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ADL5331 Datenblatt(PDF) 10 Page - Analog Devices |
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ADL5331 Datenblatt(HTML) 10 Page - Analog Devices |
10 / 15 page ADL5331 Data Sheet Rev. A | Page 10 of 15 10nF 10nF INHI INLO RFOUT RFIN 10nF 10nF OPHI OPLO ADL5331 RF VGA 120nH 120nH 5V ETC1-1-13 Figure 17. Single-Ended Drive with Balanced Output The device can be driven single-ended with similar perfor- mance, as shown in Figure 17. The single-ended input interface can be implemented by driving one of the input terminals and terminating the unused input to ground. To achieve the optimal performance, the output must remain balanced. In the case of Figure 17, a transformer balun is used at the output. GAIN CONTROL INPUT When the VGA is enabled, the voltage applied to the GAIN pin sets the gain. The input impedance of the GAIN pin is 1 MΩ. The gain control voltage range is between 0.1 V and 1.4 V, which corresponds to a typical gain range between −15 dB and +15 dB. The 1 dB input compression point remains constant at 3 dBm through the majority of the gain control range, as shown in Figure 7 through Figure 9. The output compression point increases decibel for decibel with increasing gain setting. The noise floor is constant up to VGAIN = 1 V where it begins to rise. The bandwidth on the gain control pin is approximately 3 MHz. Figure 10 shows the response time of a pulse on the VGAIN pin. Although the ADL5331 provides accurate gain control, precise regulation of output power can be achieved with an automatic gain control (AGC) loop. Figure 18 shows the ADL5331 in an AGC loop. The addition of a log amp or a TruPwr™ detector (such as the AD8362) allows the AGC to have improved temperature stability over a wide output power control range. Note that the ADL5331, because of its positive gain slope, in an AGC application requires a detector with a negative VOUT/ RFIN slope. As an example, the AD8319 in the example in Figure 19 has a negative slope. The AD8362 rms detector, however, has a positive slope. Extra circuitry is necessary to compensate for this. To operate the ADL5331 in an AGC loop, a sample of the output RF must be fed back to the detector (typically using a directional coupler and additional attenuation). A setpoint voltage is applied to the VSET input of the detector while VOUT is connected to the GAIN pin of the ADL5331. Based on the detector’s defined linear-in-dB relationship between VOUT and the RFIN signal, the detector adjusts the voltage on the GAIN pin (the detector’s VOUT pin is an error amplifier output) until the level at the RF input corresponds to the applied setpoint voltage. The VGAIN setting settles to a value that results in the correct balance between the input signal level at the detector and the setpoint voltage. The detector’s error amplifier uses CLPF, a ground-referenced capacitor pin, to integrate the error signal (in the form of a current). A capacitor must be connected to CLPF to set the loop bandwidth and to ensure loop stability. INLO INHI GAIN OPLO OPHI DIRECTIONAL COUPLER ATTENUATOR VPOS COMM ADL5331 5V 5V CLPF VOUT VSET RFIN LOG AMP OR TruPwr DETECTOR DAC RFIN Figure 18. ADL5331 in AGC Loop |
Ähnliche Teilenummer - ADL5331_17 |
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Ähnliche Beschreibung - ADL5331_17 |
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