When a DC-DC converter is in proximity to the Power Amplifier (PA) in an RF transmitter, regardless of whether or not it's positioned on the high or on the base of the antenna tower, the switching action of the converter is a possible source of RF interference. Many features of TDK-Lambda’s PAH450S sequence of power modules present safeguards in opposition to this. For instance, the sealed casting of this module successfully acts as a containment protect for radiated EMI generated by the converter that could possibly be sensed and amplified by the RF PA. Performed EMI can also be a priority, with the chief sources being carried out EMI from the converter enter again onto the availability bus, and voltage ripple on the converter’s output being coupled into the PA.
To suppress carried out EMI, RF Power Amplifier clients typically design their very own enter filters. Pointers for carried out emissions requirements typically cease at 30 MHz, whereas the everyday frequency vary for the PAs is between 800 MHz to 2 GHz. Due to this fact, these requirements are primarily directed at guarding in opposition to potential interference with different RF tools sharing the PA’s power bus. This precaution might be in comparison with warning pacemaker sufferers about staying away from microwave ovens; the danger could also be slight, however the penalties might be drastic.
The compact dimension (half brick) of TDK-Lambda’s PAH450S dc-dc converter offers a high power density appropriate for driving analog PAs in built-in modules for base-station functions.
Relating to external interference, in addition to the potential interference from the converter’s output voltage ripple, whereas normal tips are utilized to stop RF interference, this danger can also be minimized by the truth that the RF and power converter frequency domains are considerably totally different. Due to this fact, with cautious design practices, RF interference from the converter shouldn't be a serious concern, although as converter’s switching frequencies enhance it might turn into a major design subject.
As well as, thermal points signify a major problem within the design of transmitters, particularly in a mixed PA/converter module. In configurations the place the converter and the RF PA are co-packaged as a single module and put in on the high of the tower (different configurations hold the whole RF transmit stage on the base of the tower), even modest positive aspects in effectivity can have large efficiency benefits.
For instance, an enchancment in converter effectivity from 90% to 92% can result in complete warmth reductions of as much as 20% within the mixed module. The much less warmth produced by the converter, the extra RF output power that may be generated by Power Amplifier, which is normally the driving parameter for the transmit path.
Packaged in a regular half-brick case, these DC-DC converters can be found with 28V or 48V outputs, and attain efficiencies as much as 92%. Digital power management may appear to carry the potential to introduce additional single-digit percentages in gained effectivity. Nonetheless, our buyer’s inform us, to emulate the equal operation of an analog management loop working at 1MHz (for instance), the clocking frequency of a digital controller must be considerably increased, which may then hasten the arrival of increased RF interferences with the RF PA in future techniques.
Different advances, primarily in RF power device applied sciences similar to SiC and GaN semiconductors, can have a larger impression on the general effectivity of transmitters than digital power management. For now, converters with analog management such because the PAH450S sequence signify a strong option for powering analog PAs.
Power provides wanted for the PAs of next-generation base station functions are additionally confronted with a number of different necessities. These embody the power to resist excessive ambient temperature swings, compact dimension, and a large output adjustment vary to permit the consumer to optimize the amplifier’s efficiency. TDK-Lambda’s PAH450S sequence of 450 W dc-dc converter modules are designed to satisfy these calls for. For instance, many cell repeaters are configured as three separate single-pole antennas, every 2 ft to 3 ft tall, mounted in a triangular configuration on a 200 ft to 300 ft tower. Every pole sometimes has a separate RF PA and dc-dc converter. A power bus is routed up the tower, and the large enter vary spanned by the 48V version of the converter (36V to 76Vdc) is very tolerant of the voltage drop that may happen alongside the size of the power bus, which may vary from 6V to 7Vdc.