T0370

The application circuit for the T0370 is very simple since most of the critical components are included inside the module. There are several important considerations when using the module in a phone design.

First of all, it is important that the source impedance of the V_CC power supply is very low.This is because the high current demand during the modulation peaks of the CDMA waveform can introduce voltage ripple at the symbol rate that will introduce additional intermodulation distortion or adjacent channel power distortion at the output of the power amplifier. If the power amplifier has a quiescent current of 100 mA and a peak current demand in excess of 1 A, it is possible to see 900 mA change in the current required from V_CC as the modulated signal moves from one extreme to the other. If the power supply source impedance is 1 , the resulting voltage ripple would be 0.9 V which would cause the amplifier to fail in ACP requirements. Generally, the power supply source impedance should be kept as low as possible, preferably below 0.1 ohms total. Most battery technologies used in cellular telephones will support a low source impedance, but it may be necessary to supplement this in some designs with an low ESR capacitor. Ceramic or tantalum capacitors of approximately 10 micro-farads work well for this requirement.

The application circuit includes 100 nF capacitors at each of the PA control lines and V_CC lines to ensure proper RF bypassing. Depending on the phone board layout and circuit bypassing in other areas of the phone, some of these components may not be necessary. There are a number of VCO signals and IF signals used in a given phone design, so it is important to protect the PA module from interfering signals and to limit any interference coming from the PA itself. Care should be taken when removing any of the RF bypassing components.

One final area of concern is with excessive bypassing. If too large a value of bypassing capacitor is used on any of the control lines, it could reduce the frequency response of that control line to the point where a specification failure could occur. Please be sure that the logic lines and regulated supply lines driving the power amplifier control lines are adequate to supply peak current requirements of the bypassing capacitors chosen on the control lines.

The T0370 is a 6 mm × 6 mm 3-V CDMA/AMPS cell-band power-amplifier module designed for use in mobile phones. The module incorporates a SiGe HBT two-stage CDMA / AMPS power-amplifier die. The T0370 is 50-Ohm matched on the input and output allowing the device to be used with minimal external circuitry. Its RF performance meets the requirements for products designed to the IS-95A and B and IS-98 standards.

The T0370 gives excellent RF performance with low current consumption resulting in longer talk times in portable applications. The module features three quiescent current states to minimize current consumption for each output power level. The module has a small 6 mm × 6 mm footprint to allow use in compact phone design.