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LTC1562IG-2

LTC1562IG-2

  • 厂商:

    LINEAR(凌力尔特)

  • 封装:

    SSOP20

  • 描述:

    LTC1562IG-2

  • 数据手册
  • 价格&库存
LTC1562IG-2 数据手册
LTC1562-2 Very Low Noise, Low Distortion Active RC Quad Universal Filter U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Continuous Time—No Clock Four 2nd Order Filter Sections, 20kHz to 300kHz Center Frequency Butterworth, Chebyshev, Elliptic or Equiripple Delay Response Lowpass, Bandpass, Highpass Responses 99dB Typical S/N, ±5V Supply (Q = 1) 93dB Typical S/N, Single 5V Supply (Q = 1) Rail-to-Rail Input and Output Voltages DC Accurate to 3mV (Typ) ±0.5% Typical Center Frequency Accuracy “Zero-Power” Shutdown Mode Single or Dual Supply, 5V to 10V Total Resistor-Programmable fO, Q, Gain The LTC®1562-2 is a low noise, low distortion continuous time filter with rail-to-rail inputs and outputs, optimized for a center frequency (fO) of 20kHz to 300kHz. Unlike most monolithic filters, no clock is needed. Four independent 2nd order filter blocks can be cascaded in any combination, such as one 8th order or two 4th order filters. Each block’s response is programmed with three external resistors for center frequency, Q and gain, using simple design formulas. Each 2nd order block provides lowpass and bandpass outputs. Highpass response is available if an external capacitor replaces one of the resistors. Allpass, notch and elliptic responses can also be realized. The LTC1562-2 is designed for applications where dynamic range is important. For example, by cascading 2nd order sections in pairs, the user can configure the IC as a dual 4th order Butterworth lowpass filter with 90dB signal-to-noise ratio from a single 5V power supply. Low level signals can exploit the built-in gain capability of the LTC1562-2. Varying the gain of a section can achieve a dynamic range as high as 114dB with a ±5V supply. Other cutoff frequency ranges can be provided upon request. Please contact LTC Marketing. U APPLICATIO S ■ ■ ■ ■ ■ High Resolution Systems (14 Bits to 18 Bits) Antialiasing/Reconstruction Filters Data Communications, Equalizers Dual or I-and-Q Channels (Two Matched 4th Order Filters in One Package) Linear Phase Filtering Replacing LC Filter Modules , LTC and LT are registered trademarks of Linear Technology Corporation. U ■ TYPICAL APPLICATIO Amplitude Response Dual 4th Order 200kHz Butterworth Lowpass Filter, SNR 96dB 10 RIN2 7.87k VIN1 1 RQ1 4.22k 2 R21 7.87k 3 5 5V 0.1µF R23 7.87k RQ3 4.22k RIN3 7.87k VIN2 *V – ALSO AT PINS 4, 7, 14 & 17 ALL RESISTORS 1% METAL FILM 6 8 9 10 INV B V1 B V2 B INV C V1 C V2 C –10 19 RQ2 10.2k 18 R22 7.87k 16 V+ LTC1562-2 V – 15 SHDN AGND 13 V2 A V2 D 12 V1 A V1 D 11 INV A INV D 0 VOUT1 20 –20 – 5V* 0.1µF GAIN (dB) RIN1 7.87k –30 –40 –50 R24 7.87k –60 RQ4 10.2k –70 –80 50k VOUT2 RIN4 7.87k 1562-2 TA01 1M 100k 1.5M FREQUENCY (Hz) 1562-2 TA02 15622fa 1 LTC1562-2 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) Total Supply Voltage (V + to V –) .............................. 11V Maximum Input Voltage at Any Pin ....................(V – – 0.3V) ≤ V ≤ (V + + 0.3V) Storage Temperature Range ................. – 65°C to 150°C Operating Temperature Range LTC1562C-2 ............................................ 0°C to 70°C LTC1562I-2 ........................................ – 40°C to 85°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW INV B V1 B V2 B V –* V+ SHDN V –* V2 A V1 A INV A 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 INV C V1 C V2 C V –* V– AGND V –* V2 D V1 D INV D LTC1562CG-2 LTC1562IG-2 G PACKAGE 20-LEAD PLASTIC SSOP *G PACKAGE PINS 4, 7, 14, 17 ARE SUBSTRATE/SHIELD CONNECTIONS AND MUST BE TIED TO V – TJMAX = 150°C, θJA = 136°C/W Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = ±5V, outputs unloaded, SHDN pin to logic “low”, unless otherwise noted. AC specs are for a single 2nd order section, RIN = R2 = 10.4k ±0.1%, RQ = 9.09k ±0.1%, fO = 175kHz. SYMBOL PARAMETER VS Total Supply Voltage IS Supply Current VOS HL CONDITIONS MIN TYP MAX 10.5 V 21 22.5 23.5 25 mA mA 28 30 mA mA 4.75 VS = ±2.375V, RL = 5k, CL = 30pF, Outputs at 0V VS = ±5V, RL = 5k, CL = 30pF, Outputs at 0V VS = ±2.375V, RL = 5k, CL = 30pF, Outputs at 0V VS = ±5V, RL = 5k, CL = 30pF, Outputs at 0V ● ● Output Voltage Swing, V2 Outputs VS = ±2.375V, RL = 5k, CL = 30pF VS = ±5V, RL = 5k, CL = 30pF ● ● Output Voltage Swing, V1 Outputs VS = ±2.375V, RL = 5k, CL = 30pF, f = 250kHz VS = ±5V, RL = 5k, CL = 30pF, f = 250kHz UNITS 4.2 9.3 4.6 9.8 VP-P VP-P 8.4 4.5 9.7 VP-P VP-P DC Offset Magnitude, V2 Outputs VS = ±2.375V, Input at AGND Voltage VS = ±5V, Input at AGND Voltage DC AGND Reference Point VS = Single 5V Supply 2.5 Center Frequency (f O) Error (Notes 2, 3) VS = ±5V, V2 Output Has RL = 5k, CL = 30pF 0.5 1.7 % Lowpass Passband Gain at V2 Output VS = ±2.375V, fIN = 10kHz, V2 Output Has RL = 5k, CL = 30pF + 0.05 + 0.1 dB Q Accuracy VS = ±2.375V, V2 Output Has RL = 5k, CL = 30pF +2 % Wideband Output Noise VS = ±2.375V, BW = 400kHz, Input AC GND VS = ±5V, BW = 400kHz, Input AC GND 39 39 µVRMS µVRMS Input-Referred Noise, Gain = 100 BW = 400kHz, f O = 200kHz, Q = 1, Input AC GND 7.3 µVRMS 3 3 ● 0 17 17 mV mV V 15622fa 2 LTC1562-2 ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = ±5V, outputs unloaded, SHDN pin to logic “low”, unless otherwise noted. AC specs are for a single 2nd order section, RIN = R2 = 10.4k ±0.1%, RQ = 9.09k ±0.1%, fO = 175kHz. SYMBOL PARAMETER CONDITIONS THD Total Harmonic Distortion, V2 Output fIN = 20kHz, 2.8VP-P, V1 and V2 Outputs Have RL = 5k, CL = 30pF – 100 dB fIN = 20kHz, 9VP-P, V1 and V2 Outputs Have RL = 5k, CL = 30pF – 82 dB SHDN Pin to V + SHDN Pin to V +, VS = ±2.375V 1.5 1.0 Shutdown Supply Current MIN Shutdown-Input Logic Threshold TYP MAX UNITS µA µA 15 2.5 V µA Shutdown-Input Bias Current SHDN Pin to 0V – 10 Shutdown Delay SHDN Pin Steps from 0V to V + 20 µs V + to 0V 100 µs 5 pA Shutdown Recovery Delay SHDN Pin Steps from Inverting Input Bias Current, Each Biquad Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: fO change from ±5V to ±2.375 supplies is – 0.2% typical, fO temperature coefficient magnitude, 25°C to 85°C, is 50ppm/°C typical. As with the LTC1562, fO decreases with increasing temperature. – 20 Note 3: Tighter frequency tolerance is available, consult factory. U W TYPICAL PERFOR A CE CHARACTERISTICS fO Error vs Nominal fO (VS = ±2.5V) fO Error vs Nominal fO (VS = ±5V) T = 25°C 2.5 RA = R IN Q 2.0 1.5 1.5 Q=5 0 – 0.5 –1.0 Q = 2.5 35 1.0 0.5 Q=5 0 – 0.5 –1.0 –2.0 Q=1 –2.5 –2.5 –3.0 120 140 160 180 200 220 240 260 280 NOMINAL fO (kHz) 1562-2 G01 TA = 70°C TA = 25°C RIN = RQ Q=5 30 Q = 2.5 25 20 15 10 –1.5 –1.5 –2.0 40 Q ERROR (%) 1.0 fO ERROR (%) fO ERROR (%) T = 25°C 2.5 RA = R IN Q 2.0 0.5 Q Error vs Nominal fO (VS = ±5V) 45 3.0 3.0 Q = 2.5 Q=1 5 Q=1 0 –3.0 120 140 160 180 200 220 240 260 280 NOMINAL fO (kHz) 1562-2 G02 –5 100 120 140 160 180 200 220 240 260 280 300 NOMINAL fO (kHz) 1562-2 G03 15622fa 3 LTC1562-2 U W TYPICAL PERFOR A CE CHARACTERISTICS 55 3.00 Q ERROR (%) 2.50 Q=5 30 25 Q = 2.5 15 10 RIN = RQ Q=5 2.25 35 20 TA = 70°C TA = 25°C 2.00 1.75 1.50 1.25 Q = 2.5 1.00 0.75 Q=1 5 0.50 0 0.25 –5 100 120 140 160 180 200 220 240 260 280 300 NOMINAL fO (kHz) Q=1 0 100 120 140 160 180 200 220 240 260 280 300 NOMINAL fO (kHz) 1562-2 G04 LP Noise vs Nominal fO (VS = ±5V, 25°C) (Figure 3, V2 Output) (RIN = R2) 90 80 80 BP NOISE (µVRMS) 90 Q=5 60 Q = 2.5 40 Distortion vs External Load Resistance and Frequency (VS = ±5V, 25°C) (Figure 8) Q=1 70 60 50 Q=5 Q = 2.5 40 Q=1 30 30 20 20 10 120 140 160 180 200 220 240 260 280 NOMINAL fO (kHz) 10 120 140 160 180 200 220 240 260 280 NOMINAL fO (kHz) 1562-2 G07 1562-2 G08 0 –10 –20 –30 100 2nd ORDER LOWPASS fO = 200kHz Q = 0.7 OUTPUT LEVEL 1VRMS (2.83VP-P) ± 5V SUPPLIES 10 – 40 1 – 50 – 60 0.1 –70 – 80 – 90 –100 10k fIN = 100kHz fIN = 50kHz 0.01 fIN = 20kHz 0.001 2k 5k EXTERNAL LOAD RESISTANCE (Ω) THD (AMPLITUDE BELOW FUNDAMENTAL) (%) 100 50 1562-2 G6 BP Noise vs Nominal fO (VS = ±5V, 25°C) (Figure 3, V1 Output) (RIN = RQ) 100 70 4.00 TA = 70°C 3.75 TA = 25°C 3.50 3.25 RIN = RQ 3.00 Q=5 2.75 2.50 2.25 2.00 1.75 1.50 Q = 2.5 1.25 1.00 0.75 Q=1 0.50 0.25 0 100 120 140 160 180 200 220 240 260 280 300 NOMINAL fO (kHz) 1562-2 G5 THD (AMPLITUDE BELOW FUNDAMENTAL) (dB) RIN = RQ 40 PEAK BP GAIN (dB) 45 2.75 PEAK BP GAIN (dB) TA = 70°C TA = 25°C 50 LP NOISE (µVRMS) Peak BP Gain vs Nominal fO (VS = ±2.5V) (Figure 3, V1 Output) Peak BP Gain vs Nominal fO (VS = ±5V) (Figure 3, V1 Output) Q Error vs Nominal fO (VS = ±2.5V) 1k 1562-2 G09 U U U PIN FUNCTIONS Power Supply Pins: The V + and V – pins should be