a FEATURES Monolithic 10-Bit/75 MSPS Converter ECL Outputs Bipolar (61.75 V) Analog Input 57 dB SNR @ 2.3 MHz Input Low (45 pF) Input Capacitance MIL-STD-883 Compliant Versions Available APPLICATIONS Digital Oscilloscopes Medical Imaging Professional Video Radar Warning/Guidance Systems Infrared Systems 10-Bit 75 MSPS A/D Converter AD9060 FUNCTIONAL BLOCK DIAGRAM MSB LSBS INVERT INVERT 61 59 ANALOG IN 8 9 OVERFLOW +V REF 12 +V SENSE 11 R/2 512 C R O 385 M R/2 3/4 REF 7 P R/2 384 51 OVERFLOW A R GENERAL DESCRIPTION The AD9060 A/D converter is a 10-bit monolithic converter capable of word rates of 75 MSPS and above. Innovative architecture using 512 input comparators instead of the traditional 1024 required by other flash converters reduces input capacitance and improves linearity. Inputs and outputs are ECL-compatible, which makes the AD9060 the recommended choice for systems with conversion rates >30 MSPS to minimize system noise. An overflow bit is provided to indicate analog input signals greater than +VSENSE. R R 257 The AD9060 A/D converter is available in versions compliant with MIL-STD-883. Refer to the Analog Devices Military Products Databook or current AD9060/883B data sheet for detailed specifications. R/2 T R/2 O OVERFLOW 1/2 REF 1 256 R R 49 D8 L OVERFLOW L O G I C 1024 L R 10 47 D6 T 46 D 5 C 23 D4 22 D3 H 21 D2 20 D1 A 19 D0 (LSB) R/2 1/4 REF 63 48 D7 A 129 T R/2 Voltage sense lines are provided to ensure accurate driving of the ± VREF voltages applied to the units. Quarter-point taps on the resistor ladder help optimize the integral linearity of the unit. Either 68-pin ceramic leaded (gull wing) packages or ceramic LCCs are available and specifically designed for low thermal impedances. Two performance grades for temperatures of both 0°C to +70°C and –55°C to +125°C ranges are offered to allow the user to select the linearity best suited for each application. Dynamic performance is fully characterized and production tested at +25°C. MIL-STD-883 units are available. D E C O D E A 50 D9 (MSB) 128 C R H R E 2 S R 1 R/2 –V SENSE 57 –V REF 56 ENCODE 14 ENCODE 13 –VS +V S GROUND REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 © Analog Devices, Inc., 1997 AD9060–SPECIFICATIONS 3/4REF, 1/2REF, 1/4REF Current . . . . . . . . . . . . . . . . . . ± 10 mA Digital Output Current . . . . . . . . . . . . . . . . . . . . . . . . 20 mA Operating Temperature AD9060JE/KE/JZ/KZ . . . . . . . . . . . . . . . . . . 0°C to +70°C Storage Temperature . . . . . . . . . . . . . . . . . . –65°C to +150°C Maximum Junction Temperature2 . . . . . . . . . . . . . . . +175°C Lead Soldering Temp (10 sec) . . . . . . . . . . . . . . . . . . +300°C ABSOLUTE MAXIMUM RATINGS 1 +VS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6 V –VS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –6 V ANALOG IN . . . . . . . . . . . . . . . . . . . . . . . . . . . . –2 V to +2 V +VREF, –VREF, 3/4REF, 1/2REF, 1/4REF . . . . . . . . . –2 V to +2 V +VREF to –VREF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 V ENCODE, ENCODE . . . . . . . . . . . . . . . . . . . . . . . 0 V to –VS (+VS = +5 V; –VS = –5.2 V; 6VSENSE = 61.75 V; ENCODE = 60 MSPS ELECTRICAL CHARACTERISTICS unless otherwise noted) Parameter (Conditions) Temp Test Level RESOLUTION DC ACCURACY3 Differential Nonlinearity Integral Nonlinearity No Missing Codes ANALOG INPUT Input Bias Current4 Input Resistance Input Capacitance4 Analog Bandwidth REFERENCE INPUT Reference Ladder Resistance Ladder Tempco Reference Ladder Offset Top of Ladder Bottom of Ladder Offset Drift Coefficient SWITCHING PERFORMANCE Conversion Rate Aperture Delay (tA) Aperture Uncertainty (Jitter) Output Delay (tOD)5 Output Rise Time Output Fall Time Output Time Slew5 DYNAMIC PERFORMANCE Transient Response Overvoltage Recovery Time Effective Number of Bits (ENOB) fIN = 2.3 MHz fIN = 10.3 MHz fIN = 29.3 MHz Signal-to-Noise Ratio6 fIN = 2.3 MHz fIN = 10.3 MHz fIN = 29.3 MHz Min 3 AD9060JE/JZ Typ Max 10 Min 10 +25°C Full +25°C Full Full I VI I VI VI 1.0 +25°C Full +25°C +25°C +25°C I VI I V V 0.4 +25°C