AN142AN142, ►Elektronika, ►Aplikacje
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INTEGRATED CIRCUITS AN142 Audio circuits using the NE5532/3/4 author 1984 Oct Philips Semiconductors Application note Audio circuits using the NE5532/3/4 AN142 AUDIO CIRCUITS USING THE NE5532/33/34 The following will explain some of Philips Semiconductors low noise op amps and show their use in some audio applications. actually five individual active filters with the same feedback design for all five. The main difference in all five stages is the values of C5 and C6, which are responsible for setting the center frequency of each stage. Linear pots are recommended for R9. To simplify use of this circuit, a component value table is provided, which lists center frequencies and their associated capacitor values. Notice that C5 equals (10) C6, and that the Value of R8 and R10 are related to R9 by a factor of 10 as well. The values listed in the table are common and easily found standard values. DESCRIPTION The 5532 is a dual high-performance low noise operational amplifier. Compared to most of the standard operational amplifiers, such as the 1458, it shows better noise performance, improved output drive capability and considerably higher small-signal and power bandwidths. This makes the device especially suitable for application in high quality and professional audio equipment, instrumentation and control circuits, and telephone channel amplifiers. The op amp is internally-compensated for gains equal to one. If very low noise is of prime importance, it is recommended that the 5532A version be used which has guaranteed noise voltage specifications. RIAA EQUALIZATION AUDIO PREAMPLIFIER USING NE5532A With the onset of new recording techniques with sophisticated playback equipment, a new breed of low noise operational amplifiers was developed to complement the state-of-the-art in audio reproduction. The first ultra-low noise op amp introduced by Philips Semiconductors was called the NE5534A. This is a single operational amplifier with less than 4nV/ / Hz input noise voltage. The NE5534A is internally-compensated at a gain of three. This device has been used in many audio preamp and equalizer (active filter) applications since its introduction early last year. Many of the amplifiers that are being designed today are DC-coupled. This means that very low frequencies (2-15Hz) are being amplified. These low frequencies are common to turntables because of rumble and tone arm resonances. Since the amplifiers can reproduce these sub-audible tones, they become quite objectionable because the speakers try to reproduce these tones. This causes non-linearities when the actual recorded material is amplified and converted to sound waves. The RIAA has proposed a change in its standard playback response curve in order to alleviate some of the problems that were previously discussed. The changes occur primarily at the low frequency range with a slight modification to the high frequency range (See Figure 2). Note that the response peak for the bass section of the playback curve now occurs at 31.5Hz and begins to roll off below that frequency. The roll-off occurs by introducing a fourth RC network with a 7950 m s time constant to the three existing networks that make up the equalization circuit. The high end of the equalization curve is extended to 20kHz, because recordings at these frequencies are achievable on many current discs. APPLICATIONS The Philips Semiconductors 5532 High-Performance Op Amp is an ideal amplifier