AD8319

Rev. 0 | Page 15 of 20

A Ch1

2.60V

T

179.800

μs

AD8319 VSET PULSE

ADL5330 OUTPUT

3

1

M10.0

μs

Ch1 2.00V

Ω

T

()

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.

Figure 33. Oscilloscope Screenshot Showing the

Response Time of the AGC Loop

OPERATION BEYOND 8 GHZ

Response time and the amount of signal integration are

feedback capacitor around an integrating amplifier. While it is

values under 1 nF provide sufficient filtering.

The AD8319 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 AD8319

over temperature at 10 GHz when the device is configured as

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

but the AD8319 does provide 30 dB of measurement range within

±3 dB of linearity error.

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)

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

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).

Implementing an impedance match for frequencies beyond 8 GHz

can improve the sensitivity of the AD8319 and measurement

range.

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

most notably in the intercept, becomes significant.

+4

VOUT

CLPF

AD8319

3.5pF

1.5k

Ω

Figure 34. Lowering the Postdemodulation Bandwidth