bypassed with 0.1µF capacitors to an adequate analog ground or ground plane. These capacitors should be connected as closely as possible to the supply pins. Pins 4, 7, 14 and 17 are internally connected to V – (Pin 16) and should also be tied to the same point as Pin 16 for best shielding. Low noise linear supplies are recommended. Switching supplies are not recommended as they will lower the filter dynamic range. Analog Ground (AGND): The AGND pin is the midpoint of a resistive voltage divider, developing a potential halfway between the V + and V – pins, with an equivalent series resistance nominally 7k. This serves as an internal ground reference. Filter performance will reflect the quality of the analog signal ground and an analog ground plane surrounding the package is recommended. The analog ground plane should be connected to any digital ground at a single point. For dual supply operation, the AGND pin 15622fa 4 LTC1562-2 U U U PIN FUNCTIONS should be connected to the ground plane (Figure 1). For single supply operation, the AGND pin should be bypassed to the ground plane with at least a 0.1µF capacitor (at least 1µF for best AC performance) (Figure 2). ANALOG GROUND PLANE 1 20 2 19 3 18 4 17 V+ 5 16 0.1µF 6 15 7 14 8 13 9 12 10 11 LTC1562-2 SINGLE-POINT SYSTEM GROUND V– Shutdown (SHDN): When the SHDN input goes high or is open-circuited, the LTC1562-2 enters a “zero-power” shutdown state and only junction leakage currents flow. The AGND pin and the amplifier outputs (see Figure 3) assume a high impedance state and the amplifiers effectively disappear from the circuit. (If an input signal is applied to a complete filter circuit while the LTC1562-2 is in shutdown, some signal will normally flow to the output through passive components around the inactive op amps.) A small pull-up current source at the SHDN input defaults the LTC1562-2 to the shutdown state if the SHDN pin is left floating. Therefore, the user must connect the SHDN pin to a logic “low” (0V for ±5V supplies, V – for 5V total supply) for normal operation of the LTC1562-2. (This convention permits true “zero-power” shutdown since not even the driving logic must deliver current while the part is in shutdown.) With a single supply voltage, use V – for logic “low,” do not connect SHDN to the AGND pin. 0.1µF DIGITAL GROUND PLANE (IF ANY) 1562-2 F01 1/4 LTC1562-2 *R1 AND C ARE PRECISION INTERNAL COMPONENTS Figure 1. Dual Supply Ground Plane Connection (Including Substrate Pins 4, 7, 14, 17) 1 sR1C* C – ANALOG GROUND PLANE 1 20 2 19 3 18 4 17 V+ 5 0.1µF 6 15 7 14 8 13 9 12 10 11 SINGLE-POINT SYSTEM GROUND LTC1562-2 + V2 16 INV R2 V1 RQ ZIN 1µF + – V +/2 REFERENCE VIN IN EACH CASE, RESPONSE RESPONSE ZIN TYPE AT V1 AT V2 R BANDPASS LOWPASS C HIGHPASS BANDPASS DIGITAL GROUND PLANE (IF ANY) 1562-2 F01 fO = (200kHz) ( ( ) Q = RQ 200kHz R2 fO 7958Ω R2 ) 1562-2 F03 Figure 3. Equivalent Circuit of a Single 2nd Order Section (Inside Dashed Line) Shown in Typical Connection. Form of ZIN Determines Response Types at the Two Outputs (See Table) Figure 2. Single Supply Ground Plane Connection (Including Substrate Pins 4, 7, 14, 17) 15622fa 5 LTC1562-2 U U U PIN FUNCTIONS INV A, INV B, INV C, INV D: Each of the INV pins is a virtualground summing point for the corresponding 2nd order section. For each section, all three external components ZIN, R2, RQ connect to the INV pin as shown in Figure 3 and described further in the Applications Information. Note that the INV pins are sensitive internal nodes of the filter and will readily receive any unintended signals that are capacitively coupled into them. Capacitance to the INV nodes will also affect the frequency response of the filter sections. For these reasons, printed circuit connections to the INV pins must be kept as short as possible, less than one inch (2.5cm) total and surrounded by a ground plane. V1 A, V1 B, V1 C, V1 D: Output Pins. Provide a bandpass, highpass or other response depending on external circuitry (see Applications Information section). Each V1 pin also connects to the RQ resistor of the corresponding 2nd order filter section (see Figure 3 and Applications Information). Each output is designed to drive a nominal net load of 4kΩ and 30pF, which includes the loading due to the external RQ. Distortion performance improves when