Full Full I VI V +25°C Full +25°C Full Full I VI I VI V +25°C +25°C +25°C +25°C +25°C +25°C +25°C I V V I I I I +25°C +25°C V V +25°C +25°C +25°C I IV IV 8.7 8.0 7.0 9.1 8.6 7.4 +25°C +25°C +25°C I I I 54 51 44 56 54 47 1.25 2.0 7.0 45 175 22 14 37 45 45 1.0 1.25 1.0 1.5 2.0 Guaranteed LSB LSB LSB LSB 1.0 2.0 0.4 1.0 2.0 mA mA kΩ pF MHz 56 66 Ω Ω Ω/°C 90 90 90 90 50 mV mV mV mV µV/°C 1 5 4 1 1 1.5 MSPS ns ps, rms ns ns ns ns 56 66 2.0 7.0 45 175 22 14 37 0.1 90 90 90 90 75 45 45 75 9 3 3 3 2 10 10 –2– Bits 0.75 50 1 5 4 1 1 1.5 Units 1.25 1.5 2.0 2.5 0.1 2 AD9060KE/KZ Typ Max 9 3 3 3 10 10 ns ns 8.7 8.0 7.0 9.1 8.6 7.4 Bits Bits Bits 54 51 44 56 54 47 dB dB dB REV. A AD9060 Temp Test Level Min +25°C +25°C +25°C I I I 54 51 46 56 55 48 54 51 46 58 55 48 dB dB dB +25°C +25°C +25°C I I I 61 55 47 65 58 50 61 55 47 65 58 50 dBc dBc dBc +25°C +25°C +25°C V V V 70 0.5 1 dBc Degree % ENCODE INPUT Logic “1” Voltage Logic “0” Voltage Logic “1” Current Logic “0” Current Input Capacitance Pulse Width (High) Pulse Width (Low) Full Full Full Full +25°C +25°C +25°C VI VI VI VI V I I DIGITAL OUTPUTS Logic “1” Voltage Logic “0” Voltage Full Full VI VI +25°C Full +25°C Full +25°C Full VI VI VI VI VI VI 420 Full VI 6 Parameter (Conditions) DYNAMIC PERFORMANCE (CONTINUED) Signal-to-Noise Ratio6 (Without Harmonics) fIN = 2.3 MHz fIN = 10.3 MHz fIN = 29.3 MHz Harmonic Distortion fIN = 2.3 MHz fIN = 10.3 MHz fIN = 29.3 MHz Two-Tone Intermodulation Distortion Rejection7 Differential Phase Differential Gain POWER SUPPLY +VS Supply Current –VS Supply Current Power Dissipation Power Supply Rejection Ratio (PSRR)8 AD9060JE/JZ Typ Max Min 70 0.5 1 –1.1 AD9060KE/KZ Typ Max –1.1 150 150 5 –1.5 300 300 6 6 150 150 5 –1.5 300 300 6 6 –1.1 –1.1 –1.5 150 2.8 500 500 180 190 3.3 3.5 420 10 6 150 2.8 Units V V µA µA pF ns ns –1.5 V V 500 500 180 190 3.3 3.5 mA mA mA mA W W 10 mV/V NOTES 1 Absolute maximum ratings are limiting values to be applied individually and beyond which the serviceability of the circuit may be impaired. Functional operability is not necessarily implied. Exposure to absolute maximum rating conditions for an extended period of time may affect device reliability. 2 Typical thermal impedances (part soldered onto board): 68-pin leaded ceramic chip carrier: θJC = 1°C/W; θJA = 17°C/W (no air flow); θJA = 15°C/W (air flow = 500 LFM). 68-pin ceramic LCC: θJC = 2.6°C/W; θJA = 15°C/W (no air flow); θJA = 13°C/W (air flow = 500 LFM). 3 3/4REF, 1/2REF and 1/4REF reference ladder taps are driven from dc sources at +0.875 V, 0 V and –0.875 V, respectively. Outputs terminated through 100 Ω to –2.0 V; CL < 4 pF. Accuracy of the overflow comparator is not tested and not included in linearity specifications. 4 Measured with ANALOG IN = +V SENSE 5 Output delay measured as worst-case time from 50% point of the rising edge of ENCODE to 50% point of the slowest rising or falling edge of D 0–D9. Output skew measured as worst-case difference in output delay among D 0–D9. 6 RMS signal to rms noise with analog input signal 1 dB below full scale at specified frequency. 7 Intermodulation measured with analog input frequencies of 2.3 MHz and 3.0 MHz at 7 dB below full scale. 8 Measured as the ratio of the worst-case change in transition voltage of a single comparator for a 5% change m +V S or –VS. Specifications subject to change without notice. REV. A –3– AD9060 EXPLANATION OF TEST LEVELS Test Level I – 100% production tested. II – 100% production tested at +25°C and sample tested at specified temperatures. III – Sample tested only. IV – Parameter is guaranteed by design and characterization testing. V – Parameter is a typical value only. VI – All devices are 100% production tested at +25°C. 100% production tested at temperature extremes for extended temperature devices; sample tested at temperature extremes for commercial/industrial devices. ORDERING GUIDE DIE LAYOUT AND MECHANICAL INFORMATION Device Temperature Range Package Options1 AD9060JZ AD9060JE AD9060KZ AD9060KE AD9060SZ2 AD9060SE2 AD9060TZ2 AD9060TE2 AD9060/PCB 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C –55°C to +125°C –55°C to +125°C –55°C to +125°C –55°C to +125°C 0°C to +70°C Z-68 E-68A Z-68 E-68A Z-68 E-68A Z-68 E-68A Evaluation Board Die Dimensions . . . . . . . . . . . . . . . . 