Colinear 20-Bit Monolithic Audio DIGITAL-TO-ANALOG CONVERTER

Transcription

1 Colinear 0-Bit Monolithic Audio DIGITAL-TO-ANALOG CONVERTER FEATURES COLINEAR 0-BIT AUDIO DAC NEAR-IDEAL LOW LEVEL OPERATION GLITCH-FREE OUTPUT ULTRA LOW 9dB max THDN (Without External Adjustment) db SNR min (A-Weight Method) INDUSTRY STD SERIAL INPUT FORMAT FAST (00ns) CURRENT OUTPUT (±ma; ±% max) CAPABLE OF x OVERSAMPLING COMPLETE WITH REFEREE DESCRIPTION The is a precision 0-bit digital-to-analog converter with ultra-low distortion ( 9dB max with a full scale output; -K). Incorporated into the is a unique Colinear dual-dac per channel architecture that eliminates unwanted glitches and other nonlinearities around bipolar zero. The also features a very low noise (db max SNR; A-weighted method) and fast settling current output (00ns typ, ma step) which is capable of -times oversampling rates. Applications include very low distortion frequency synthesis and high-end consumer and professional digital audio applications. V Analog V Digital V Analog V Digital Upper B Adj Lower B Adj Clock Latch Enable Data 0 Input Shift Register and Control Logic Upper DAC Positive Data Latches Lower DAC Negative Data Latches 9-Bit Upper DAC 9-Bit Lower DAC Colinear 0-Bit DAC 9 0 RFEEDBACK RFEEDBACK IOUT Buried Zener Reference Servo Amp Ref Amp Bipolar Offset Current Offset Decouple Reference Decouple Servo Decouple Potentiometer Voltage Analog Common Digital Common Colinear, Burr-Brown Corp. International Airport Industrial Park Mailing Address: PO Box 00 Tucson, AZ Street Address: 0 S. Tucson Blvd. Tucson, AZ 0 Tel: (0) - Twx: Cable: BBRCORP Telex: 0-9 FAX: (0) 9-0 Immediate Product Info: (00) Burr-Brown Corporation PDS-0E Printed in U.S.A. October, 99

2 SPECIFICATIONS ELECTRICAL All specifications at C and ±V A and ±V D = ±V, unless otherwise noted., -J, -K PARAMETER CONDITIONS MIN TYP MAX UNITS RESOLUTION 0 Bits DYNAMIC RANGE, ΤΗDΝ at 0dB Referred to Full Scale 9 00 db -J 00 0 db -K 0 0 db DIGITAL INPUT Logic Family TTL/CMOS Compatible Logic Level: V IH. V D V V IL 0 0. V I IH V IH =.V µa I IL V IL = 0.V 0 µa Data Format Serial, MSB First, BTC () Input Clock Frequency. MHz TOTAL HARMONIC DISTORTION N (), Without Adjustments f = 99Hz (0dB) () f S =.khz () 9 db f = 99Hz ( 0dB) f S =.khz 0 db f = 99Hz ( 0dB) f S =.khz 0 db -J f = 99Hz (0dB) f S =.khz 9 9 db f = 99Hz ( 0dB) f S =.khz db f = 99Hz ( 0dB) f S =.khz 0 db -K f = 99Hz (0dB) f S =.khz 00 9 db f = 99Hz ( 0dB) f S =.khz db f = 99Hz ( 0dB) f S =.khz db ACCURACY Level Linearity at 90dB Signal Level ±0. ± db Gain Error ± ± % Bipolar Zero Error () ±0 mv Gain Drift 0 C to 0 C ppm/ C Bipolar Zero Drift 0 C to 0 C ppm of FSR/ C Warm-up Time Minute IDLE CHANNEL SNR () 0Hz to 0kHz at BPZ () 0 db POWER SUPPLY REJECTION db ANALOG OUTPUT Output Range ±.00 ma Output Impedance 0 Ω Internal R FEEDBACK. kω Settling Time ma Step 00 ns Glitch Energy No Glitch Around Zero POWER SUPPLY REQUIREMENTS ±V A, ±V D Supply Voltage Range ±.0 ± ±.0 V I A, I D Combined Supply Current V A, V D = V 0 ma I A, I D Combined Supply Current V A, V D = V ma Power Dissipation ±V A, ±V D = ±V 00 mw TEMPERATURE RANGE Specification 0 0 C Operating 0 C Storage 0 00 C NOTES: () Binary Two s Complement coding. () Ratio of (Distortion RMS Noise RMS ) / Signal RMS. () D/A converter output frequency (signal level). () D/A converter sample frequency ( x.khz; x oversampling). () Offset error at bipolar zero. () Measured using an OPA and.kω feedback and an A-weighted filter. () Bipolar Zero. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems.

