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ML2731CT Arkusz danych(PDF) 10 Page - Micro Linear Corporation |
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ML2731CT Arkusz danych(HTML) 10 Page - Micro Linear Corporation |
10 / 12 page ML2731 10 January, 2000 PRELIMINARY DATASHEET PRELIMINARY VNEG PAEN PDN VBIAS Voltage VPAout current VControl Voltage 0V 3V 0V -3V Current Charge VNEG caps discharge VNEG caps Timeconstant set by external caps on VBIAS >0 µsec >200 µs >0 µsec >0 µsec Timeconstant set by external caps on VPA -7 -6 -5 -4 -3 -2 -1 0 1 10 100 100 Frequency(KHz) 3.3nF 2.2nF 1.5nF 0 20 40 60 80 100 120 140 160 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 5 10 15 20 Time ( µsec) VREF VPA Current RECOMMENDED PA BIAS OPERATION An example of how the PA bias operates is shown in Figure 11. A three-step reference voltage ramp is generated using an external baseband circuit and is applied to the ICON pin via an external resistor. The ML2731 current control loop uses this input as a reference to set the PA current and therefore generates a current ramp output (and hence PA power ramp output.) The rate of change of negative bias and PA current is determined by the capacitance on the VBIAS pin and on the VPA pin. Note sufficient time should be allowed for the negative voltage generator to reach a steady state, prior to enabling the PA. Figure 11: PA Bias Control Loop Operation Figure 12: VPA output vs VREF (TRANSMIT mode, REXT = 12k W, capacitance on VBIAS = 3.3nF) Figure 13: Bandwidth of PA Current control loop for 3.3nF, 2.2nF and 1.5nF VBIAS capacitance FUNCTIONAL DESCRIPTION Where ICON is a fixed value (i.e. the VPA current is not ramped up and down by changing the value of ICON) then the time taken for the VPA current to ramp up following PAEN being enabled is determined by the capacitor values on VBIAS and VPA. The time taken for the current to ramp down following PAEN being disabled is determined by the capacitance value on VPA only. Example timings are: 1 msec ramp-up for 2nF VBIAS capacitance 4 msec ramp-up for 22nF VBIAS capacitance An example of a 3 step current ramp up and ramp down, with 3.3nF capacitance on VBIAS, is shown in Figure 12. |
Podobny numer części - ML2731CT |
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Podobny opis - ML2731CT |
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