A 2x2 array of radial MPD radiators at 120 GHz with integrated self-healing has been designed and is cur- rently being fabricated. A brief summary of the progress on this project is presented below.
A block diagram for this self-healing system is shown in Figure 6.13. Each individual radiator is the same as in the 2x1 radiator described in the previous section. The schematics of the radiator core are also the same, but the sizes of all of the transistors have around doubled to produce higher output power, and the matching networks have been retuned. The phase interpolators and amplitude biasing are controlled locally within the radiator core by on-chip DACs that are controlled by an integrated micro-controller. The sensors employed for this system are DC current sensors to detect the DC power consumption, and mode pickup sensors, that sense the substrate modes and are then mapped to the far field radiation patterns. The updated mode pickup sensors are capable of detecting both phase and amplitude, enabling more accurate mapping of the substrate modes to the radiated field than the amplitude sensors of the first design were able to do.
In terms of radiator performance, the gain of the 2x2 array has a maximum gain of 1.8 dBi which when combined with the output power of the amplifiers of 20 dBm, leads to a simulated effective isotropic radiated power (EIRP) of 21.8 dBm. This version of the chip still has full phase control of the radiator oscillators, so 2Contributions to this project were made by Amirreza Safaripour, Kaushik Dasgupta, Alex Pai, and myself. I was in charge of the antennas and radiation, as well as the locking network distribution. Amirreza programed the digital controller, did the digital routing, the locking oscillator, the circuitry within each radiator, the mode pickup sensors and the healing algorithm. Kaushik designed the digital to analog converters (DACs) and analog to digital converters (ADCs), and Alex designed the DC sensor.
Figure 6.13: Block diagram of the fully integrated self-healing 2x2 MPD radiator array, with substrate mode pickup sensors and DC current sensors, as well as phase actuation for all four radiators and DC operating point bias actuators on the four radiators and the locking network, all controlled by an integrated micro-controller.
Chapter 7
Self-Healing Power Amplifier
7.1
Motivation for Self-Healing
Continual advances in integrated circuit (IC) fabrication have opened up numerous new applications and design possibilities for millimeter-wave (mm-wave) systems that previously were not possible and/or not economically feasible [4, 5, 25, 26]. In addition, improvements in power generation in silicon processes have made silicon power amplifiers (PA’s) viable [27–32, 93]. Making the PA’s in a silicon process allows for greater integration with the rest of the transceiver and reduces the cost. These advances also come with new challenges because with every reduction in minimum feature size, as the industry moves to smaller and smaller process nodes, variation between ICs as well as between transistors within a single IC continues to increase [39–45]. This is compounded by the fact that the digital processing market is the primary driving force behind this scaling, leading to foundries optimizing their device models mainly for digital use. Thus models that are reliable at mm-wave frequencies are often not available early in the node’s development stage. These transistor variations and model inaccuracies, as well as other sources of performance degradation, such as environmental variations, critically impact high power mm-wave designs in nanometer scale CMOS tech- nologies and reduce the yields of such designs. Environmental variations can be caused by many things, but one of the important issues for PA’s is antenna load impedance mismatch [47]. This occurs when the envi- ronment interacts in the near field of the antenna and changes the load impedance looking into the antenna. The ability of PA’s to function properly under load impedance mismatch conditions becomes an especially critical issue when they are being used in a phased array [4, 5, 49–52]. In a phased array, the load impedance that needs to be driven by a PA changes when signal from other nearby elements of the array are coupled back through the antenna. Due to the fact that a mm-wave PA is tuned to provide the optimal impedance to the driving stage, any change in load impedance will be away from that optimal and will degrade the PA’s performance [48]. Other sources of degradation include degradation due to aging [46, 94] and temperature variation.
This chapter will present self-healing as a method to reduce the adverse affects of process and environ- mental variation for mm-wave power amplifier (PA) design. Along the way, the design and measurement of
a proof of concept 28 GHz self-healing power amplifier from [53] will be used as an example to explain the various self-healing concepts1.
Section 7.2 gives an introduction to self-healing and other reconfigurable circuit techniques and presents the design goals and architecture of the example PA, followed by an examination of some of the ways these circuits can be actuated in Section 7.3. A brief overview of the sensors, data converters, and algorithm is then presented in Section 7.4. Finally, a case study of system level measurements of the example PA are then presented in Section 7.5, with concluding remarks in Section 7.6.