for use in high quality and professional audio equipment which requires low noise and low distortion. The circuit included in this application note has been assembled on a PC board, and tested with actual audio input devices (Tuner and Turntable). It consists of an RIAA (Recording Industry Association of America) preamp, input buffer, 5-band equalizer, and mixer. Although the circuit design is not new, its performance using the 5532 has been improved. The RIAA preamp section is a standard compensation configuration with low frequency boost provided by the Magnetic cartridge and the RC network in the op amp feedback loop. Cartridge loading is accomplished via R1. 47k was chosen as a typical value, and may differ from cartridge to cartridge. The Equalizer section consists of an input buffer, 5 active variable band pass/notch (depending on R9’s setting) filters, and an output summing amplifier. The input buffer is a standard unity gain design providing impedance matching between the preamplifier and the equalizer section. Because the 5532 is internally-compensated, no external compensation is required. The 5-band active filter section is C5 Equ In 5 RIAA Out + RIAA C1 3 7 R7 R8 R7 + 1/2 5532 1 R5 6 – 1/2 5532 R1 2 – R5 R9 C6 R9 R11 R2 R3 2 – 1/2 5532 + C7 1 R10 6 FLAT C2 C3 – 1/2 5532 TO VOL./ BAL AMP 3 7 + 5 + EQUALIZE R4 C4 REPEAT ABOVE CIRCUIT FOR DESIRE NO. OF STAGES. R12 SL00850 Figure 1. RIAA - Equalizer Schematic 1984 Oct 2 August 1988 Rev: 2 Philips Semiconductors Application note Audio circuits using the NE5532/3/4 AN142 COMPONENT VALUES FOR FIGURE 1 R8=25k R7=2.4k R9=240k R8=50k R7=5.1k R9=510k R8=100k R7=10k R9=1meg f O C5 C6 f O C5 C6 f O C5 C6 23Hz 1 m F 0.1 m F 25Hz 0.47 m F 0.047 m F 12Hz 0.47 m F 0.047 m F 50Hz 0.47 m F 0.047 m F 36Hz 0.33 m F 0.033 m F 18Hz 0.33 m F 0.033 m F 72Hz 0.33 m F 0.033 m F 54Hz 0.22 m F 0.022 m F 27Hz 0.22 m F 0.022 m F 108Hz 0.22 m F 0.022 m F 79Hz 0.15 m F 0.015 m F 39Hz 0.15 m F 0.015 m F 158Hz 0.15 m F 0.015 m F 119Hz 0.1 m F 0.01 m F 59Hz 0.1 m F 0.01 m F 238Hz 0.1 m F 0.01 m F 145Hz 0.082 m F 0.0082 m F 72Hz 0.082 m F 0.0082 m F 290Hz 0.082 m F 0.0082 m F 175Hz 0.068 m F 0.0068 m F 87Hz 0.068 m F 0.0068 m F 350Hz 0.068 m F 0.0068 m F 212Hz 0.056 m F 0.0056 m F 106Hz 0.056 m F 0.0056 m F 425Hz 0.056 m F 0.0056 m F 253Hz 0.047 m F 0.0047 m F 126Hz 0.047 m F 0.0047 m F 506Hz 0.047 m F 0.0047 m F 360Hz 0.033 m F 0.0033 m F 180Hz 0.033 m F 0.0033 m F 721Hz 0.033 m F 0.0033 m F 541Hz 0.022 m F 0.0022 m F 270Hz 0.022 m F 0.0022 m F 1082Hz 0.022 m F 0.0022 m F 794Hz 0.015 m F 0.0015 m F 397Hz 0.015 m F 0.0015 m F 1588Hz 0.015 m F 0.0015 m F 1191Hz 0.01 m F 0.001 m F 595Hz 0.01 m F 0.001 m F 2382Hz 0.01 m F 0.001 m F 1452Hz 0.0082 m F 820pF 726Hz 0.0082 m F 820pF 2904Hz 0.0082 m F 820pF 1751Hz 0.0068 m F 680pF 875Hz 0.0068 m F 680pF 3502Hz 0.0068 m F 680pF 2126Hz 0.0056 m F 560pF 1063Hz 0.0056 m F 560pF 4253Hz 0.0056 m F 560pF 2534Hz 0.0047 m F 470pF 1267Hz 0.0047 m F 470pF 5068Hz 0.0047 m F 470pF 3609Hz 0.0033 m F 330pF 1804Hz 0.0033 m F 330pF 7218Hz 0.0033 m F 330pF 5413Hz 0.0022 m F 220pF 2706Hz 0.0022 m F 220pF 10827Hz 0.0022 m F 220pF 7940Hz 0.0015 m F 150pF 3970Hz 0.0015 m F 150pF 15880Hz 0.0015 m F 150pF 11910Hz 0.001 m F 100pF 5955Hz 0.001 m F 100pF 23820Hz 0.001 m F 100pF 14524Hz 820pF 82pF 7262Hz 820pF 82pF 17514Hz 680pF 68pF 8757Hz 680pF 68pF 21267Hz 560pF 56pF 10633Hz 560pF 56pF 12670Hz 470pF 47pF 18045Hz 330pF 33pF –25 –20 OLD RIAA –15 –10 –5 NEW RIAA 0 (db) 5 10 15 20 25 30 1 10 100 (HZ) 1K 10K 100K SL00851 Figure 2. Proposed