the outputs are loaded as lightly as possible. V2 A, V2 B, V2 C, V2 D: Output Pins. Provide a lowpass, bandpass or other response depending on external circuitry (see Applications Information section). Each V2 pin also connects to the R2 resistor of the corresponding 2nd order filter section (see Figure 3 and Applications Information). Each output is designed to drive a nominal net load of 4kΩ and 30pF, which includes the loading due to the external R2. Distortion performance improves when the outputs are loaded as lightly as possible. W BLOCK DIAGRA Overall Block Diagram Showing Four 3-Terminal 2nd Order Sections INV V1 V2 A V+ V1 V2 B – – C ∫ + V+ INV C ∫ + SHUTDOWN SWITCH V– R 2ND ORDER SECTIONS R SHUTDOWN SWITCH SHDN AGND D C + + ∫ V– – ∫ – C C 1562-2 BD INV V1 V2 INV V1 V2 15622fa 6 LTC1562-2 U W U U APPLICATIONS INFORMATION The LTC1562-2 contains four matched, 2nd order, 3-terminal universal continuous-time filter blocks, each with a virtual-ground input node (INV) and two rail-to-rail outputs (V1, V2). In the most basic application, one such block and three external resistors provide 2nd order lowpass and bandpass responses simultaneously (Figure 3, with a resistor for ZIN). The three external resistors program fO, Q and gain. A combination of internal precision components and external resistor R2 sets the center frequency fO of each 2nd order block. The LTC1562-2 is trimmed at manufacture so that fO will be 200kHz ±0.5% if the external resistor R2 is exactly 7958Ω. The LTC15622 is a higher frequency, pin compatible variant of the LTC1562, with different internal R and C values and higher speed amplifiers. However, lowpass/bandpass filtering is only one specific application for the 2nd order building blocks in the LTC1562-2. Highpass response results if the external impedance ZIN in Figure 3 becomes a capacitor CIN (whose value sets only gain, not critical frequencies) as described below. Responses with zeroes (e.g, elliptic or notch responses) are available by feedforward connections with multiple 2nd order blocks (see Typical Applicatons). Moreover, the virtual-ground input gives each 2nd order section the built-in capability for analog operations such as gain (preamplification), summing and weighting of multiple inputs, or accepting current or charge signals directly. These Operational FilterTM frequency-selective building blocks are nearly as versatile as op amps. The user who is not copying exactly one of the Typical Applications schematics shown later in this data sheet is urged to read carefully the next few sections through at least Signal Swings, for orientation about the LTC1562-2, before attempting to design custom application circuits. Also available free from LTC, and recommended for designing custom filters, is the general-purpose analog filter design software FilterCADTM for Windows®. This software includes tools for finding the necessary f0, Q and gain parameters to meet target filter specifications such as frequency response. Setting fO and Q Each of the four 2nd order sections in the LTC1562-2 can be programmed for a standard filter function (lowpass, bandpass or highpass) when configured as in Figure 3 with a resistor or capacitor for ZIN. These transfer functions all have the same denominator, a complex pole pair with center frequency ωO = 2πfO and quality parameter Q. (The numerators depend on the response type as described below.) External resistors R2 and RQ set fO and Q as follows: fO = Q =  7958Ω  1 = (200kHz) R2  2πC (R1)R2  RQ = (R1)R2 RQ (7958Ω)R2 = RQ  200kHz    R2  fO  R1 = 7958Ω and C = 100pF are internal to the LTC1562-2 while R2 and RQ are external. A typical design procedure proceeds from the desired fO and Q as follows, using finite-tolerance fixed resistors. First find the ideal R2 value for the desired fO: 2  200kHz  R2(Ideal) =   (7958Ω)  fO  Then select a practical R2 value from the available finitetolerance resistors. Use the actual R2 value to find the desired RQ, which also will be approximated with finite tolerance: RQ = Q (7958Ω)R2 The fO range is approximately 20kHz to 300kHz, limited mainly by the magnitudes of the external resistors required. As shown above, R2 varies with the inverse square of fO. This relationship desensitizes fO to R2’s tolerance (by a factor of 2 incrementally), but it also implies that R2 has a wider range than fO. (RQ and RIN also Operational Filter and FilterCAD are trademarks of Linear Technology Corporation. Windows is a registered trademark of Microsoft Corporation. 