206 × 140 × 15 (± 2) mils Pad Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 × 4 mils Metalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gold Backing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . None Substrate Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –VS Passivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nitride NOTES 1 E = Ceramic Leadless Chip Carrier; Z = Ceramic Leaded Chip Carrier. 2 For specifications, refer to Analog Devices Military Products Databook. CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD9060 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. –4– WARNING! ESD SENSITIVE DEVICE REV. A 1/4 REF NC MSB INVERT GND GND +VS –V S 1/2 REF +VS GND GND +V S –V S ANALOG IN ANALOG IN 3/4REF +VS AD9060 61 60 9 AD9060 TOP VIEW (Not to scale) 26 27 NC LSBs INVERT NC –V SENSE –V REF NC –V S GND GND OVERFLOW D9 (MSB) D8 D7 D6 D5 GND NC GND GND +V S GND GND +VS –V S –V S 44 43 GND –VS –VS +V S ENCODE ENCODE +V S –V S GND GND (LSB) D 0 D1 D2 D3 D4 NC GND NC 10 GND GND +VS +VS –VS NC +VSENSE +VREF AD9060 Pin Designations AD9060 PIN DESCRIPTIONS Pin No. Name Function 1 1/2REF Midpoint of internal reference ladder. 2, 16, 28, 29, 35, 41, 42, 54, 64 –VS Negative supply voltage; nominally –5.2 V ± 5%. 3, 6, 15, 30, 33, 34, 37, 40, 65, 68 +VS Positive supply voltage; nominally +5 V ± 5%. 4, 5, 17, 18, 25, 27, 31, 32, 36, 38, 39, 43, 45, 52, 53, 66, 67 GROUND All ground pins should be connected together and to lowimpedance ground plane. 7 3/4REF Three-quarter point of internal reference ladder. 8, 9 ANALOG IN Analog input; nominally between ± 1.75 V. 11 +VSENSE Voltage sense line to most positive point on internal resistor ladder. Normally +1.75 V. 12 +VREF Voltage force connection for top of internal reference ladder. Normally driven to provide +1.75 V at +VSENSE. 13 ENCODE Differential ECL convert signal that starts digitizing process. 14 ENCODE ECL-compatible convert command used to begin digitizing process. 19–23, 46–50 D0–D9 ECL-compatible digital output data. 51 OVERFLOW ECL-compatible output indicating ANALOG IN > +VSENSE. 56 –VREF Voltage force connection for bottom of internal reference ladder. Normally driven to provide –1.75 V at –VSENSE. 57 –VSENSE Voltage sense line to most negative point on internal resistor ladder. Normally –1.75 V. 59 LSBs INVERT Normally grounded. When connected to +VS, lower order bits (D0–D8) are inverted. Not ECL-compatible. 61 MSB INVERT Normally grounded. When connected to +VS, most significant bit (MSB; D9) is inverted. Not ECL-compatible. 63 1/4REF One-quarter point of internal reference ladder. REV. A –5– AD9060 MIL-STD-883 Compliance Information + 5.0V The AD9060 devices are classified within Microcircuits Group 57, Technology Group D (bipolar A/D converters) and are constructed in accordance with MIL-STD-883. The AD9060 is electrostatic sensitive and falls within electrostatic sensitivity classification Class 1. Percent Defective Allowance (PDA) is computed based on Subgroup 1 of the specified Group A test list. Quality Assurance (QA) screening is in accordance with Alternate Method A of Method 5005. 0.1 µF 3,6,15,30,33,34, 37,40,55,65,68 100 Ω 8 AD1 9 ANALOG IN 510 Ω D0 – D 4 +V S 19 23 510 Ω AD2 14 ENCODE 13 ENCODE 510 Ω AD3 The following apply: Burn-In per 1015; Life Test per 1005; Electrical Testing per 5004. (Note: Group A electrical testing assumes TA = TC = TJ.) MIL-STD-883-compliant devices are marked with “C” to indicate compliance. +2V D5 – D 9 12 56 –2V 510 Ω 46 51 510 Ω AD9060 +V REF –V REF 4,5,17, 18,25,27, 31,32,36, 38,39,43, GROUND LSB INVERT –V S MSB 61 INVERT 2,16,28,29,35, 59 45,52,53,66,67 41,42,54,64 STATIC: AD1 = –2V; AD 2 = ECL HIGH AD3 = ECL LOW DYNAMIC: AD1 = ±2V TRIANGLE WAVE AD2,AD3 = ECL PULSE TRAIN 0.1µF –5.2V AD9060 Burn-ln Connections THEORY OF OPERATION APPLICATIONS Refer to the AD9060 block