KT2001 KENTECH LABS, INC. POINT SOURCE AUDIO SPEAKER PROCESSING CIRCUIT Features • • • • Compact implementation of Point Source Audio Technology Supply Voltage from 5V to 12V Bipolar Technology for Low Noise Small 16-pin SOIC Package Applications • • • 16-pin 150mil wide SOIC PC Multimedia Speaker Systems Home Theater Systems Car Audio Description The KT2001 Point Source Processing Circuit provides a compact way to implement a point source speaker system. It is designed to operate with either a dual supplies or a single supply voltage; an internal reference voltage source generates a reference at half of the supply voltage. The chip is fabricated with a bipolar process that yields low noise while allowing a wide supply voltage range (5V to 12V). Typical Application Diagram 27nF 12K +12V 2.2µF Left Input 2.2µF Right Input 14 16 18K 12 1 V SF1 CCP 13 V CC 15 LIN Power Amplifiers 11 SF2 SF3 CTROUT 7 KT2001 12K RIN CTRIN 6 GND SUMOUT 8 LOUT 10 ROUT 9 2 V REF 47µF 5 Point-Source Satellite Speaker Unit SUBIN 12K 4.7nF Subwoofer SUBOUT 3 4 27K 12nF 27K 27K 27nF KT2001 Data Sheet (Preliminary) June 2002 This document pertains to a new product. Characteristic data and other specifications are subject to change without notice KT2001 Data Sheet June 2002 Absolute Maximum Ratings VCC Supply Voltage Input Voltage Current Into Any Pin Power Dissipation Storage Temperature Range 20V -0.3V to VCC+0.3V ± 50mA 500mW -55°C to 125°C Recommended Operating Conditions Parameter VCC Supply Voltage Operating Temperature Range Conditions Min 4.75 0 Typ Max 12 70 Units V °C Electrical Characteristics (at TA = 25ºC and 5V ≤ VCC ≤ 12V unless otherwise noted) Parameter Input Impedance (LIN, RIN) Conditions Min 35K Output Voltage Range Output Impedance Typ 50K 0.5 Max 65K Units Ω VCC-1 10 V Ω 6K Ω LIN, RIN = 1.0VRMS, fIN=10kHz LIN, RIN = 1.0VRMS, fIN=100Hz LIN, RIN = 1.0VRMS, fIN=100Hz 0.025 0.05 0.05 % % % Signal to Noise Ratio (A-weighted) LIN, RIN = 0VRMS, measured at LOUT, ROUT, CTROUT or SUBOUT 105 dB Power Supply Current VCC=12V, no input signal 17.0 VREF Input Impedance Total Harmonic Distortion (THD) LOUT, ROUT CTROUT SUBOUT TBD mA All Specifications are subject to change without notice. KENTECH LABS, INC. 2 June 2002 KT2001 Data Sheet VCCP 1 16 RIN VREF 2 15 LIN SUBOUT 3 14 SF1 SUBIN 4 13 VCC SUMOUT 5 12 SF2 CTRIN 6 11 SF3 CTROUT 7 10 LOUT GND 8 9 ROUT Pin Connection Diagram Small-Outline Package Description of Pin Functions Name LIN RIN LOUT ROUT CTROUT SUBOUT SUMOUT CTRIN SUBIN SF1 SF2 SF3 VREF Pin 15 16 10 9 7 3 5 6 4 14 12 11 2 VCCP, VCC GND 1,13 8 Function Left channel input. Has a 50K nominal input impedance Right channel input. Has a 50K nominal input impedance Left channel satellite speaker output. Right channel satellite speaker output. Center channel satellite speaker output. Subwoofer speaker output. Inverted sum of LIN and RIN channels. Should be used to drive CTRIN and SUBIN inputs. Center channel amp inverting input. Should be connected to feedback network and SUMOUT. Subwoofer channel amp inverting input. Should be connected to feedback network and SUMOUT. Side channel filter network pin 1. See application notes for usage Side channel filter network pin 2. See application notes for usage Side channel filter network pin 3. See application notes for usage VREF signal reference input. Should be filtered to ground in single supply applications or connected to ground for dual supplies Positive supply pins. Should be externally tied together. Supply ground for single supply or negative supply for dual supply Fundamentals of Operation The KT2001 is designed to act as a