15622fa 7 LTC1562-2 U U W U APPLICATIONS INFORMATION tend to scale with R2.) At high fO these resistors fall below 4k, heavily loading the outputs of the LTC1562-2 and leading to increased THD and other effects. At the other extreme, a lower fO limit of 20kHz reflects an arbitrary upper resistor limit of 1MΩ. The LTC1562-2’s MOS input circuitry can accommodate higher resistor values than this, but junction leakage current from the input protection circuitry may cause DC errors. The 2nd order transfer functions HLP(s), HBP(s) and HHP(s) (below) are all inverting so that, for example, at DC the lowpass gain is – HL. If two such sections are cascaded, these phase inversions cancel. Thus, the filter in the application schematic on the first page of this data sheet is a dual DC preserving, noninverting, rail-to-rail lowpass filter, approximating two “straight wires with frequency selectivity.” Basic Lowpass When ZIN of Figure 3 is a resistor of value RIN, a standard 2nd order lowpass transfer function results from VIN to V2 (Figure 5): – HLω2O V2(s) = HLP (s) = 2 VIN(s) s + (ω O / Q)s + ω2O HL = R2/RIN is the DC gain magnitude. (Note that the transfer function includes a sign inversion.) Parameters RIN VIN RQ VOUT INV fL fO 1562 F05 Figure 5. Basic Lowpass Configuration HP HL 0.707 HL fH fO ; fO = fL fH fH – fL   2  1 –1 fL = fO  +   + 1    2Q  2Q      2  1 1 fH = fO  +   + 1   2Q  2Q    HP HH 0.707 HH fC fC fP f (LOG SCALE) Q= HIGHPASS RESPONSE GAIN (V/V) 0.707 HB V2 2nd ORDER LOWPASS RESPONSE GAIN (V/V) GAIN (V/V) BANDPASS RESPONSE V1 1/4 LTC1562-2 Figure 4 shows further details of 2nd order lowpass, bandpass and highpass responses. Configurations to obtain these responses appear in the next three sections. HB R2 2   1  1  fC = fO  1 –  +  1– 2  + 1  2Q2   2Q  fP = fO 1 – 1 1562-2 F04   2  1  1     fC = fO   1 – +  1–  + 1 2  2Q2    2Q     –1 –1 2Q2   1 HP = HL  1 1  1– Q 4Q2 fP f (LOG SCALE) f (LOG SCALE)        1  fP = fO  1 –  2Q2     1 HP = HH  1 1  1– Q 4Q2       Figure 4. Characteristics of Standard 2nd Order Filter Responses 15622fa 8 LTC1562-2 U U W U APPLICATIONS INFORMATION ωO (= 2πfO) and Q are set by R2 and RQ as above. For a 2nd order lowpass response the gain magnitude becomes QHL at frequency fO, and for Q > 0.707, a gain peak occurs at a frequency below fO, as shown in Figure 4. Basic Bandpass There are two different ways to obtain a bandpass function in Figure 3, both of which give the following transfer function form: HBP (s) = – HB (ω O / Q)s CIN VIN RQ INV CIN RIN VIN VIN R2 RQ RQ R2 VOUT V1 V2 VOUT INV V1 V2 2nd ORDER 2nd ORDER 1/4 LTC1562-2 1/4 LTC1562-2 1562-2 F06 (a) Resistive Input R2 VOUT s2 + (ω O / Q)s + ω O2 The value of the gain parameter HB depends on the circuit configuration as follows. When ZIN is a resistor of value RIN, a bandpass response results at the V1 output (Figure 6a) with a gain parameter HB = RQ/RIN. Alternatively, a capacitor of value CIN gives a bandpass response at the V2 output (Figure 6b), with the same HBP(s) expression, and the gain parameter now HB = (RQ/7958Ω)(CIN/100pF). This transfer function has a gain magnitude of HB (its peak value) when the frequency equals fO and has a phase shift of 180° at that frequency. Q measures the sharpness of the peak (the ratio of fO to – 3dB bandwidth) in a 2nd order bandpass function, as illustrated in Figure 4. ωO = 2πfO and Q are set by R2 and RQ as described previously in Setting fO and Q. INV HH = CIN/100pF is the highpass gain parameter. Parameters ωO = 2πfO and Q are set by R2 and RQ as above. For a 2nd order highpass response the gain magnitude at frequency fO is QHH, and approaches HH at high frequencies (f >> fO). For Q > 0.707, a gain peak occurs at a frequency above fO as shown in Figure 4. The transfer function includes a sign inversion. (b) Capacitive Input Figure 6. Basic Bandpass Configurations Basic Highpass When ZIN of Figure 3 is a capacitor of value CIN, a highpass response appears at the V1 output (Figure 7). V1(s) – HHs2 = HHP (s) = 2 VIN(s) s + (ω O / Q)s + ω 2O V1 V2 2nd ORDER 1/4 LTC1562-2 1562-2 F07 Figure 7. Basic Highpass