Freescale has for several years been working on increasing the frequency range of the 50V technology, and has produced a family of devices for operation at frequencies from UHF through L-band. The first example is the MRF6VP14300H, which delivers 330 W from 1200 to 1400 MHz with a 300 µs pulse width signal and 12% duty cycle at 150 mA quiescent current bias. It was the first reported LDMOS device to deliver this performance at this frequency. Power density is 1.89 W/mm, drain efficiency is more than 59%, and gain is 14 dB in Class C operation. Rise time is less than 60 ns and pulse droop only 0.4 dB. Thermal resistance is 0.13ºC/W and junction temperature remains below 100º C at a flange temperature of 65º C. Power gain and efficiency versus output power at 1.4 GHz is shown in Figure 1.
The device can handle 3-dB input power overdrive and can withstand a 5:1 VSWR mismatch with full phase variation under a 3-dB overdrive condition. With the built-in enhanced ESD protection circuit, the device can operate in Class C with 14 dB of gain. The gate threshold voltage is typically around 1.6 V. Figure 2 shows the test results of Vgs sweep from 1.11 V to 2.23 V, and the operation class shifts from C to B to AB. Input power ranges up to 15 W, which is 3 dB higher than the typical maximum input power of 7.5 W. Power gain in Class C is 3 dB lower than for Class AB although power gain and output power nearly converge when the input power is greater than 12 W.
Figure 3 shows the gain and output power at Vgs of 0.84 V to 1.11 V and 12% duty cycle. Quiescent current is 3 mA. The device is operated in Class C at different Vgs and gain is close at higher input powers. However, the device provides isolation when input power is lower than 500 mW at Vgs of 0.84 V, which is very important for the stability of the host system. The pulse waveform of a pulsed transmitter is its core "ingredient', so slow transistor rise time and power droop within the pulse will produce a commensurate droop at the transmitter output, with a serious negative effect on system performance. This is important as well because many transistors are combined to produce the final output. Rise time of the MRF6VP14300H is less than 60 ns and pulse droop less than 0.4 dB from 1.2 to 1.4 GHz.
1 kW Performance at 450 MHzThe MRF6VP41KH is another example of Freescale's 50-V capabilities, this time at 450 MHz. It can deliver 1 kW peak RF output with a 300-us pulse width (20% duty cycle) input signal. Efficiency is greater than 60% and gain is 17 dB at 450 MHz in Class C operation. It will handle a VSWR of 5:1 with 300 and 500 µs pulses at a 20% duty cycle. In fact, this device can be used in CW applications, where it can deliver 1kW at 352MHz.