diagram. As shown, the AD9060 uses a modified “flash,” or parallel, A/D architecture. The analog input range is determined by an external voltage reference (+VREF and –VREF), nominally ± 1.75 V. An internal resistor ladder divides this reference into 512 steps, each representing two quantization levels. Taps along the resistor ladder (1/4REF, 1/2REF and 3/4REF) are provided to optimize linearity. Rated performance is achieved by driving these points at 1/4, 1/2 and 3/4, respectively, of the voltage reference range. Many of the specifications used to describe analog/digital converters have evolved from system performance requirements in these applications. Different systems emphasize particular specifications, depending on how the part is used. The following applications highlight some of the specifications and features that make the AD9060 attractive in these systems. Wideband Receivers Radar and communication receivers (baseband and direct IF digitization), ultrasound medical imaging, signal intelligence and spectral analysis all place stringent ac performance requirements on analog-to-digital converters (ADCs). Frequency domain characterization of the AD9060 provides signal-to-noise ratio (SNR) and harmonic distortion data to simplify selection of the ADC. The A/D conversion for the nine most significant bits (MSBs) is performed by 512 comparators. The value of the least significant bit (LSB) is determined by a unique interpolation scheme between adjacent comparators. The decoding logic processes the comparator outputs and provides a 10-bit code to the output stage of the converter. Receiver sensitivity is limited by the Signal-to-Noise Ratio (SNR) of the system. The SNR for an ADC is measured in the frequency domain and calculated with a Fast Fourier Transform (FFT). The SNR equals the ratio of the fundamental component of the signal (rms amplitude) to the rms value of the “noise.” The noise is the sum of all other spectral components, including harmonic distortion but excluding dc. Flash architecture has an advantage over other A/D architectures because conversion occurs in one step. This means the performance of the converter is limited primarily by the speed and matching of the individual comparators. In the AD9060, an innovative interpolation scheme takes advantage of flash architecture but minimizes the input capacitance, power and device count usually associated with that method of conversion. Good receiver design minimizes the level of spurious signals in the system. Spurious signals developed in the ADC are the result of imperfections in the device transfer function (nonlinearities, delay mismatch, varying input impedance, etc.). In the ADC, these spurious signals appear as Harmonic Distortion. Harmonic Distortion is also measured with an FFT and is specified as the ratio of the fundamental component of the signal (rms amplitude) to the rms value of the worst case harmonic (usually the 2nd or 3rd). These advantages occur because of using only half the normal number of input comparator cells to accomplish the conversion. In addition, a proprietary decoding scheme minimizes error codes. Input control pins allow the user to select from among Binary, Inverted Binary, Twos Complement and Inverted Twos Complement coding (see AD9060 Truth Table). –6– REV. A AD9060 Two-Tone Intermodulation Distortion (IMD) is a frequently cited specification in receiver design. In narrow-band receivers, thirdorder IMD products result in spurious signals in the pass band of the receiver. Like mixers and amplifiers, the ADC is characterized with two, equal amplitude, pure input frequencies. The IMD equals the ratio of the power of either of the two input signals to the power of the strongest third order IMD signal. Unlike mixers and amplifiers, the IMD does not always behave as it does in linear devices (reduced input levels do not result in predictable reductions in IMD). Imaging Visible and infrared imaging systems each require similar characteristics from ADCs. The signal input (from a CCD camera or multiplexer) is a time