Configuration Signal Swings The V1 and V2 outputs are capable of swinging to within roughly 100mV of each power supply rail. As with any analog filter, the signal swings in each 2nd order section must be scaled so that no output overloads (saturates), even if it is not used as a signal output. (Filter literature often calls this the “dynamics” issue.) When an unused output has a larger swing than the output of interest, the section’s gain or input amplitude must be scaled down to avoid overdriving the unused output. The LTC1562-2 can still be used with high performance in such situations as long as this constraint is followed. For an LTC1562-2 section as in Figure 3, the magnitudes of the two outputs V2 and V1, at a frequency ω = 2πf, have the ratio, | V2( jω ) | (200kHz) = | V1( jω ) | f regardless of the details of ZIN. Therefore, an input frequency above or below 200kHz produces larger output amplitude at V1 or V2, respectively. This relationship can guide the choice of filter design for maximum dynamic range in situations (such as bandpass responses) where there is more than one way to achieve the desired frequency response with an LTC1562-2 section. 15622fa 9 LTC1562-2 U W U U APPLICATIONS INFORMATION Because 2nd order sections with Q ≥ 1 have response peaks near fO, the gain ratio above implies some rules of thumb: fO < 200kHz ⇒ V2 tends to have the larger swing fO > 200kHz ⇒ V1 tends to have the larger swing. The following situations are convenient because the relative swing issue does not arise. The unused output’s swing is naturally the smaller of the two in these cases: Lowpass response (resistor input, V2 output, Figure 5) with fO < 200kHz Bandpass response (capacitor input, V2 output, Figure 6b) with fO < 200kHz Bandpass response (resistor input, V1 output, Figure 6a) with fO > 200kHz Highpass response (capacitor input, V1 output, Figure 7) with fO > 200kHz The LTC1562, a lower frequency variant of the LTC1562 -2, has a design center fO of 100kHz compared to 200kHz in the LTC1562-2. The rules summarized above apply to the LTC1562 but with 100kHz replacing the 200kHz limits. Thus, an LTC1562 highpass filter section with fO above 100kHz automatically satisfies the desirable condition of the unused output carrying the smaller signal swing. RIN 7.87k VIN RQ 5.49k INV R2 7.87k V1 V2 2nd ORDER 1/4 LTC1562-2 CL 30pF VOUT RL (EXTERNAL LOAD RESISTANCE) 1562-2 F08 Figure 8. 200kHz, Q = 0.7 Lowpass Circuit for Distortion vs Loading Test Low Level or Wide Range Input Signals The LTC1562-2 contains a built-in capability for low noise amplification of low level signals. The ZIN impedance in each 2nd order section controls the block’s gain. When set for unity passband gain, a 2nd order section can deliver an output signal 99dB above the noise level. If low level inputs require further dynamic range, reducing the value of ZIN boosts the signal gain while reducing the input referred noise. This feature can increase the SNR for low level signals. Varying or switching ZIN is also an efficient way to effect automatic gain control (AGC). From a system viewpoint, this technique boosts the ratio of maximum signal to minimum noise, for a typical 2nd order lowpass response (Q = 1, fO = 200kHz), to 114dB. Input Voltages Beyond the Power Supplies Properly used, the LTC1562-2 can accommodate input voltage excursions well beyond its supply voltage. This requires care in design but can be useful, for example, when large out-of-band interference is to be removed from a smaller desired signal. The flexibility for different input voltages arises because the INV inputs are at virtual ground potential, like the inverting input of an op amp with negative feedback. The LTC1562-2 fundamentally responds to input current and the external voltage VIN appears only across the external impedance ZIN in Figure 3. To accept beyond-the-supply input voltages, it is important to keep the LTC1562-2 powered on, not in shutdown mode, and to avoid saturating the V1 or V2 output of the 2nd order section that receives the input. If any of these conditions is violated, the INV input will depart from a virtual ground, leading to an overload condition whose recovery timing depends on circuit details. In the event that this overload drives the INV input beyond the supply voltages, the