AD8317

Rev. 0 | Page 16 of 20

Calibration in controller mode is similar to the method used in

measurement mode. A simple two-point calibration can be

measuring the output power from the VGA. Slope and intercept

can then be calculated with the following equations:

(7)

(8)

(9)

More information on the use of the ADL5330 in AGC

applications 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

the 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

1.5k

Ω

Figure 34. Lowering the Postdemodulation Bandwidth

()

pF

5

.

3

k

5

.

1

1

−

×

Ω

×

=

Bandwidth

Video

C

FLT

π

(10)

The video bandwidth should 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 filtering 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 config-

ured 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 measurement

range.

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

variation, most notably in the intercept, becomes significant.