Starpoint Adaptive Optics

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Hydraplex™ Channel Demultiplexer Unit

Overview

Starpoint's Hydraplex™high channel count deformable mirror drive architecture is intended for large adaptive optics installations. It consists of a standard Channel Demultiplexer Unit that is common to all variants, and a High Voltage Stage that can be designed to provide user-specified drive characteristics.

The HV Stage provides the high voltage power amplifiers needed to drive the deformable mirror. A variety of amplifier types is available, to meet the requirements of a diverse range of deformable mirror characteristics. The Channel Demultiplexer Unit (CDU) provides a Serial FPDP data interface to the control computer, 16-bit DAC outputs to the HV amplifier stage, and read-back of the output from each HV amplifier.

The CDU sits between the control computer and the high voltage stage. It demultiplexes the input digital data stream onto a multi-channel analogue output, which in turn feeds the high voltage amplifiers that drive the deformable mirror. The Channel Demultiplexer Unit features:

A Serial FPDP 246 Mbyte/sec fibre-optic data interface;
A 1664-channel 16-bit DAC output;
A 14-bit ADC read-back of each HV output.

The Hydraplex™ modular rack-based drive architecture separates the data demultiplexer from the high voltage stage. The division of functions between the two sections allows timely design turn-around of custom drive specifications, while providing a standard interface between the control computer and the drive amplifier stage.

The CDU has a 19-inch rack mount form factor. Each 6U unit provides a 1664-channel analogue output and a 1664-channel read-back. Optionally, a 3328-channel output can be configured when read-back isn't required. The Demultiplexer analogue interface is brought out to 68-way 0.8mm pitch VHDCI format connectors. The cables are the popular SCSI-V format widely available from most IT retail outlets.

The Serial FPDP Data Interface

The industry-standard Serial FPDP data interface provides high data bandwidth, low latency, and permits long cable lengths. It has emerged as a preferred interface for large real-time control systems.

The 2.5 Gbaud data link transfers 246 Mbyte/sec each way, giving a 70kHz frame rate for a 1664-channel system. The very simple interface has negligible overhead, allowing these data rates to be attained continuously with very low latency. The drawback is that frame-by-frame data switching is not possible. The interconnect structure remains essentially static after configuration.

A 1.0625 Gbaud interface is also offered as an option, to provide compatibility with earlier Serial FPDP interfaces.

Internal Latency

The Channel Demultiplexer maintains the data bandwidth of the Serial FPDP link through its internal data bus to the DAC outputs. There is no internal buffering of incoming data prior to a DAC write, and each DAC channel is written on the clock cycle on which the data word comes in. The total internal latency budget is shown in the Specification Table.

Output Voltage Monitor

Each HV output is read back to verify its operation. This essential feature enables the Mirror Drive to participate in system-wide self-test in complex systems. Also, the deformable mirror need not endure prolonged exposure to an amplifier fault condition.

Each HV amplifier's output is divided down and fed to a 14-bit A-to-D converter in the Demultiplexer, providing a loop-back test of the amplifier's operation. The Demultiplexer design exploits the high bandwidth and low latency of the serial FPDP data channel to bring the output loop-back data right back to the control computer, allowing full system control from within the user's main Real Time Control architecture.

System Configuration

The Channel Demultiplexer Unit is sized to control about one rack of HV amplifiers. It would typically be configured with its associated high voltage drive in a single 40U × 19" rack, to achieve short and orderly cable routing. It may be located over 100m from its control computer.

The layout on the left illustrates a 1664-channel drive with output voltage read-back. Larger systems are implemented with multiple CDUs, each fed by a separate Serial FPDP link to ensure that data bandwidth scales up with channel count.

Specification


	Digital Input/Output
	Data Interface	Serial FPDP
	Data Symbol Rate	2.5 Gbaud (1.0625 Gbaud option¹)
	Data Physical Connector	Fibre-Optic Duplex LC
	Cable Media	50μm or 62.5μm multi-mode fibre
	Maximum Fibre-Optic Cable Length	300m
	Input Data Rate	120 Msamples/sec. (16-bit samples)
	Output Data Rate	120 Msamples/sec. (16-bit samples)
	Frame Write Rate	70 kHz max. (1664-word frame)
	Control Interface	10/100 Base-T Ethernet, RS232

	Analogue Output
	Output Channels per Unit	1664 (optionally 3328 without read-back)
	Output DAC Resolution	16 bits
	Output DAC Update Rate	120 Msamples/sec.
	Output DAC Frame Rate	70kHz max. (1664-word frame)
	Output Signal Range	± 2.5V
	Output Analogue Signal Connector	68-way 0.8mm pitch VHDCI
	Analogue Signals per Connector	32

	Analogue Input
	Read-back Input Channels per Unit	1664 (optionally 0)
	Input (read-back) ADC Resolution	14 bits
	ADC Conversion Time	10μs (simultaneous sampling, all channels)
	ADC Frame Read Time	110μs (1664-word frame)
	Read-back ADC Frame Rate	8 kHz max. (1664-word frame)
	Input Signal Range	± 5V
	Input Analogue Signal Connector	68-way 0.8mm pitch VHDCI
	Analogue Signals per Connector	32

	Serial FPDP Interoperability
	Link Rates Supported	2.5 Gbaud (1.0625 Gbaud build option¹)
	Serial FPDP Functions Supported	Transmitter and Receiver
	Receiver Flow Control	Always active
	Transmitter Flow Control	Always active (???)
	Receive FIFO size	256k 32-bit words
	CRC Support	Always active
	Transmitter Copy Master Mode	Not supported²
	Receiver Copy Mode	Not supported²
	Receiver Copy/Loop Mode	Not supported²
	Media Supported	Short Wave (850nm) Laser
	Media Connector	Duplex LC
	Fiber Transmit Data Frames Supported	Normal Data Fiber Frames, Sync without Data Fiber Frames
	Transmitter stop in response to NRDY?	Always
	Status updated when no data?	Yes, empty frames transmitted

	Write Latency Budget
	Transmitter to Receiver Latency	<1μs
	Data Receive to DAC Write Latency	<0.1μs
	DAC Settling Time	<15μs

	Physical Characteristics
	Enclosure Dimensions	6U × 19 inch sub-rack
	Power Consumption	50W

¹ The link data rate on an interface is fixed, it is not possible to switch between 2.5 Gbaud and 1.0625 Gbaud rates on a single device. The link rate must be specified as a build option, and cannot be altered in operation.

² The Demultiplexer's Serial FPDP interface is aimed at point-to-point communication for lowest latency. It does not support daisy-chaining, and it does not support non-standard scatter/gather modes. Where elaborate connection topologies are required, a third-party Serial FPDP Switch may be used.

³ All specification data are preliminary and subject to change without notice.