Modulation transfer function of quadrilinear c.c.d. imager

Herbst, H.; Pfleiderer, H.-J.

doi:10.1049/el:19760518

Cited by 3 publications

(3 citation statements)

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“…Since some charge is lost during each transfer, this step can contribute a blurring of the signal15' 16 …”

Section: (4)mentioning

confidence: 99%

“…In this case the gain is merely given by G=L=i (15) d0 since dt/dq is assumed to be unity. From equations (14) and (15) NEQ = (Jtq MTF ii}2 NEQ(Uq,U,v)= {/lqHd(u,v) H(u,v)Ht(u) Ha(u))2 (16) jç H(u) + Se(u, v) + Sr (u, v)}Ha(u) + Sb (u, v) where the output noise power spectrum is expressed in units of electrons2 area (i.e., variance/spatial frequency2).…”

Section: Noise Equivalent Quantamentioning

confidence: 99%

“…For uniform quantization, from equation (8) is Sb= g = .27 x i0 electrons2 pixel 12 216 The noise power spectrum is the result of the shot, read, and quantization noise components, as in equation (10). The output NEQ can be found from equation (16), and is shown in Fig. 3 plotted versus spatial frequency and mean relative exposure.…”

Section: Computed Examplementioning

confidence: 99%

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<title>Signal-to-noise ratio analysis of charge-coupled device imagers</title>

Burns

1990

Charge-Coupled Devices and Solid State Optical Sensors

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We start with a physical model1 of the detector and associated electronics. Using previously derived expressions for the MTF and noise power spectrum, we extend the use of the model to include a signal-to-noise metric, the noise equivalent quanta (NEQ). This approach is then applied in a design example relevant to film and document scanning. . IntroductionCharge-coupled device (CCD) sensors are now the detector of choice for many electronic imaging applications. For integrated systems, understanding the imaging characteristics of the acquisition step is important since they limit the image information available for processing and display. System design not only involves the integration of various technologies to perform different tasks, but also the comparison of and selection between competing technical options for the same task. A consistent systematic description of signal modulation and noise degradation is valuable when identifying limitations to image quality. In particular, signal-to-noise ratio (SNR) techniques aid in the comparison of competing technologies, and in the evaluation of ultimate performance.The SNR requirements for an image acquisition subsystem are set by the intended application. Determination of these requirements involves consideration of both the input scene information and subsequent image processing and display. For the evaluation of the efficiency with which image information can be acquired the detective quantum efficiency (DQE) is often used.2 The corresponding description of the SNR, for quantum-limited applications, is the noise equivalent quantum (NEQ) exposure.3 Although these metrics were originally applied to photographic film and video cameras, the NEQ has also been used to describe the imaging characteristics of, for example, electrophotographic halftone printing,4'5 laser printers,6'7 astronomical detectors8 and medical diagnostic systems.9'1° The noise equivalent input approach has also been applied to the performance of human 1 The NEQ describes the absolute SNR in terms of an equivalent input quantum exposure. It can, therefore, be used to compare imaging systems and components that use different technologies and physical mechanisms. Here we only address CCD imagers with the goal of expressing the NEQ in terms of the various model design parameters.2 . CCD Imager Model Figure 1 shows a functional block diagram of a CCD sensor in the focal plane of an optical system and its associated electronics. Incident photons are detected in the photosensitive layer simultaneously at each photosite (pixel) location across the detector. The energy released by the absorbed photons generates electron-hole pairs. The electrons then migrate to potential wells in the device so that the collected charge represents the signal integrated over each photosite. This charge, collected during a fixed time interval, is then transferred from the potential wells through a shift register to the readout node. The final step is the readout of the charge packets, analog amplification and quantization of...

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“…Since some charge is lost during each transfer, this step can contribute a blurring of the signal15' 16 …”

Section: (4)mentioning

confidence: 99%

Section: Noise Equivalent Quantamentioning

confidence: 99%

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<title>Signal-to-noise ratio analysis of charge-coupled device imagers</title>

Burns

1990

Charge-Coupled Devices and Solid State Optical Sensors

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Integrierte Detektorschaltungen

Herbst¹

1986

Optoelektronik II

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A 3533 element quadrilinear CCD imager

Sheu

Kadekodi²,

Ngo³

et al. 1983

1983 IEEE International Solid-State Circuits Conference. Digest of Technical Papers

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photosite, 3533-element CCD line imager. The chip was designed in 1.2" long silicon, utilizing two-phase two-level polysilicon gate buried channel technology. Quadrilinear shift registers were implemented to achieve the high resolution, while using moderate design rules for better yield. Complete parallel charge transfer was ensured by employing a structure that eliminated the narrow channel effect. Peripheral and video processing circuits were intergrated on the chip.Conventional CCD line imagers use two readout shift registers. The maximum pixel density of this bilinear design is limited by the minimum poly overlap and spacing design rules in the shift registers. The pixel density can be increased by employing a quadrilinear shift register organization' (Figure 1) to relieve these design rule constraints. However, as the imager resolution and the pixel density increase even further, a new limitation arises due to the narrowing of the CCD parallel transfer channels. This is illustrated in Figure 2, curve A, which shows a conventional quadrilinear cell layout. The charge transfer from the inner shift register to the outer shift register is through the field isolated channel A. The inner shift register has essentially no field confinement in the X direction. For an ultra-high resolution imager, the width of channel A, as confined by the field, is very narrow. This causes a reduction of minimum potential due to the narrow channel effect'. A potential barrier that hinders the charge transfer from the inner shift register to channel A is thus created. The measured minimum potential variation versus the channel width for this conventional design is illustrated in Figure 3, curve A. This curve shows that the minimum potential =tarts t o decrease at l o p channel width. At less than 2 p channel vidth the buried channel changes t o the surface channel.A parallel charge transfer technique was devised to eliminate the charge trapping due to the potential barrier; Figure 2, curve B. The design utilizes the barrier gate in the serial transfer direction t o isolate the charge in the parallel transfer direction also. This poly gate isolation is free from bird's beak and field implant encroachment. Therefore, almost no narrow channel effect occurs. The measured minimum potential versus channel width is illustrated in Figure 3, curve B. This curve shows that the minimum potential is constant down to 4 p channel width.Several peripheral and video processing circuits were integrated on chip to achieve lower overall system cost. These include the clock circuits for the charge detection and the sampling, the Function of Quadrilinear CCD Imager", Electronics Letter, 'Herbst. H. and Pfleiderer, H.J., "Modulation Transfer 2Venkateswaran, V., "Effect of Channel Potential Modulation in Narrow Channel CCD Shift Registers", Proc. IEDM,

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Modulation transfer function of quadrilinear c.c.d. imager

Cited by 3 publications

References 1 publication

<title>Signal-to-noise ratio analysis of charge-coupled device imagers</title>

<title>Signal-to-noise ratio analysis of charge-coupled device imagers</title>

Integrierte Detektorschaltungen

A 3533 element quadrilinear CCD imager

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