Download: Drain-supply-switching of Mobile Phone Power Amps with Pulsed Operation Mode

Drain-supply-switching of Mobile Phone Power Amps with Pulsed Operation Mode

Switching the supply voltage to the drain of a GaAs device is required in many circuits in order to maximise standby times and enable reliable battery charging. Three different concepts for the pulsed switching of the drain supply of a GaAs-device have been evaluated. Each of the three circuits is capable of switching the CGY92 (GSM-power amplifier) to its normal operating point 3V/1.4 Ampères. The pulse operation mode uses a square pulse with a pulse width of 517µs and a pulse ratio of 1:8 (transmit burst of a GSM main stage). For the solution using SIPMOS - transistors another clock with for example 1Vpp f=13MHz is necessarry to generate the appropriate gate voltage. The following overview shows the circuit concepts and an evaluation of the losses in efficiency caused by the voltage drop of the switching element. Overview : Comparison of the different circuits Concept Bipolar PNP-Transistor N-channel SIPMOS P-channel SIPMOS BDP950 BSP319 BSP171 Schematic circuit

PAE

without 40% 40% 40% with switching 38.4% 39% 36.4% difference 1.6% 1% 3.6% Additional 3 Transistors 2 Diodes 2 Diodes component 3 Resistors 2 Transistors 2 Transistorss3Capacitors 2 Resistors 2 Resistors required 4 Capacitors 4 Capacitors 1 Coil/stripline 1 Coil/stripline The overview shows the lowest losses in efficiency for the circuit with SIPMOS BSP319 whereas the circuit with BDP950 needs the smallest number of parts. A detailed description of all three circuits follows. Semiconductor Group 1 Edition A03,

Measured data

Fig. 1 shows a comparison of the three solutions in terms of voltage drop across the switching element. It clearly illustrates that the solutions using N-channel SIPMOS or bipolar transistors have a very low voltage drop thus providing best overall performance of the whole circuit. BDP950 BSP319 BSP171 0,5 0,75 1 1,25 1,5 1,75 I[A] Fig. 1 : Voltage drop of the switching transistor Semiconductor Group 2 Edition A03 U[mV],

Bipolar solution:

Fig.2 : Circuit with bipolar transistor BDP950 T1 BC847PN Dual transistor array T2 BDP950 R Resistor design specific R1 Resistor 470Ohm R2 Resistor 75Ohm R3 Resistor 1kOhm C1 t.b.d. (i.e.10nF) C2 Capacitor 1nF C3 Capacitor 4,7µF RL CGY92-power amp (the load to be switched) Table 2 : Parts list for fig.2 The switching pulse at R1 is amplified by T1 and steers the switching transistor T2. To lower the number of parts and minimise the physical dimensions of the circuit, a doubletransistor BC847PN is used for T1. The capacitor C1 is optional for determining the waveform of the pulse by controlling the switching performance. Semiconductor Group 3 Edition A03,

Circuit with N-channel SIPMOS:

Fig. 3 : Circuit with N-channel SIPMOS BSP319 D1,2 Double Diode BAS70-04 T1 Transistor SMBT3904 T2 SIPMOS BSP319 R1 Resistor 10..30kOhm R2 Resistor 2.2kOhm C1 Capacitor 100pF C2,3 Capacitor 10nF C4 Capacitor 4,7µF L1 t.b.d (4,7µH) RL CGY92-power amp (the load to be switched) Table 3 : Part list for fig.3 The clock signal is amplified by T1 and therefore a superelevated voltage occurs at L1 which is rectified and doubled by D1, D2, C2 and the gate capacitance of T2. The high positive voltage available at the gate of the BSP319 causes the drain-source resistance to become very low in the "on" - status. The "off" - state is caused by switching off T1 by the pulse at R1 and thus also the gate voltage of T2. Semiconductor Group 4 Edition A03,

Circuit with P-channel SIPMOS:

Figure 4 : Circuit with P-channel SIPMOS BSP171 D1,2 Double Diode BAS70-04 T1 Transistor SMBT3904 T2 SIPMOS BSP171 R1 Resistor 10..30kOhm R2 Resistor 2.2kOhm C1 Capacitor 100pF C2,3 Capacitor 10nF C4 Capacitor 4,7µF L1 t.b.d (4,7µH) RL CGY92-power amp (the load to be switched) Table 4 : Parts list for fig. 4 The sinewave from the clock is amplified by T1 and therefore a superelevated voltage occurs at L1 which is rectified and doubled by D1,D2,C2 and the gate conductance of T2. The high negative voltage available at the gate of the BSP171 causes the drain-source resistance to become very low in the "on" - status. The "off" - state is caused by switching off T1 by the pulse at R1 and thus also the gate voltage of T2. Semiconductor Group 5 Edition A03, Published by Siemens AG, Bereich Bauelemente, Terms of delivery and rights to change design reserved. Vertrieb, Produkt-Information, Balanstraße 73, D-81541 München For questions on technology, delivery and prices please contact the Offices of Semiconductor Group in © Siemens AG 1997. All Rights Reserved Germany or the Siemens Companies and Representatives world-wide (see address list). As far as patents or other rights of third parties are concerned, liability is only assumed for components per Due to technical requirements components may se, not for applications, processes and circuits contain dangerous substances. For information on the implemented within components or assemblies. type in question please contact your nearest Siemens Office, Semiconductor Group. The information describes the type of component and shall not be considered as assured characteristics. Siemens AG is an approved CECC manufacturer.

Semiconductor Group 6 Edition A03

]

15