|Description||1 MHz to 10 GHz, 45 dB Log Detector/Controller|
|AD8319ACPZ-R7 Datasheet PDF : 20 Pages |
The basic connections for operating the AD8319 in an automatic
gain control (AGC) loop with the ADL5330 are shown in
Figure 30. The ADL5330 is a 10 MHz to 3 GHz variable gain
amplifier. It offers a large gain control range of 60 dB with
±0.5 dB gain stability. This configuration is similar to Figure 29.
The gain of the ADL5330 is controlled by the output pin of the
AD8319. This voltage, VOUT, has a range of 0 V to near VPOS.
To avoid overdrive recovery issues, the AD8319 output voltage
can be scaled down using a resistive divider to interface with the
0 V to 1.4 V gain control range of the ADL5330.
A coupler/attenuation of 21 dB is used to match the desired
maximum output power from the VGA to the top end of the
linear operating range of the AD8319 (approximately −5 dBm
at 900 MHz).
Figure 30. AD8319 Operating in Controller Mode to Provide Automatic Gain
Control Functionality in Combination with the ADL5330
Figure 31 shows the transfer function of the output power vs.
the VSET voltage over temperature for a 900 MHz sine wave with
an input power of −1.5 dBm. Note that the power control of the
AD8319 has a negative sense. Decreasing VSET, which corresponds
to demanding a higher signal from the ADL5330, increases gain.
The AGC loop is capable of controlling signals of ~40 dB. This
range limitation is due to the dynamic range of the AD8319.
Using a wider dynamic range detector such as the AD8317,
AD8318, or AD8362 will allow for the full 60dB range of the
ADL5330 to be utilized. The performance over temperature is
most accurate over the highest power range, where it is gener-
ally most critical. Across the top 40 dB range of output power,
the linear conformance error is well within ±0.5 dB over
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6
SETPOINT VOLTAGE (V)
Figure 31. ADL5330 Output Power vs. AD8319 Setpoint Voltage,
PIN = −1.5 dBm
For the AGC loop to remain in equilibrium, the AD8319 must
track the envelope of the ADL5330’s output signal and provide
the necessary voltage levels to the ADL5330’s gain control input.
Figure 32 shows an oscilloscope screenshot of the AGC loop
depicted in Figure 30. A 100 MHz sine wave with 50% AM
modulation is applied to the ADL5330. The output signal from
the VGA is a constant envelope sine wave with amplitude
corresponding to a setpoint voltage at the AD8319 of 1.3 V.
Also shown is the gain control response of the AD8319 to the
changing input envelope.
AM MODULATED INPUT
2 ADL5330 OUTPUT
CH1 200mV Ch2 200mV
A Ch2 1.03V
T 0.00000 s
Figure 32. Oscilloscope Screenshot Showing an AM Modulated Input Signal
and the Response from the AD8319
Figure 33 shows the response of the AGC RF output to a pulse
on VSET. As VSET decreases from 1.5 V to 0.4 V, the AGC loop
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.
Rev. 0 | Page 14 of 20
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