AD8319(2005) 데이터 시트보기 (PDF) - Analog Devices

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AD8319
(Rev.:2005)

1 MHz to 10 GHz, 40 dB Log Detector/Controller

Analog Devices 

AD8319

AD8319 VSET PULSE

1

ADL5330 OUTPUT

3

Ch1 2.00V

Ch3 50mVΩ

M10.0μs

A Ch1 2.60V

T 179.800μs

Figure 33. Oscilloscope Screenshot Showing the

Response Time of the AGC Loop

Response time and the amount of signal integration are

controlled by CFLT. This functionality is analogous to the

feedback capacitor around an integrating amplifier. While it is

possible to use large capacitors for CFLT, in most applications

values under 1 nF provide sufficient filtering.

Calibration in controller mode is similar to the method used in

measurement mode. A simple two-point calibration can be

done by applying two known VSET voltages or DAC codes and

measuring the output power from the VGA. Slope and intercept

can then be calculated with the following equations:

Slope = (VSET1 − VSET2)/(POUT1 − POUT2)

(7)

Intercept = POUT1 − VSET1/Slope

(8)

VSETX = Slope × (POUTX − Intercept)

(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

reduced by connecting a ground-referenced capacitor (CFLT) to

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).

ILOG

1.5kΩ

AD8319

+4

3.5pF

VOUT

CLPF

CFLT

Figure 34. Lowering the Postdemodulation Bandwidth

CFLT is selected using the following equation:

CFLT

=

(π

1

× 1.5 kΩ × Video Bandwidth )

−

3.5 pF

(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 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.

2.0

5

1.8

4

1.6

3

1.4

2

1.2

1

1.0

0

0.8

–1

0.6

–2

0.4

–3

0.2

–4

0

–40 –35 –30 –25 –20 –15 –10 –5 0

PIN (dBm)

–5

5

Figure 35. VOUT and Log Conformance vs. Input Amplitude at 10.0 GHz,

Multiple Devices, RTADJ = Open, CLPF = 1000 pF

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.

Rev. 0 | Page 15 of 20

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