AD8330 datasheet(24/28 Pages) AD

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REV. A

–24–

AD8330

INPUT TO AD8330 – dBV

1.0

–50

–40

–20

0.8

0.7

0.6

0.5

–30

0.9

–10

Figure 22. AGC Output vs. Input Amplitude (Simulation)

The upper panel in Figure 23 shows time-domain output for 14

3dB steps in input amplitude from 5.4 mV to 1.7 V. The wave-

forms in Figure 22 show the AGC voltage VDBS.

This simple detector exhibits a temperature variation in the

differential output amplitude of about 4 mV/

°C. It provides a

fast attack time (an increase in the input is quickly leveled to the

nominal output, due to the high peak currents in Q1) and a slow

release time (a decrease in the input is not restored as quickly).

The voltage at the VDBS pin may be used as an RSSI output,

scaled 30 mV/dB. Note that the attack time can be halved by adding

a second transistor as shown in the box (Figure 21). For operation

at lower frequencies, the AGC hold capacitor must be increased.

Wide Range True RMS Voltmeter

The AD8362 is an rms-responding detector providing a dynamic

range of 60 dB from low frequencies to 2.7 GHz. This may be

increased to 110 dB using an AD8330 as a preconditioner, pro-

vided the noise bandwidth is limited by an interstage low-pass or

band-pass filter.

The VGA also provides an input port that is easier to drive

than the 200

Ω input of the AD8362. Figure 24 shows the

general scheme.

Both the AD8330 and AD8362 provide linear-in-decibel control

interfaces. Thus when the output of the latter is used to control

the gain of the former, this functional form is unaffected. The

overall scaling is 33 mV/dB. Figure 25 shows the time domain

response using a loop filter capacitor of 10 nF, for inputs ranging

from 10

µV to 1 V rms, that is, a 100 dB measurement range.

TIME –

–1

–3

100 110 120 130 140 150

–2

–4

0.75

1.25

0.25

1.75

0.50

1.00

1.50

VDBS

OUTPUT

Figure 23. Time Domain Waveforms (Simulation)

(See Text)

OFST

ENBL

CNTR

VPOS

VPS1

VPSO

INHI

OPHI

INLO

OPLO

MODE

CMOP

VMAG

COMM

CMGN

VDBS

AD8330

COMM

CHPF

DECL

INHI

INLO

DECL

PWDN

COMM

ACOM

VREF

VTGT

VPOS

VOUT

VSET

ACOM

CLPF

AD8362

10 F

VOUT

6.04k

4.02k

CFLT

18nF

3.6V

10 F

3.3

0.1 F

INPUT

Figure 24. Wide Range True RMS Voltmeter (Preliminary)

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