The Current Mode Class D Amplifier for Microwave Frequencies

1
The Current Mode Class D Amplifier for Microwave
Frequencies
H. Kobayashi, J. Hinrichs, L. Larson and P.
Asbeck UCSD Fuji Electric Co., Ltd.
2
Voltage Mode (Switching) Class-D
3
Output Capacitance Loss
VDD
VDD
Ron
Cout

• Energy is lost at each voltage
  change

• Loss doesnt depend on Ron

4
The Basic CircuitCurrent Mode Class-D
5
Other Advantages

• If both devices are on at same timeVoltage Mode
  Class-D efficiency decreasesCurrent Mode Class-D
  efficiency is unchanged
• If both devices are off at same time, CMCD
  efficiency decreasesVMCD efficiency is unchanged

6
Spice Simulations of CMCD
Pout 272mW Drain Efficiency 79.2
V
Output Voltage
V
Out(-), Out()
A
M1, M2 0.5um nMOS (from MOSIS) width 5mm Cdb
8pF Frequency 1GHz Rload 50 ohm In(),
In(-) 2Vp-p, Gate Bias 1v Filter Q 5
Time ns
Id1
Ids1(exclude Cout Current)
7
Practical Demonstration using GaAs FET
Device Infineon CLY5 Balun 50ohm coaxial cable
balun Rload 50ohm L filter 34n H C filter
2p F C out 8 pF
External Caps. (8pF/each)
8
Experimental Results
Pout
VDD 2.5V Power Input 50mW DC Power
367mW Power Output 282mW Drain Efficiency
76.9 PAE 66.1 (include Balun Loss) (Gate Bias
-1.4v)
D. Eff.
Output power mW
Efficiency
PAE
Input Power dBm
9
Conclusion

• Current-Mode Class-D for RF applications have
  been demonstrated.
• CMCD is potentially superior to normal Voltage
  Mode Class-D (due to ZVS)
• More detailed Analysis and Power Gain Improvement
  are our future work.