3 PIN ASSIGNMENTS PIN DESCRIPTION MNEMONIC P Servo Amp Decoupling Capacitor CAP P V Analog Supply Voltage V A P Reference Decoupling Capacitor CAP P Offset Decoupling Capacitor CAP P Bipolar Offset Current Output (ma) BPO P DAC Current Output (0 to ma) I OUT P Analog Common Connection ACOM P No Connection P9 Feedback Resistor Connection (.kω) RF P0 Feedback Resistor Connection (.kω) RF P V Digital Supply Voltage V D P Digital Common Connection DCOM P V Digital Voltage Supply V D P No Connection P No Connection P No Connection P No Connection P DAC Data Clock Input CLK P9 No Connection P0 DAC Data Latch Enable LE P DAC Data Input DATA P No Connection P Optional Upper DAC Bit- Adjust (.9V)* UB Adj P Optional Lower DAC Bit- Adjust (.9V)* LB Adj P Bit Adjust Reference Voltage Tap (.V)* V POT P No Connection P No Connection P V Analog Supply Voltage V A *Nominal voltages at these nodes assuming ±V A ; ±V D = ±V. ABSOLUTE MAXIMUM RATINGS V A, V D to ACOM/DCOM... 0V to V V A, V D to ACOM/DCOM... 0V to V V A, V D to V A, V D... 0V to V ACOM to DCOM... ±0.V Digital Inputs (pins, 0, ) to DCOM... V to V D Power Dissipation... 00mW Lead Temperature, (soldering, 0s) C Max Junction Temperature... C Thermal Resistance, θ JA... 0 C/W NOTE: Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to absolute maximum conditions for extended periods may affect device reliability. PACKAGE INFORMATION PACKAGE DRAWING MODEL PACKAGE NUMBER () -Pin Plastic DIP -J -Pin Plastic DIP -K -Pin Plastic DIP NOTE: () For detailed drawing and dimension table, please see end of data sheet, or Appendix D of Burr-Brown IC Data Book. ORDERING INFORMATION TEMPERATURE MAX THDN, USA OEM PRICES MODEL PACKAGE RANGE AT 0dB Pin Plastic DIP 0 C to 0 C db $.0 $9.0 $. -J -Pin Plastic DIP 0 C to 0 C 9dB K -Pin Plastic DIP 0 C to 0 C 9dB

4 TYPICAL PERFORMAE CURVES All specifications at C and ±V A and ±V D = ±.0V, unless otherwise noted. THDN (db) THDN vs FREQUEY 0 0dB 0 0dB 0 0dB 00 0dB k 0k Output Frequency (Hz) Deviation from Ideal Level (db) 0 0 -BIT LEVEL LINEARITY (Dithered Fade to Noise) Output Signal Level (db). -BIT MONOTONICITY 0 90dB SIGNAL SPECTRUM (00Hz Bandwidth) Output Voltage (mv) Power Spectrum (db) ms/div 0 0 k k k k 0k Frequency (Hz) 00 90dB SIGNAL (0Hz to 0kHz Bandwidth) 0 0dB SIGNAL (0Hz to 0kHz Bandwidth) Output Level (µv) Output Level (µv) Time (µs) Time (µs)