specialized low-level crossover circuit for a single three-speaker satellite unit and a conventional subwoofer. The CTROUT and SUBOUT components only depend on the sum of the left and right channels. The KT2001 provides an intermediate output that is as follows: SUM OUT = − ( 1 L IN + R IN 2 ) The CTROUT and SUBOUT outputs are each generated by an undedicated inverting op-amp with inputs CTRIN and SUBIN respectively. The CTROUT op-amp is designed to provide a single-pole low-pass filter (acting as an inverting integrator) to generate the center speaker signal. The SUBOUT op-amp is designed to provide a two-pole low-pass filter to generate the subwoofer speaker signal. The LOUT and ROUT outputs are largely a function of the difference between KENTECH LABS, INC. 3 KT2001 Data Sheet June 2002 the left and right channel inputs (the side signal). This difference or side signal is filtered by a side filter network connected to the SF1, SF2 and SF3 pins, and then is combined with the sum components as follows: L IN + R IN 1 Z − CTR OUT + (L IN − R IN ) + 2 2 Z 2 1 L OUT = L IN + R IN 1 Z − CTR OUT + (R IN − L IN ) + 2 2 Z 2 1 R OUT = where the impedances Z1 and Z2 are as shown in Figure 1. The side filter network aids speaker crosstalk cancellation in the bass to low midrange frequencies and can also be used to equalize the speaker response in the high treble frequencies. Z1 14 VCCP VCC SF1 Z2 12 SF2 KT2001 11 SF3 LOUT ROUT Figure 1. General Side Filter Network Application Notes A typical application circuit is shown in Figure 2. The component values shown in Figure 2 are representative of those in a typical circuit, but many values need to be chosen in conjunction with the choice of speaker drivers and the design of their respective enclosures. As in most conventional multi-way systems, the subwoofer and satellite speakers operate in mutually exclusive frequency bands. The KT2001 is designed to use second-order Linkwitz-Riley crossover target functions. Since the point source system benefits from having the lowest possible crossover frequency, the satellite driver’s natural 12dB/octave roll-off below resonance is used. The subwoofer crossover function should be tuned to this resonance. To provide a flat crossover it is important to follow a couple basic guidelines: 1. 2. The satellite drivers and the enclosure should be designed to have a QES as close to 0.5 as possible (critically damped). The satellite drivers need to be connected out-of-phase with respect to the subwoofer speaker. (The KT2001 does not provide this function internally.) While the KT2001 nominally provides identical passband gains for each output channel, these will need to be different depending on the speaker efficiency and other design parameters. In general, the center channel will need to be attenuated compared to the side (left and right) output channels. Many applications might require a separate volume control on the subwoofer channel too. The output AC coupling capacitors C8 through C10 shown in Figure 2 can be used in conjunction with resistors R8 through R10 to attenuate bass frequency power to the satellite speakers below the critical portion of the crossover frequency band. KENTECH LABS, INC. 4 June 2002 KT2001 Data Sheet C2 27nF R1 12K +12V Left Input C6 2.2µF VCCP 13 VCC 15 LIN 16 Right Input C7 2.2µF 2 C1 47µF R2 18K 14 1 C8 0.1µF 12 SF3 KT2001 RIN 8 5 SUBIN R3 12K Power Amplifier Subwoofer C9 0.1µF 10 LOUT 9 ROUT 7 CTROUT CTRIN 6 VREF GND SUMOUT Point Source Satellite Speaker Unit 11 SF2 SF1 Power Amplifiers SUBOUT 3 R4 12K C3 4.7nF C10 0.1µF R10 15K R9 15K R8 15K 4 R5 27K C5 