division multiplexed signal consisting of a series of pulses whose amplitude varies in direct proportion to the intensity of the radiation detected at the sensor. These varying levels are then digitized by applying encode commands at the correct times, as shown below. +FS Performance graphs provide typical harmonic and SNR data for the AD9060 for increasing analog input frequencies. In choosing an A/D converter, always look at the dynamic range for the analog input frequency of interest. The AD9060 specifications provide guaranteed minimum limits at three analog test frequencies. Aperture Delay is the delay between the rising edge of the ENCODE command and the instant at which the analog input is sampled. Many systems require simultaneous sampling of more than one analog input signal with multiple ADCs. In these situations timing is critical, and the absolute value of the aperture delay is not as critical as the matching between devices. Aperture Uncertainty, or jitter, is the sample-to-sample variation in aperture delay. This is especially important when sampling high slew rate signals in wide bandwidth systems. Aperture uncertainty is one of the factors that degrades dynamic performance as the analog input frequency is increased. Digitizing Oscilloscopes Oscilloscopes provide amplitude information about an observed waveform with respect to time. Digitizing oscilloscopes must accurately sample this signal without distorting the information to be displayed. One figure of merit for the ADC in these applications is Effective Number of Bits (ENOBs). ENOB is calculated with a sine wave curve fit and equals: ENOB = N – LOG2 [Error (measured)/Error (ideal)] N is the resolution (number of bits) of the ADC. The measured error is the actual rms error calculated from the converter outputs with a pure sine wave input. The Analog Bandwidth of the converter is the analog input frequency at which the spectral power of the fundamental signal is reduced 3 dB from its low frequency value. The analog bandwidth is a good indicator of a converter’s slewing capabilities. AIN ENCODE Imaging Application Using AD9060 The actual resolution of the converter is limited by the thermal and quantization noise of the ADC. The low frequency test for SNR or ENOB is a good measure of the noise of the AD9060. At this frequency, the static errors in the ADC determine the useful dynamic range of the ADC. Although the signal being sampled does not have a significant slew rate, this does not imply dynamic performance is not important. The Transient Response and Overvoltage Recovery Time specifications ensure that the ADC can track full-scale changes in the analog input sufficiently fast to capture a valid sample. Transient Response is the time required for the AD9060 to achieve full accuracy when a step function is applied. Overvoltage Recovery Time is the time required for the AD9060 to recover to full accuracy after an analog input signal 150% of full scale is reduced to the full-scale range of the converter. Professional Video Digital Signal Processing (DSP) is now common in television production. Modern studios rely on digitized video to create state-of-the-art special effects. Video instrumentation also requires high resolution ADCs for studio quality measurement and frame storage. The AD9060 provides sufficient resolution for these demanding applications. Conversion speed, dynamic performance and analog bandwidth are suitable for digitizing both composite and RGB video sources. The Maximum Conversion Rate is defined as the encode rate at which the SNR for the lowest analog signal test frequency tested drops by no more than 3 dB below the guaranteed limit. REV. A AD9060 –FS –7– AD9060 62 10.0 56 9.0 50 8.0 44 7.0 38 6.0 EFFECTIVE NUMBER OF BITS (ENOB) The AD9060 requires the user to provide two voltage references: +VREF and –VREF. These two voltages are applied across an internal resistor ladder (nominally 37 Ω) and set the analog input voltage range of the converter. The voltage references should be driven from a stable, low impedance source. In