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An array of ring voltage controlled oscillators (RVCO) aiming for photon quantum shot noise limited applications such
as protein crystallography is presented. The pixilated array consists of 24 by 21 RVCO pixels. RVCO pixel converts x-ray
generated input charge into an output oscillating frequency signal. This architecture can be used in both direct and
indirect detection schemes. In this paper the direct detection using a layer of amorphous selenium (a-Se) coupled with
the RVCO array is proposed. Theoretical and Experimental results for an in-house fabricated array of RVCOs in
amorphous silicon (a-Si) technology are presented. All different requirements for protein crystallography application are
listed in this paper and also the way this array addresses each of these requirements is discussed in details in this paper.
The off-panel readout circuitry, designed and implemented in-house, is given in this paper. The off-panel readout circuits
play an important role in the imaging applications using frequency based pixels. They have to be optimized in order to
reduce the fixed pattern noise and fringing effects in an imaging array containing many such RVCO pixels. Since the
frequency of oscillation of each of these pixels is in the range of 100 KHz, there is no antenna effect in the array.
Antenna effect becomes an important issue in other technologies such as poly silicon (poly-Si) and CMOS technologies
due to higher frequency of oscillation ranges (more than 100 MHz). Noise estimations, stability simulations and
measurements for some randomly selected pixels in the array for the fabricated RVCO array are presented. The reported
architecture is particularly promising for large area photon quantum shot noise applications, specifically protein
crystallography. However, this architecture can be used for low dose fluoroscopy, dental computed tomography (CT) and
other large area imaging applications limited by input referred electronic noise due to its very low input referred
electronic noise, high sensitivity and ease of fabrication in low cost a-Si technology.
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