HT8955

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Operating voltage: 5.0VLong delay time

–0.8 seconds (SEL=VSS, 256K DRAM)

–0.2 seconds (SEL=VDD/open, 64K DRAM)25kHz sampling rate

Continuous variable delay time••••••Built-in pre-amplifierLow distortionHigh S/N ratio

Wide frequency response

PCM 10-bit A/D and D/A converters24-pin DIP package

Applications

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Mixers

Karaoke systems••Echo generators

Sound effect generators

General Description

The HT8955A is a CMOS LSI digital audiosignal delay processor. It is designed foraudio system applications including echogenerators, karaoke systems, sound effectgenerators, etc.

The chip consists of a built-in pre-amplifier,on-chip oscillator, DRAM interface, 10-bit A/Dand D/A converters as well as control logic. Itprovides continuously adjustable delay time upto 0.8/0.2 seconds at a sampling rate of 25kHz

when combined with an external DRAM(41256/4164). The HT8955A is superior to aconventional BBD delay unit in its low distor-tion, high S/N ratio and long delay time. Itssophisticated low pass filter will not end in thenormal applications due to the high samplingrate (25~50kHz). Hence, the HT8955A is excel-lent for audio delay system applications. It isoffered in a 24-pin dual-in-line package.

Pin AssignmentBlock Diagram

Pad Coordinates

PadNo.12345678910111213 Chip size: 2170 × 2200 (µm)2

* The IC substrate should be connected to VSS in the PCB layout artwork.

Unit: µm

X–1138.00–1141.00–1136.50–1136.50–1137.00–1149.00–854.50–548.00–198.50111.50461.00773.001122.50Y796.50523.50201.50–163.00–507.00–774.00–853.50–831.50–831.50–831.50–831.50–831.50–831.50PadNo.141516171819202121222325X1141.501141.501141.501141.501141.50896.00645.00435.00335.00150.00–35.00–264.00Y–547.00–197.50111.50461.00770.50811.00810.50794.00794.00779.00779.00806.00Pin Description

Pin No.Pin NameI/O123456789101112BIASINPREOOUTSELOSC1OSC2OSC3OSC4VSSA6A7OIOOIIOIOIOOInternalConnectionOP Non-invertedOP InvertedOP OUTPUT—Pull-High—————CMOS OUTCMOS OUTDescriptionInternal pre-amplifier biasConnects to a decoupling capacitorAudio signal input pin (inverted)Pre-amplifier output pinDelayed audio signal output pinDRAM type selection:VDD or Open: 64KbVSS: 256KbSystem oscillator inputSystem oscillator outputDelay time control oscillator inputDelay time control oscillator outputNegative power supply (GND)Connects to DRAM A6Connects to DRAM A7HT8955AInternalConnectionCMOS OUTCMOS OUTCMOS OUTCMOS OUTCMOS OUTCMOS OUTCMOS OUTCMOS OUTCMOS I/OCMOS I/OCMOS I/O—Pin No.Pin NameI/O131415161718192021222324A5A4A3A2A1A0RASBWRBDATAA8CASBVDDOOOOOOOOI/OOOIDescriptionConnects to DRAM A5Connects to DRAM A4Connects to DRAM A3Connects to DRAM A2Connects to DRAM A1Connects to DRAM A0Connects to DRAM RASBConnects to DRAM WRBData I/O pinConnects to DRAM A8Connects to DRAM CASBPositive power supplyAbsolute Maximum Ratings*

Supply Voltage.................................–0.3V to 6VInput Voltage.................VSS–0.3V to VDD+0.3V

Storage Temperature.................–50°C to 125°COperating Temperature...............–20°C to 70°C

*Note: These are stress ratings only. Stresses exceeding the range specified under “Absolute Maxi-mum Ratings” may cause substantial damage to the device. Functional operation of thisdevice at other conditions beyond those listed in the specification is not implied and prolongedexposure to extreme conditions may affect device reliability.

Electrical Characteristics

SymbolVDDIOPAVAVVIL(Ta=25°C)

ParameterOperating VoltageOperating CurrentPre-amplifier Voltage Gain Comparator Voltage Gain“L” Input VoltageTest ConditionsVDD—5V5V5V—Conditions—No load,fOSC=640kHzRL>100kΩOpen loopRL>100kΩOpen loop—Min.4.5———0Typ.5.02.520002000—Max.5.58——0.3VDDUnitVmAV/VV/VV35th May ’98

HT8955ATest ConditionsVDD—5V5VMaximum Delay TimeTdS/NTHDSignal to Noise RatioTotal Harmonic Distortion5V5V5VSymbolVIHVOMAXTdParameter“H” Input VoltageMaximum Output VoltageConditions—RL>470kΩSEL=open, 25kHzsampling rateSEL=VSS, 25kHzsampling rateVO=1V, 400HzBW=10kHzVO=1V, 400HzBW=7kHzMin.0.7VDD10.150.6——Typ.—1.50.20.8550.5Max.VDD—————UnitVVssdB%Functional Description

The HT8955A is a single chip LSI with an exter-nal DRAM. It is designed for processing audiosignal delay. The chip includes a built-in pre-amplifier, 10-bit A/D and D/A converters. TheA/D and D/A converters ensure low distortion aswell as high S/N ratio of the audio delay system.The chip also provides two sets of oscillationcircuit for system sampling rate and audio echodelay time.

Playing function block diagram

DRAM selection

demands an external resistor between theOSC3 and OSC4 pins. By altering the oscilla-tion resistor, its delay time can be continuouslyadjusted up to 0.8/0.2 seconds at a 25kHz sam-pling rate for DRAM of 256Kb/64Kb.

The HT8955A can interface with a DRAM forstoring delay signals. The type along with themaximum delay time of DRAM is determinedby the status of the SEL pin as shown:System oscillator

SEL ConnectionVDD or OpenVSSDRAMType64Kb256KbDelay Time0.2 seconds0.8 secondsThe HT8955A provides two oscillators, one forthe sampling rate and one for echo delay time.The sampling rate oscillator requires an exter-nal resistor between the OSC1 and OSC2 pins.A higher sampling rate (25~50kHz) can thus bederived by adjusting the oscillation resistorwithout having a sophisticated low pass filter.The delay time oscillator, on the other hand,

4

5th May ’98

Application Circuits

Low cost echo

5HT8955A5th May ’98

Basic KARAOKE system

HT8955ABasic KARAOKE system with pre-emphasis

75th May ’98