5 THEORY OF OPERATION DUAL-DAC COLINEAR ARCHITECTURE Digital audio systems have traditionally used laser-trimmed, current-source DACs in order to achieve sufficient accuracy. However even the best of these suffer from potential lowlevel nonlinearity due to errors at the major carry bipolar zero transition. More recently, DACs employing a different architecture which utilizes noise shaping techniques and very high oversampling frequencies, have been introduced ( Bitstream, MASH, or -bit DACs). These DACs overcome the low level linearity problem, but only at the expense of signal-to-noise performance, and often to the detriment of channel separation and intermodulation distortion if the succeeding circuitry is not carefully designed. The PCM is a new solution to the problem. It combines all the advantages of a conventional DAC (excellent full scale performance, high signal-to-noise ratio and ease of use) with superior low-level performance. Two DACs are combined in a complementary arrangement to produce an extremely linear output. The two DACs share a common reference and a common R-R ladder to ensure perfect tracking under all conditions. By interleaving the individual bits of each DAC and employing precise laser trimming of resistors, the highly accurate match required between DACs is achieved. This new, complementary linear or dual-dac Colinear approach, which steps away from zero with small steps in both directions, avoids any glitching or large linearity errors and provides an absolute current output. The low level performance of the is such that real 0-bit resolution can be realized, especially around the critical bipolar zero point. Table I shows the conversion made by the internal logic of the from binary two s complement (BTC). Also, the resulting internal codes to the upper and lower DACs (see front page block diagram) are listed. Notice that only the LSB portions of either internal DAC are changing around bipolar zero. This accounts for the superlative performance of the in this area of operation. DISCUSSION OF SPECIFICATIONS DYNAMIC SPECIFICATIONS Total Harmonic Distortion Noise The key specification for the is total harmonic distortion plus noise (THDN). Digital data words are read into the at eight times the standard compact disk audio sampling frequency of.khz (.khz) so that a sine wave output of 99Hz is realized. For production testing, the output of the DAC goes to an I to V converter, then to a programmable gain amplifier to provide gain at lower signal output test levels, and then through a 0kHz low pass filter before being fed into an analog type distortion analyzer. Figure shows a block diagram of the production THDN test setup. For the audio bandwidth, THDN of the is essentially flat for all frequencies. The typical performance curve, THDN vs Frequency, shows four different output signal levels: 0dB, 0dB, 0dB, and 0dB. The test signals are derived from a special compact test disk (the CBS CD-). It is interesting to note that the 0dB signal falls only about 0dB below the full scale signal instead of the expected 0dB. This is primarily due to the superior low-level signal performance of the dual-dac Colinear architecture of the. In terms of signal measurement, THDN is the ratio of Distortion RMS Noise RMS / Signal RMS expressed in db. For the, THDN is 00% tested at all three specified output levels using the test setup shown in Figure. It is significant to note that this test setup does not include any output deglitching circuitry. All specifications are achieved without the use of external deglitchers. Dynamic Range Dynamic range in audio converters is specified as the measure of THDN at an effective output signal level of 0dB referred to 0dB. Resolution is commonly used as a theoretical measure of dynamic range, but it does not take into account the effects of distortion and noise at low signal levels. The INPUT CODE LOWER DAC CODE UPPER DAC CODE ANALOG OUTPUT (0-bit Binary Two s Complement) (9-bit Straight Binary) (9-bit Straight Binary) Full Scale LSB*... Full Scale LSB LSB*...0 Bipolar Zero LSB LSB* Bipolar Zero LSB LSB* Bipolar Zero LSB* Bipolar Zero LSB Bipolar Zero LSB Full Scale LSB Full Scale *The extra weight of LSB is added at this point to make the transfer function symmetrical around bipolar zero. TABLE I. Binary Two s Complement to Colinear Conversion Chart.