addition to these two references, three evenly spaced taps on the resistor ladder (1/4REF, 1/2REF, 3/4REF) are available. Providing a reference to these quarter points on the resistor ladder will improve the integral linearity of the converter and improve ac performance. (AC and dc specifications are tested while driving the quarter points at the indicated levels.) The figure below is not intended to show the transfer characteristic of the ADC but illustrates how the linearity of the device is affected by reference voltages applied to the ladder. The select resistors (RS) shown in the schematic (each pair can be a potentiometer) are chosen to adjust the quarter-point voltage references but are not necessary if R1–R4 match within 0.05%. SIGNAL-TO-NOISE (SNR) – dB USING THE AD9060 Voltage References 1111111111 (NOT TO SCALE) 32 0.4 TAPS DRIVEN 5.0 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 ±VSENSE – Volts OUTPUT CODE 1100000000 AD9060 SNR and ENOB vs. Reference Voltage TAPS FLOATING An alternative approach for defining the quarter-point references of the resistor ladder to evaluate the integral linearity error of an individual device and adjust the voltage at the quarter-points to minimize this error. This may improve the low frequency ac performance of the converter. 1000000000 IDEAL LINEARITY 0100000000 0000000000 –VSENSE 1/4REF 1/2REF VIN 3/4REF +VSENSE Effect of Reference Taps on Linearity Resistance between the reference connections and the taps of the first and last comparators causes offset errors. These errors, called “top and bottom of the ladder offsets,” can be nulled by using the voltage sense lines, +VSENSE and –VSENSE, to adjust the reference voltages. Current through the sense lines should be limited to less than 100 µA. Excessive current drawn through the voltage sense lines will affect the accuracy of the sense line voltage. The next page shows a reference circuit that nulls out the offset errors using two op amps, and provides appropriate voltage references to the quarter-point taps. Feedback from the sense lines causes the op amps to compensate for the offset errors. The two transistors limit the amount of current drawn directly from the op amps; resistors at the base connections stabilize their operation. The 10 kΩ resistors (R1–R4) between the voltage sense lines form an external resistor ladder; the quarter point voltages are taken off this external ladder and buffered by an op amp. The actual values of resistors R1–R4 are not critical, but they should match well and be large enough (≥10 kΩ) to limit the amount of current drawn from the voltage sense lines. –8– Performance of the AD9060 has been optimized with an analog input voltage of ± 1.75 V (as measured at ± VSENSE). If the analog input range is reduced below these values, relatively larger differential nonlinearity errors may result because of comparator mismatches. As shown in the figure below, performance of the converter is a function of ± VSENSE. Applying a voltage greater than 4 V across the internal resistor ladder will cause current densities to exceed rated values and may cause permanent damage to the AD9060. The design of the reference circuit should limit the voltage available to the references. Analog Input Signal The signal applied to ANALOG IN drives the inputs of 512 parallel comparator cells (see Equivalent Analog Input figure). This connection has a typical input resistance of 7 kΩ and input capacitance of 45 pF. The input capacitance is nearly constant over the analog input voltage range as shown in the graph, which illustrates that characteristic. The analog input signal should be driven from a low distortion, low noise amplifier. A good choice is the AD9617, a wide bandwidth, monolithic operational amplifier with excellent ac and dc performance. The input capacitance should be isolated by a small series resistor (24 Ω for the AD9617) to improve the ac performance of the amplifier (see AD9060/PCB Evaluation Board Block Diagram). REV. A AD9060 +5V +VSENSE ANALOG INPUT 150Ω 1/2 AD708 0.1µF +VREF 12 +VSENSE 11 * +1.75V R/2 R1 10kΩ RS +0.875V 1/2 AD708 3/4 REF R/2 7 R/2 0.1µF R2 10kΩ 1/2 REF TO COMPARATORS R R +2.5V +1.75V AD580 356Ω 3/4REF R RS 150Ω RS RS 0V R/2 1/2 AD708 1/2 REF 1 R/2 0.1µF R R3 10kΩ 1/4REF R –0.875V R/2 1/2 AD708 1/4 REF 63 R/2 0.1µF R4 10kΩ –V SENSE R AD9060 Equivalent Analog Input R R 20kΩ R/2 20kΩ –VSENSE 57 –V REF 56 –1.75V 1/2 AD708 150Ω 0.1µF GROUND * * = WIRING RESISTANCE = < 5Ω DIGITAL BITS AND OVERFLOW AD9060 –5V AD9060 Equivalent Digital Outputs AD9060 Reference Circuit GROUND ENCODE 14 13 ENCODE –VS –VS AD9060 Encode and Encode Equivalent Circuits REV. A –9– AD9060 ANALOG INPUT N N+1 ta ENCODE N N+1 ENCODE tOD DATA OUTPUT DATA FOR N + 1 DATA FOR N ta – Aperture Delay tOD – Output Delay AD9060 Timing Diagram Timing In the AD9060, the rising edge of the ENCODE signal triggers the A/D conversion by latching the comparators. (See the AD9060 Timing Diagram.) These ENCODE and ENCODE signals are ECL compatible and should be driven differentially. Jitter on the ENCODE signal will raise the noise floor of the converter. Differential signals, with fast clean edges, will reduce the jitter in the signal and allow optimum ac performance. In applications with a fixed, high frequency encode rate, converter performance is also improved (jitter reduced) by using a crystal oscillator as the system clock. The AD9060 units are designed to operate with a 50% duty cycle encode signal; adjustment of the duty cycle may improve the dynamic performance of individual devices. Since the ENCODE and ENCODE signals are differential, the logic levels are not critical. Users should remember, however, that reduced logic levels will reduce the slew rate of the edges and effectively increase the jitter of the signal. ECL terminations for the ENCODE and ENCODE signals should be as close as possible to the AD9060 package to avoid reflections. In systems where only single-ended signals are available, the use of a high speed comparator (such as the AD96685) is recommended to convert to differential signals. An alternative is to connect +1.3 V (ECL midpoint) to ENCODE and drive the ENCODE connection single ended. In such applications, clean, fast edges are necessary to minimize jitter in the signal. Output data of the AD9060, D0–D9 and OVERFLOW are also ECL compatible and should be terminated through 100 Ω to –2 V (or an equivalent load). cluded in the data sheet limits. Performance of the overflow indicator is dependent on circuit layout and slew rate of the encode signal. The operation of this function does not affect the other data bits (D0–D9). It is not recommended for applications requiring a critical measure of analog input voltage. Layout and Power Supplies Proper layout of high speed circuits is always critical but is particularly important when both analog and digital signals are involved. Analog signal paths should be kept as short as possible and be properly terminated to avoid reflections. The analog input voltage and the voltage references should be kept away from digital signal paths; this reduces the amount of digital switching noise that is capacitively coupled into the analog section of the circuit. Digital signal paths should also be kept short, and run lengths should be matched to avoid propagation delay mismatch. Terminations for ECL signals should be as close as possible to the receiving gate. In high speed circuits, layout of the ground circuit is a critical factor. A single, low impedance ground plane on the component side of the board will reduce noise on the circuit ground. Power supplies should be capacitively coupled to the ground plane to reduce noise in the circuit. Multilayer boards allow designers to lay out signal traces, without interrupting the ground plane, and provide low impedance power planes. Data Format It is especially important to maintain the continuity of the ground plane under and around the AD9060. In systems with dedicated digital and analog grounds, all grounds of the AD9060 should be connected to the analog ground plane. The format of the output data (D0–D9) is controlled by the