12nF R6 27K R7 27K C4 27nF Figure 2. Typical Application Circuit Subwoofer Filter Design The Laplace transfer function of the second order filter shown in Figure 2 is as follows: SUB OUT A =− , SUM OUT 1 + sC 5 (R7 + R6 (1 + A)) + s 2 R6 R7 C 4 C 5 where the passband gain is defined as: A≡ R7 R5 The Linkwitz-Riley target function requires a double-pole at or near the satellite speaker driver resonant frequency: f0 = 1 2π R6 R7 C 4 C 5 KENTECH LABS, INC. 5 KT2001 Data Sheet June 2002 While the circuit shown in Figure 2 assumes a passband gain of one, other values are possible. To choose component values, after choosing the passband gain, the ratio of the capacitances is restricted as follows (based on the doublepole constraint): C4 ≥ 1+ A C5 Since the range of standard capacitor values are more limited than the typical range of resistor values, it is often easiest to choose a ratio of capacitors first and then determine the following resistor ratio: R7 C C C = 2 4 − (1 + A) − 2 4 4 − (1 + A) R6 C5 C5 C5 The actual component values can be chosen by using the following relationship: 1 2πf 0 R6 C 4 = C4 C5 R7 R6 The ratios can be used to determine the remaining components as follows: C5 = C4 C4 C5 , R R7 = R6 7 R6 , R5 = R7 A It may be necessary to iterate the process to find a close match with standard values. There are a couple of convenient simplifications in special cases. For instance: If R C4 = 1 + A , then 7 = 1 + A too. C5 R6 For A=1, there is a convenient ratio with C4 = 27nF and C5=12nF (as shown in Figure 2.) This implies that R5=R6=R7. In this special case: R5 = R6 = R7 = 3 4πf 0 (27 nF ) Center Filter Design Since the CTROUT output is used internally to the KT2001 to generate the LOUT and ROUT signals, the gain of the center filter should always be one. That is: R3 = R4 For the simple integrator shown, the center/side crossover frequency is: f CC = 1 2πR4 C 3 KENTECH LABS, INC. 6 June 2002 KT2001 Data Sheet This frequency should be chosen empirically. Typically it will be in the high-treble range (>5KHz). Many applications will benefit if C3 is simply absent. Side Filter Design For the side filter network shown in Figure 2, the overall side or difference signal transfer function is: 1 R 1 Z 2 1 R2 1 + = + = + 2 2 Z 1 2 R1 1 + sR2 C 2 2 R1 R1 R2 C2 R1 + 2 R2 1 + sR2 C 2 1+ s It is probably best to keep the pole of the function at or above the satellite resonant frequency: f0 ≤ 1 2πR2 C 2 And it probably is best to keep the zero of the function below 1KHz or so: 1KHz ≥ 1 R1 R2 2π C2 R1 + 2 R2 Input Bypass Capacitors Since the DC signal levels will be biased at the VREF level, many applications will require AC coupling capacitors on the input and/or the output. The input capacitors should be chosen based on the desired roll-off frequency in conjunction with the nominal input impedance of 50KΩ (0.47µF is the recommended minimum value for these input capacitors). Power Supplies The KT2001 is designed to operate with a single 5V to 12V supply or dual ±2.5V to ±6V supplies. Proper bypassing of these supplies is important to ensure low noise and proper function of the chip. The input signal DC reference level is established by the VREF input pin (nominally VCC /2 - 0.3V). This pin can be tied to ground for dual supply operation. When operating with a single supply, the VREF pin should be bypassed to ground with a 10-100µF capacitor. Larger values of this capacitor generally improve power supply noise rejection. If another low-impedance ground reference is available, the pin VREF can be tied to it. The VREF pin has a relatively high impedance; as a consequence, it