6 Use 00Hz High-Pass Filter and 0kHz Low-Pass Filter Meter Settings Distortion Analyzer Programmable Gain Amp 0dB to 0dB Low-Pass Filter 0kHz rd Order GIC Type (Shiba Soku Model or Equivalent) Binary Counter Digital Code (EPROM) Parallel-to-Serial Conversion DUT () I to V Converter OPA Clock Latch Enable Timing Logic Sampling Rate =.khz x (.khz) Output Frequency = 99Hz FIGURE. Production THDN Test Setup. Colinear architecture of the, with its ideal performance around bipolar zero, provides a more usable dynamic range, even using the strict audio definition, than any previously available D/A converter. Level Linearity Deviation from ideal versus actual signal level is sometimes called level linearity in digital audio converter testing. See the 90dB Signal Spectrum plot in the Typical Performance Curves section for the power spectrum of a at a 90dB output level. (The 90dB Signal plot shows the actual 90dB output of the DAC). The deviation from ideal for at this signal level is typically less than ±0.dB. For the 0dB Signal plot in the Typical Performance Curves section, true 0-bit digital code is used to generate a 0dB output signal. This type of performance is possible only with the low-noise, near-theoretical performance around bipolar zero of the s Colinear DAC circuitry. A commonly tested digital audio parameter is the amount of deviation from ideal of a khz signal when its amplitude is decreased from 0dB to 0dB. A digitally dithered input signal is applied to reach effective output levels of 0dB using only the available -bit code from a special compact disk test input. See the -Bit Level Linearity plot in the Typical Performance Curves section for the results of a tested using this -bit dithered fade-to-noise signal. Note the very small deviation from ideal as the signal goes from 0dB to 00dB. DC SPECIFICATIONS Idle Channel SNR Another appropriate specification for a digital audio converter is idle channel signal-to-noise ratio (idle channel SNR). This is the ratio of the noise on the DAC output at bipolar zero in relation to the full scale range of the DAC. To make this measurement, the digital input is continuously fed the code for bipolar zero while the output of the DAC is band-limited from 0Hz to 0kHz and an A-weighted filter is applied. The idle channel SNR for the is typically greater than 0dB, making it ideal for low-noise applications. Monotonicity Because of the unique dual-dac Colinear architecture of the, increasing values of digital input will always result in increasing values of DAC output as the signal moves away from bipolar zero in one-lsb steps (in either direction). The -Bit Monotonicity plot in the Typical Performance Curves section was generated using -bit digital code from a test compact disk. The test starts with 0 periods of bipolar zero. Next are 0 periods of alternating LSBs above and below zero, and then 0 periods of alternating LSBs above and below zero, and so on until 0LSBs above and below zero are reached. The signal pattern then begins again at bipolar zero. With, the low-noise steps are clearly defined and increase in near-perfect proportion. This performance is achieved without any external adjustments. By contrast, sigma-delta ( Bitstream, MASH, or -bit DAC) architectures are too noisy to even see the first or bits change (at bits), other than by a change in the noise level. Absolute Linearity Even though absolute integral and differential linearity specs are not given for the, the extremely low THDN performance is typically indicative of -bit to -bit integral linearity in the DAC, depending on the grade specified. The relationship between THDN and linearity, however, is not such that an absolute linearity specification for every individual output code can be guaranteed.