RIAA Playback Equalization 1984 Oct 3 Philips Semiconductors Application note Audio circuits using the NE5532/3/4 AN142 –15V .1 m F .27 m F – INPUT + 3 8 TO LOAD 47K NE5532A 1 2 4 + – .1 m F –15V 49.9K + SL00853 49.9 Figure 4. Assume a signal input square wave with dV/dt of 250V/ m s and 2V peak amplitude as shown. If a 22pF compensation capacitor is inserted and the R 1 C 1 circuit deleted, the device slew rate falls to approximately 7V/ m s. The input waveform will reach 2V/250V/ m s or 8ns, while the output will have changed (8 × 10 -3 ) only 56mV. The differential input signal is then (V IN -V O ) R I /R I +R F or approximately 1V. The diode limiter will definitely be active and output distortion will occur; therefore, V IN <1V as indicated. Next, a sine wave input is used with a similar circuit. The slew rate of the input waveform now depends on frequency and the exact expression is dv dt 2 cos t .056 m F 4.99K 47 m F .015 m F NOTE: All resistors are 1% metal film. SL00852 Figure 3. RIAA Phonograph Preamplifier Using the NE5532A NE5533/34 DESCRIPTION the 5533/5534 are dual and single high-performance low noise operational amplifiers. Compared to other operational amplifiers, such as TL083, they show better noise performance, improved output drive capability and considerably higher small-signal and power bandwidths. This makes the devices especially suitable for application in high quality and professional audio equipment, instrumentation and control circuits, and telephone channel amplifiers. The op amps are internally-compensated for gain equal to, or higher than, three. The frequency response can be optimized with an external compensation capacitor for various applications (unity gain amplifier, capacitive load, slew rate, low overshoot, etc.) If very low noise is of prime importance, it is recommended that the 5533A/5534A version be used which has guaranteed noise specifications. The upper limit before slew rate distortion occurs for small-signal (V IN <100mV) conditions is found by setting the slew rate to 7V/ m s. That is: 7 x 10 6 V s 2 cos t at w t = 0 LIMIT 7x10 6 2 3.5x10 6 rad s f LIMIT 3.5x10 6 2 560kHz APPLICATIONS Diode Protection of Input The input leads of the device are protected from differential transients above ± 0.6V by internal back-to-back diodes. Their presence imposes certain limitations on the amplifier dynamic characteristics related to closed-loop gain and slew rate. Consider the unity gain follower as an example: 1984 Oct 4 Philips Semiconductors Application note Audio circuits using the NE5532/3/4 AN142 dV/dt External Compensation Network Improves Bandwidth By using an external lead-lag network, the follower circuit slew rate and small-signal bandwidth can be increased. This may be useful in situations where a closed-loop gain less than 3 to 5 is indicated. A number of examples are shown in subsequent figures. The principle benefit of using the network approach is that the full slew rate and bandwidth of the device is retained, while impulse-related parameters such as damping and phase margin are controlled by choosing the appropriate circuit constants. For example, consider the following configuration: +2 –2V V IN = 2 Sin w t 1K 1K 22pF NE 5534 SL00854 Figure 5. R f 5 22pF Rj – 2 2V C C 0 8 R1 NE 5534 0 6 –V O C1 –V i 3 + D t 1 D t 2 SL00855 Figure 6. 1 GAIN 90 1K – R LAG NETWORK NE5534 45 C + SL00856 0 Figure 7. 0 0.1 1.0 10 50 MHz SL00857 Figure 8. 1984 Oct 5 [ Pobierz całość w formacie PDF ] |
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