A self-compensating built-in self-test solution for RF phased array mismatch

Abstract

An RF Phased array can steer the direction of the beam electronically and it brings about benefits in terms of signal to noise ratio (SNR) and directivity. However, testing the phased array generally requires expensive and high performance RF equipment. This increases production test cost and hampers in-field calibration. We present a low-cost, self-compensating Built-In Self-test (BIST) and calibration solution for RF phased arrays. In our proposed method, we apply a sinusoidal test signal with unknown amplitude to the inputs of two adjacent phased array elements and measure the baseband output signal after down-conversion. Mathematical modeling of the circuit impairments and phased array behavior indicates that by using two distinct input amplitudes, both of which can remain unknown, it is possible to measure the important parameters of the phased array, such as gain and phase mismatch. The BIST circuits are designed and post layout simulations are performed with within-die and die-to-die process variations. Simulations confirm that the BIST circuit provides very accurate results without having to know sinusoidal signal amplitudes or the relation between them. Furthermore, a prototype four-element phased-array PCB was designed and fabricated for verifying our proposed method. With the proposed method, the phase difference between elements can be measured and calibrated with less than 1 error, which would allow for self-monitoring in 6-bit phased array applications.

Process independent gain measurement with low overhead via BIST/DUT co-design

“…However, these technologies are prone to higher process variations and defect rates, which makes RF BIST both more necessary and more challenging. Several techniques in the literature aim to reduce the dependence on external RF instrumentation for low cost testing [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In [2][3][4], simple test signals such as multi-tone sinusoidal signals, are used to generate output data, where the performance of RF transceiver is predicted using the output data as well as machine learning methods.…”

“…In this paper, we propose a BIST solution that is robust with respect to process variations and introduces low performance as well as low area overhead to determine the gain of an RF DUT. Our gain measurement method is similar to the method in [18] with the concept of setting up relative measurements to remove the effect of process variations. Due to the need to use weaker signals, particularly for receivers, we cannot rely on directional couplers, as in [18], that introduce negligible insertion loss and parasitic capacitance.…”

“…Our gain measurement method is similar to the method in [18] with the concept of setting up relative measurements to remove the effect of process variations. Due to the need to use weaker signals, particularly for receivers, we cannot rely on directional couplers, as in [18], that introduce negligible insertion loss and parasitic capacitance. In this work, we use RF switches to direct the signal flow, which inevitably introduce higher parasitics.…”

“…Additionally, the DUT should also operate in the linear region to avoid harmonics. The proposed BIST architecture and circuit implementations in this paper are similar to that of [18]. Major differences are in signal flow components where we use switches to be able to drive/sense a generic DUT with stronger signals and provide better sensitivity.…”

“…We will explain these circuit implementation issues in the next section. The mathematical model for the BIST measurements is identical to [18]. Hence, we skip the model derivation in this paper but summarize the results so as to explain the BIST/DUT co-design methodology better.…”