7 Offset, Gain, And Temperature Drift Although the is primarily meant for use in dynamic applications, specifications are also given for more traditional DC parameters such as gain error, bipolar zero offset error, and temperature gain and offset drift. DIGITAL INPUT Timing Considerations The accepts TTL compatible logic input levels. Noise immunity is enhanced by the use of differential current mode logic input architectures on all input signal lines. The data format of the is binary two s complement (BTC) with the most significant bit (MSB) being first in the serial input bit stream. Table II describes the exact relationship of input data to voltage output coding. Any number of bits can precede the 0 bits to be loaded, since only the last 0 will be transferred to the parallel DAC register after LE (P0, Latch Enable) has gone low. All DAC serial input data (P, DATA) bit transfers are triggered on positive clock (P, CLK) edges. The serial-toparallel data transfer to the DAC occurs on the falling edge of Latch Enable (P0, LE). The change in the output of the DAC coincides with the falling edge of Latch Enable (P0, LE). Refer to Figure for graphical relationships of these signals. Maximum Clock Rate A typical clock rate of.9mhz for the is derived by multiplying the standard audio sample rate of.khz by sixteen times (x oversampling) the standard audio word bit length of bits (.khz x x =.9MHz). Note that this clock rate accommodates a -bit word length, even though only 0 bits are actually being used. The maximum clock rate of MHz is guaranteed, but is not 00% final tested. The setup and hold timing relationships are shown in Figure. Stopped Clock Operation The is normally operated with a continuous clock input signal. If the clock is to be stopped between input data words, the last 0 bits shifted in are not actually shifted from the serial register to the latched parallel DAC register until Latch Enable (LE, P0) goes low. Latch Enable must remain low until after the first clock cycle of the next data word to insure proper DAC operation. In any case, the setup and hold times for Data and LE must be observed as shown in Figure. Data Input Clock Input Latch Enable >0ns LSB >0ns >0ns >ns >ns >ns >One Clock Cycle >ns >0ns MSB >One Clock Cycle FIGURE. Setup and Hold Timing Diagram. VOLTAGE OUTPUT DIGITAL INPUT ANALOG OUTPUT CURRENT OUTPUT (With External Op Amp),0,LSBs Full Scale Range mA V LSB NA.9nA.090µV FFFF HEX Full Scale mA.99999V HEX Bipolar Zero mA V FFFFF HEX Bipolar Zero LSB mA V 0000 HEX Full Scale mA V TABLE II. Digital Input/Output Relationships. P (Clock) P (Data) 9 0 MSB LSB P0 (Latch Enable) P (I OUT ) NOTES: () If clock is stopped between input of 0-bit data words, Latch Enable (LE) must remain low until after the first clock cycle of the next 0-bit data word stream. () Data format is binary two s complement (BTC). Individual data bits are clocked in on the corresponding positive clock edge. () Latch Enable (LE) must remain low at least one clock cycle after going negative. () Latch Enable (LE) must be high for at least one clock cycle before going negative. () I OUT changes on negative going edge of Latch Enable (LE). FIGURE. Timing Diagram.

8 INSTALLATION POWER SUPPLIES Refer to Figure for proper connection of the in the voltage-out mode using the internal feedback resistor. The feedback resistor connections (P9 and P0) should be left open if not used. The only requires a ±V supply. Both positive supplies should be tied together at a single point. Similarly, both negative supplies should be connected together. No real advantage is gained by using separate analog and digital supplies. It is more important that both these supplies be as clean as possible to reduce coupling of supply noise to the output. Power supply decoupling capacitors should be used at each supply pin to maximize power supply rejection, as shown in Figure, regardless of how good the supplies are. Both commons should be connected to an analog ground plane as close to the as possible. FILTER CAPACITOR REQUIREMENTS As shown in Figure, various size decoupling capacitors can be used, with no special tolerances being required. The size of the offset decoupling capacitor is not critical either, with larger values (up to 00µF) giving slightly better SNR readings. All capacitors should be as close to the appropriate pins of the as possible to reduce noise pickup from surrounding circuitry. MSB ADJUSTMENT CIRCUITRY Near optimum performance can be maintained at all signal levels without using the optional MSB adjust circuitry of the shown in Figure. Adjustability is provided for those cases where slightly better full-scale THDN is desired. Use of the MSB adjustments will only affect larger dynamic signals (between 0dB and db). This improvement comes from bettering the gain match between the upper and lower DACs at these signal levels. The change is realized by small adjustments in the bit- weights of each DAC. Great care should be taken, however, as improper adjustment will easily result in degraded performance. In theory, the adjustments would seem very simple to perform, but in practice they are actually quite complex. The first step in the theoretical procedure would involve making each bit- weight ideal in relation to its code minus one value (adjusting each potentiometer for zero differential nonlinearity error at the bit- major carries). This would be the starting point of each 00kΩ potentiometer for the next adjustment. Then, each potentiometer would be adjusted equally, in opposite directions, to achieve the lowest fullscale THDN possible (reversing the direction of rotation V A V POT LB Adj UB Adj 0kΩ 0kΩ 00kΩ 00kΩ FIGURE. Optional Bit- Adjustment Circuitry. V CAP V A V V A CAP ±V / OPA0 CAP BPO IOUT ACOM V POT LB Adj UB Adj DATA 9 RF LE 0 0 RF 9 V D DCOM CLK V D FIGURE. Connection Diagram.