LTC1562-2 could be damaged. The most subtle part of preventing overload is to consider the possible input signals or spectra and take care that none of them can drive either V1 or V2 to the supply limits. Note that neither output can be allowed to saturate, even if it is not used as the signal output. If necessary the passband gain can be reduced (by increasing the impedance of ZIN in Figure 3) to reduce output swings. The final issue to be addressed with beyond-the-supply inputs is current and voltage limits. Current entering the virtual ground INV input flows eventually through the output circuitry that drives V1 and V2. The input current magnitude (VIN/ZIN in Figure 3) should be limited by design to less than 1mA for good distortion performance. On the other hand, the input voltage VIN appears across the 15622fa 10 LTC1562-2 U U W U APPLICATIONS INFORMATION external component ZIN, usually a resistor or capacitor. This component must of course be rated to sustain the magnitude of voltage imposed on it. Lowpass “T” Input Circuit The virtual ground INV input in the Operational Filter block provides a means for adding an “extra” lowpass pole to any resistor-input application (such as the basic lowpass, Figure 5, or bandpass, Figure 6a). The resistor that would otherwise form ZIN is split into two parts and a capacitor to ground added, forming an R-C-R “T” network (Figure 9). This adds an extra, independent real pole at a frequency: fP = 1 2πRPCT where CT is the new external capacitor and RP is the parallel combination of the two input resistors RINA and RINB. This pair of resistors must normally have a prescribed series total value RIN to set the filter’s gain as described above. The parallel value RP can however be set arbitrarily (to RIN/4 or less) which allows choosing a convenient standard capacitor value for CT and fine tuning the new pole with RP. RINA A practical limitation of this technique is that the CT capacitor values that tend to be required (hundreds or thousands of pF) can destabilize the op amp in Figure 3 if RINB is too small, leading to AC errors such as Q enhancement. For this reason, when RINA and RINB are unequal, preferably the larger of the two should be placed in the RINB position. Highpass “T” Input Circuit A method similar to the preceding technique adds an “extra” highpass pole to any capacitor-input application (such as the bandpass of Figure 6b or the highpass of Figure 7). This method splits the input capacitance CIN into two series parts CINA and CINB, with a resistor RT to ground between them (Figure 10). This adds an extra 1st order highpass corner with a zero at DC and a pole at the frequency: 1 2πRTCP where CP = CINA + CINB is the parallel combination of the two capacitors. At the same time, the total series capacitance CIN will control the filter’s gain parameter (HH in Basic Highpass). For a given series value CIN, the parallel value CP can still be set arbitrarily (to 4CIN or greater). fP = CINA RINB VIN CINB VIN CT RQ INV V1 R2 V2 RT RQ INV 2nd ORDER V1 R2 V2 2nd ORDER 1/4 LTC1562-2 1/4 LTC1562-2 1562-2 F09 1562-2 F10 Figure 9. Lowpass “T” Input Circuit Figure 10. Highpass “T” Input Circuit The procedure therefore is to begin with the target extra pole frequency fP. Determine the series value RIN from the gain requirement. Select a capacitor value CT such that RP = 1/(2πfPCT) is no greater than RIN/4, and then choose RINA and RINB that will simultaneously have the parallel value RP and the series value RIN. Such RINA and RINB can be found directly from the expression: The procedure then is to begin with the target corner (pole) frequency fP. Determine the series value CIN from the gain requirement (for example, CIN = HH(100pF) for a highpass). Select a resistor value RT such that CP = 1/(2πRTfP) is at least 4CIN, and select CINA and CINB that will simultaneously have the parallel value CP and the series value CIN. Such CINA and CINB can be found directly from the expression: 1 1 RIN ± RIN2 – (4RINRP) 2 2 1 1 CP ± CP2 – (4CINCP) 2 2 15622fa 11 LTC1562-2 This procedure can be iterated, adjusting the value of RT, to find convenient values for CINA and CINB since resistor values are generally available in finer increments than capacitor values. resistors and capacitors are provided to build applicationspecific