MSB INVERT and LSBs INVERT pins. These inputs are dc control inputs and should be connected to GROUND or +VS. The AD9060 Truth Table gives information to choose from among Binary, Inverted Binary, Twos Complement and Inverted Twos Complement coding. The power supplies (+VS and –VS) of the AD9060 should be isolated from the supplies used for external devices; this further reduces the amount of noise coupled into the A/D converter. Sockets limit the dynamic performance and should be used only for prototypes or evaluation—PCK Elastomerics Part No. CCS6855 is recommended for the LCC package. (Tel. 215-672-0787) The OVERFLOW output is an indication that the analog input signal has exceeded the voltage at +VSENSE. The accuracy of the overflow transition voltage and output delay are not tested or in- An evaluation board is available to aid designers and provide a suggested layout. –10– REV. A AD9060 30 10.0 50 8.0 +25°C 7.0 44 –55°C & +125°C 6.0 38 32 5.0 26 4.0 20 1 2 4 6 8 10 20 40 60 100 35 40 HARMONICS – dBc 9.0 EFFECTIVE NUMBER OF BITS (ENOB) SIGNAL-TO-NOISE (SNR) – dB ENCODE RATE = 60MSPS 56 +125°C 45 –55°C 50 55 60 +25°C 65 70 200 1 2 INPUT FREQUENCY – MHz 50 8.0 44 7.0 38 6.0 32 5.0 26 4.0 20 40 60 CONVERSION RATE – MSPS 80 48 100 > + 1.7500 + 1.7466 + 1.7432 . . . +0.0034 0.000 –0.0034 . . . – 1.7432 – 1.7466 < – 1.7466 40 CAPACITANCE 46 30 45 20 44 10 –1.2 –0.6 0 +0.6 ANALOG INPUT (A IN ) – Volts +1.8 Twos Complement True MSB INV = “0” LSBs INV = “0” Inverted MSB INV = “1” LSBs INV = “1” True MSB INV = “1” LSBs INV = “0” Inverted MSB INV = “0” LSBs INV = “1” (1)1111111111 1111111111 1111111110 . . . 1000000000 0111111111 0111111110 . . . 0000000010 0000000001 0000000000 (l)0000000000 0000000000 0000000001 . . . 0111111111 1000000000 1000000001 . . . 1111111101 1111111110 1111111111 (1)0111111111 0111111111 0111111110 . . . 0000000000 1111111111 1111111110 . . . 1000000010 1000000001 1000000000 (1)1000000000 1000000000 1000000001 . . . 1111111111 0000000000 0000000001 . . . 0111111101 0111111110 0111111111 The overflow bit is always 0 except where noted in parentheses ( ). MSB INVERT and LSBs INVERT are considered dc controls. AD9060 Truth Table REV. A +1.2 Input Capacitance/Resistance vs. Input Voltage Offset Binary 1024 1023 1022 . . . 512 511 510 . . . 02 01 00 50 RESISTANCE 47 –1.8 AD9060 SNR and ENOB vs. Conversion Rate Range 0 = –1.75 V FS = +1.75 V 100 60 INPUT CAPACITANCE – pF ANALOG INPUT = 2.3MHz EFFECTIVE NUMBER OF BITS (ENOB) SIGNAL-TO-NOISE (SNR) – dB 9.0 56 60 70 10.0 62 Step 40 AD9060 Harmonics vs. Input Frequency AD9060 SNR and ENOB vs. Input Frequency 20 10 4 6 8 10 20 INPUT FREQUENCY – MHz INPUT RESISTANCE – kΩ 62 –11– AD9060 DAC OUT +5V AD9712 DAC IOUT 50Ω D BUFFERED ANALOG INPUT DUT ANALOG INPUT 400Ω +5V +VS GND MSB INVERT LSBs INVERT J2 200Ω 50Ω –VS TO ERROR WAVEFORM CIRCUIT C1349b–1–5/97 –5V U5 AD9617 24Ω ANALOG INPUT TO ERROR WAVEFORM CIRCUIT +VREF AD9060 DUT D D D2 D3 D4 D5 D D D6 D D D D D7 D8 +VSENSE REFERENCE CIRCUIT (LSB) D0 D1 3/4REF (MSB) D9 D D 1/2REF OVERFLOW D OUTPUT DATA CONNECTOR Q ECL LATCHES DATA READY CLK 1/4REF –VSENSE ENCODE –VREF DIFFERENTIAL ECL CLOCK TIMING CIRCUIT ENCODE AD9060/PCB Evaluation Board Block Diagram AD9060/PCB EVALUATION BOARD The AD9060/PCB Evaluation Board is available from the factory and is shown here in block diagram form. The board includes a reference circuit that allows the user to adjust both references and the quarter-point voltages. The AD9617 is included as the drive amplifier, and the user can configure the gain from –1 to –15. Onboard reconstruction of the digital data is provided through the AD9712, a 12-bit monolithic DAC. The analog and reconstructed waveforms can be summed on the board to allow the user to observe the linearity of the AD9060 and the effects of the quarter-point voltages. The digital data and an adjustable Data Ready signal are available via a 37-pin edge connector. OUTLINE DIMENSIONS Dimensions shown in inches and (mm). Leaded Ceramic Chip Carrier Suffix Z PRINTED IN U.S.A. Leadless Chip Carrier (LCC) Suffix E –12– REV. A