9 for both if no immediate improvement were noted). This procedure would require the generation of the digital bit- major carry code to the input of the and a DVM or oscilloscope capable of reading the output voltage for a one LSB step (.µv) in addition to a distortion analyzer. A more practical approach would be to forego the minor correction for the bit- major carry adjustment and only adjust for upper and lower DAC gain matching. The problem is that just by connecting the MSB circuitry to the, the odds are that the upper and lower bit- weights would be greatly changed from their unadjusted states and thereby adversely affect the desired gain adjustment. Just centering the 00kΩ potentiometers would not necessarily provide the correct starting point. To guarantee that each 00kΩ potentiometer would be set to the correct starting or null point (no current into or out of the MSB adjust pins), the voltage drop across each corresponding 0kΩ resistor would have to measure 0V. A voltage drop of ±.mv across either 0kΩ resistor would correspond to a ±LSB change in the null point from its unadjusted state (LSB in current or.na x 0kΩ =.mv). Once these starting points for each potentiometer had been set, each potentiometer would then be adjusted equally, in opposite directions, to achieve the lowest full-scale THDN possible. If no immediate improvement were noted, the direction of rotation for both potentiometers would be reversed. One direction of potentiometer counter-rotations would only make the gain mismatch and resulting THDN worse, while the opposite would gradually improve and then worsen the THDN after passing through a no mismatch point. The determination of the correct starting direction would be arbitrary. This procedure still requires a good DVM in addition to a distortion analyzer. Each user will have to determine if a small improvement in full-scale THDN for their application is worth the expense of performing a proper MSB adjustment. APPLICATIONS The most common application for the is in highperformance and professional digital audio playback, such as in CD and DAT players. The circuit in Figure shows the in a typical combination with a digital interface format receiver chip (Yamaha YM), an x interpolating digital filter (Burr-Brown DF00P), and two third-order low-pass anti-imaging filters (implemented using Burr-Brown OPA0APs). Using an x digital filter increases the number of samples to the DAC by a factor of, thereby reducing the need for a higher order reconstruction or anti-imaging analog filter on the DAC output. An analog filter can now be constructed using a simple phase-linear GIC (generalized immittance converter) architecture. Excellent sonic performance is achieved using a digital filter in the design, while reducing overall circuit complexity at the same time. Because of its superior low-level performance, the is also ideally suited for other high-performance applications such as direct digital synthesis (DDS). 9

10 Interleaved Digital Input 0pF V.9MHz (9F S ) MΩ 0pF V.kΩ Digital Interface Format Receiver φ A BCO L/R DA Yamaha YM 0Ω 00pF V V X Interpolation Digital Filter 0-Bit D/A Converter DOR DATA BCO CLK WCK DOL 0 LE 0 Burr-Brown DF00P Burr-Brown 9 00pF 0 V V 0-Bit D/A Converter DATA CLK 0 LE 0 Burr-Brown 9 V A A A A V.9kΩ.kΩ.kΩ.kΩ V A 000pF A V ±V V OUT Right 000pF V.kΩ 000pF V.9kΩ.kΩ.kΩ.kΩ V A 000pF V A ±V V OUT Left 000pF V.kΩ 000pF A, A, A, A = Burr-Brown OPA0AP, or equivalent. FIGURE. Stereo Audio Application. 0

11 PACKAGE DRAWING