Transient response for automatic gain control with multiple intensity thresholds for image-intensified camera
This paper describes the transient response of an automatic gain control (AGC) with multiple thresholds for intensity in an image-intensified camera. Similar examples have flown in intensified-video systems used in satellites. This paper completes the development of a stable AGC with an improved transient response over the system described in a previous work. The improved transient response uses the integrated scene brightness at various intensity thresholds.
Initial results from a photon-counting intensified CCD development
We present a progress report on the development of intensified charge coupled devices (ICCDs) used in both analog mode with CCD integrating the output of an MCP and in photon counting mode where single MCP events are centroided to subpixel accuracy by the CCD and readout electronics. Spatial resolutions of 36 lp/mm have been achieved using a 15 micrometer pitch MCP in the analog mode. In the photon counting mode, individual MCP pores with the same spacing have been easily resolved indicating spatial resolutions of less than 10 micrometer. A discussion of the centroiding algorithms are presented, as well as a description of the electronic designs that will increase the diffuse event rate of the photon counting ICCD to 50,000 events/sec.
Adjustment Speed of Automatic-Volume-Control Systems
The behavior of an a.v.c. amplifier, following a sudden change of input level, is analyzed on the basis of the following assumptions, which are justified in the case of many practical a.v.c. amplifiers: (1) the open-circuit voltage developed by the rectifier is a linear function of the decibel output level of the amplifier; (2) the decibel gain reduction in the controlled stages is a linear function of the gain-control voltage; (3) only one resistance-capacitance filter section is important in delaying delivery of the rectifier output voltage to the gain-control points. It is shown that the last condition is desirable from the standpoint of stability. The analysis shows that, following a sudden change of input level, the fraction (1-1/e) of the decibel gain change required to reach a new equilibrium occurs in (RC)/M seconds. RC is the time constant of the filter section specified in assumption (3), while M, a dimensionless "flatness factor," is defined as the decibel change of input level required to produce a 1-db change of output level, under equilibrium conditions. Further, M = 1 + K1K2, where K1is the rectifier voltage increase per db increase of amplifier output, and K2is the db gain reduction per volt of control. If the change of input level is sufficient in magnitude to cause amplifier overload (or "underload"-stoppage of rectifier action), the control voltage changes with the time constant RC until the overload disappears. Overload may greatly increase the time required for gain readjustment.