burst. In this configuration, the input

signal to the ADL5330 is a 1 GHz sine wave at a power level

of −15 dBm.

A CH1

2.48V

T

699.800µs

AD8317 VSET PULSE

ADL5330 OUTPUT

2

1

T

M10.0µs

CH1 2.00V

Figure 33. Oscilloscope Screenshot Showing

the Response Time of the AGC Loop

Response time and the amount of signal integration are con-

capacitor around an integrating amplifier. Although it is

values under 1 nF provide sufficient filtering.

Calibration in controller mode is similar to the method used

in measurement mode. A simple 2-point calibration can be

measuring the output power from the VGA. Slope and intercept

can then be calculated by:

(9)

(10)

(11)

More information on the use of the ADL5330 in AGC applica-

tions can be found in the ADL5330 data sheet.

OUTPUT FILTERING

For applications in which maximum video bandwidth and,

consequently, fast rise time are desired, it is essential that the

CLPF pin be left unconnected and free of any stray capacitance.

The nominal output video bandwidth of 50 MHz can be reduced

CLPF pin, as shown in Figure 34. This is generally done to

reduce output ripple (at twice the input frequency for a

symmetric input waveform such as sinusoidal signals).

+4

VOUT

CLPF

AD8317

3.5pF

1.5kΩ

Figure 34. Lowering the Postdemodulation Bandwidth

pF

5

.

3

)

kΩ

5

.

1

2

(

1









Bandwidth

Video

C

FLT



(12)

The video bandwidth must typically be set to a frequency equal

to about one-tenth the minimum input frequency. This ensures

that the output ripple of the demodulated log output, which is at

twice the input frequency, is well filtered.

In many log amp applications, it may be necessary to lower

the corner frequency of the postdemodulation filter to achieve

low output ripple while maintaining a rapid response time to

changes in signal level. An example of a 4-pole active filter is

shown in the AD8307 data sheet.

OPERATION BEYOND 8 GHz

The AD8317 is specified for operation up to 8 GHz, but it provides

useful measurement accuracy over a reduced dynamic range of

up to 10 GHz. Figure 35 shows the performance of the AD8317

over temperature at 10 GHz when the device is configured as

shown in Figure 22. Dynamic range is reduced at this frequency,

but the AD8317 does provide 30 dB of measurement range

within ±3 dB of linearity error.

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

–40

–35

–30

–25

–20

–15

–10

–5

0

5

–5

–4

–3

–2

–1

0

1

2

3

4

5

Implementing an impedance match for frequencies beyond

8 GHz can improve the sensitivity of the AD8317 and measure-

ment range.

Operation beyond 10 GHz is possible, but part-to-part

variation, most notably in the intercept, becomes significant.