cannot be used to supply much current without additional buffering. KENTECH LABS, INC. 7 KT 2001 Data Sheet June 2002 KT 2001 FUNCTIONALITY TESTING (KT2001) Test Description Setup: SF1-3 Not engaged; Center and subwoofer op amps not driven by Sum Out; Vcc = 12V; TA = 20° C Test Test Name Nom Value DESCRIPTION 1 ICC 15MA Supply Current 2 VREF 5.67V Reference voltage for all internal and external inputs 3-14 V RBUF ± 10MV DC quiescent values re VREF for all inputs and outputs V FLT IN/OUT V SUM OUT V SUB IN/OUT V CTR IN/OUT V LOUT V ROUT 15-16 GN L-SUM -0.5 Gain from Left and Right inputs to SUM output with ± 1V applied to inputs GN R-SUM 17 GN L-LO +1.0 18 GN L-RO ± 20MV 19 GN R-RO +1.0 20 CTR OA ± 10MV 21-22 CTR-LO +1.0 Gain from Lin to Lout with ± 1V applied to input Crosstalk from Lin to Rout; this due to incomplete cancellation of signals and effectively measures gain matching Gain from Rin to Rout with ± 1V applied to input Center op amp summing node R with ± 100 UA applied. Effectivly measures op amp gain for ± 2V output swing Gain from Center out to Left and Right outputs at ± 1V CTR-RO 23-24 SUB OA ± 10MV Filter and Sub op amp summing node R with ± 100 UA applied and ± 2V output swing RBUF VP+ 10.5V Right buffer max. high and min. low output with 11.7 / 0.3V applied to input and 0.5 MA sink/source at output RBUF VP- .35V 27 SF3 VP+ 10.5V Filter max. high output with - 0.3 MA applied to input 28 LO VP+ 10.5V Left max. high output with Filter at max high and additional -2V from Center out; 2MA sink at left out 29 SF3 VP- .35V Filter min. low output with +0.3 MA at input 30 LO VP- .45V Left min. low output with Filter at min. low and additional +2V from Center out; 1MA source at left out 32-33 LBUF VP+ ± .1V Left buffer max. high and min. low output with 11.7 / 0.3V applied to input as measured through and compared to Filter output FLT OA 25-26 LBUF VP34-35 37,39 40-41 43-44 31,36,38,45 46-47 Neg. value means buffer output / filter CM input swing is limiting factor SUM VP+ 10.5V RO VP- .4V and 1MA source on Right out. SUM VP- .60V Sum min. low and Right max. high outputs with 11.7V applied to both Left and Right inputs and with .75MA source on Sum out RO VP+ 10.5V and 2MA sink on Right out. CTR VP+ 10.5V Center max. high and min. low output with ± .6MA applied to input and with 2MA sink and .6MA source on its ouput CTR VP- .5V SUB VP+ 10.5V SUB VP- .5V LO IL 1.3MA RO IL 1.3MA SUM IL .9MA SUB IL 1.3MA L RIN 50K R RIN 50K Sum max. high and Right min. low ouputs with 11.7 / 0.3V applied to both Left and Right inputs and with 2MA sink on Sum out Sub max. high and min. low output with ± .3MA applied to its input and 2MA sink and with .75MA source on its ouput Output sink capability of Left, Right, Sum, and Sub ouputs Left and right inputs resistance measured by increasing inputs 4V above quiescent and measuring input current KENTECH LABS, INC. 8 June 2002 KT2001 Data Sheet Notes KENTECH LABS, INC. 9 KT2001 Data Sheet June 2002 The information furnished in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Kentech Labs, Inc. for its use, nor for any infringements of patents or other rights of third parties which may result from its use. This document is the property of Kentech Labs, Inc. and implies no license under patents, copyrights, trademarks, or trade secrets. Copyright © Kentech Labs, Inc. 2002 (All Rights Reserved) For more information about Point Source audio technology please visit our website at www.kentechlabs.com. KENTECH LABS, INC. 2010 North First Street, Suite 403 San Jose, CA 95131 ph 408.894.1565 fax 408.894.8116 KENTECH LABS, INC. 10