filters. Also provided are terminals for inputs, outputs and power supplies. Notches and Elliptic Responses LTC1562/LTC1562-2 Demo Board The LTC demonstration board DC266 is assembled with an LTC1562 or LTC1562-2 in a 20-pin SSOP package and power supply decoupling capacitors. Jumpers on the board configure the filter chip for dual or single supply operation and power shutdown. Pads for surface mount Further circuit techniques appear in the LTC1562 data sheet under the heading “Notches and Elliptic Responses.” These techniques are directly applicable to the LTC1562-2 with the substitution of the different values for the internal components R1 and C. In the LTC1562-2, R1 is 7958Ω and C is 100pF. U TYPICAL APPLICATIONS 175kHz 8th Order Elliptic Highpass Filter CIN2 82pF RIN2 20.5k CIN3 47pF Amplitude Response CIN1 220pF 1 RQ1 9.09k R21 7.15k 2 3 5 5V 0.1µF R23 11.3k RQ3 59k 6 8 9 10 INV B INV C V1 B V1 C V2 B V2 C + V LTC1562-2 SHDN V2 A V 20 19 RQ2 26.7k 18 R22 10k V2 D V1 A V1 D INV A INV D 0 –10 –20 – 16 AGND 10 RIN3 45.3k – 5V* 0.1µF 15 13 R24 4.02k 12 RQ4 3.24k GAIN (dB) VIN –30 –40 –50 –60 –70 11 VOUT RIN4 40.2k –80 –90 50k CIN4 100pF 200k FREQUENCY (Hz) 900k 1562-2 TA03b *V – ALSO AT PINS 4, 7, 14 & 17 ALL RESISTORS 1% METAL FILM ALL CAPACITORS 5% STANDARD VALUES 1562-2 TA03a 15622fa 12 LTC1562-2 U TYPICAL APPLICATIONS Dual 5th Order 170kHz Elliptic Highpass Filter, Single 5V Supply CIN2 220pF RIN2 15k CI1 CIN1 100pF 82pF RQ1 43.2k RI1 2k R21 11.5k 2 3 5 5V 0.1µF 6 R23 11.5k CI3 CIN3 100pF 82pF RQ3 43.2k 8 9 10 VIN2 RI3 2k INV B INV C V1 B V1 C V2 B V2 C V+ LTC1562-2 V – SHDN AGND V2 A V2 D V1 A V1 D INV A INV D VOUT1 20 19 RQ2 7.68k 18 R22 6.34k 16 * 15 + 1 VIN1 1µF 13 R24 6.34k 12 RQ4 7.68k 11 VOUT2 RIN4 15k CIN4 220pF 1562-2 TA05a *GROUND ALSO AT PINS 4, 7, 14 & 17 Amplitude Response 10 0 – 10 GAIN (dB) – 20 – 30 – 40 – 50 – 60 – 70 – 80 – 90 10k 100k FREQUENCY (Hz) 1M 1562-2 TA05b 15622fa 13 LTC1562-2 U TYPICAL APPLICATIONS 100kHz 8th Order Bandpass Linear Phase, – 3dB BW = fCENTER/10 CIN1 10pF 1 VIN RQ1 78.7k R21 31.6k 2 3 5 5V 0.1µF 6 R23 35.7k RQ3 142k 8 9 10 INV B INV C V1 B V1 C V2 B V2 C V+ LTC1562-2 V – SHDN AGND V2 A V2 D V1 A V1 D INV A INV D CIN3 10pF 20 RIN2 178k 19 RQ2 76.8k 18 R22 30.1k 16 – 5V* 0.1µF 15 13 R24 28.7k 12 RQ4 118k 11 VOUT RIN4 221k 1562-2 TA6a *V – ALSO AT PINS 4, 7, 14 & 17 Frequency Response 10 AMPLITUDE RESPONSE –10 60 GROUP DELAY (µs) AMPLITUDE RESPONSE (dB) 0 – 20 –30 – 40 GROUP DELAY – 50 – 60 –70 60k 80k 100k 120k 0 140k FREQUENCY (Hz) 1562-2 TA06b 15622fa 14 LTC1562-2 U TYPICAL APPLICATIONS LTC1562-2 9th Order 200kHz Lowpass Elliptic Filter RIN2 7.32k CIN2 27pF Amplitude Response RIN1B 4.02k 1 VIN 180pF RQ1 6.04k R21 8.06k 2 3 5 5V 0.1µF 6 8 R23 12.4k RIN3 10.2k RQ3 5.36k 9 10 INVB INVC V1B V1C V2B V+ V2C V– LTC1562-2 SHDN AGND V2A V2D V1A V1D INVA INVD 20 10 RQ2 13k 19 0 –10 18 R22 6.04k –20 16 – 5V 0.1µF 15 13 12 GAIN (dB) RIN1A 4.02k –30 –40 –50 –60 R24 6.04k –70 –80 11 RQ4 14.3k –90 RIN4 6.04k CIN4 22pF –100 10 VOUT 100 FREQUENCY (kHz) 1000 1562-2 TA07b 1562-2 TA07a PINS 4, 7, 14, 17 (NOT SHOWN) ALSO CONNECT TO V – ALL RESISTORS ARE ±1%, ALL CAPACITORS ARE ±5% U PACKAGE DESCRIPTION G Package 20-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640) 5.20 – 5.38** (.205 – .212) 1.73 – 1.99 (.068 – .078) 7.07 – 7.33* (.278 – .289) 20 19 18 17 16 15 14 13 12 11 0° – 8° .13 – .22 (.005 – .009) .65 (.0256) BSC .55 – .95 (.022 – .037) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 7.65 – 7.90 (.301 – .311) .25 – .38 (.010 – .015) .05 – .21 (.002 – .008) 1 2 3 4 5 6 7 8 9 10 G20 SSOP 0501 3. DRAWING NOT TO SCALE *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDE **DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE 15622fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LTC1562-2 U TYPICAL APPLICATIO 256kHz Linear Phase 6th Order Lowpass Filter with a 2nd Order Allpass Phase Equalizer, Single Supply RFF1 6.19k VIN RB1 1.54k RIN1 7.5k R21 6.81k 2 3 5 5V 0.1µF 6 R23 4.12k RQ3 7.32k 8 9 10 INV B INV C V1 B V1 C V2 B V2 C V+ LTC1562-2 V– SHDN AGND V2 A V2 D V1 A V1 D INV A INV D 20 19 RQ2 4.12k 18 R22 6.19k 16 * 1µF 15 13 R24 4.12k 12 RQ4 7.32k + 1 RQ1 3.24k 11 VOUT RIN3 4.12k RIN4 4.12k CIN4 22pF 5% 1562-2 TA04a *GROUND ALSO AT PINS 4, 7, 14 & 17 ALL RESISTORS 1% METAL FILM Group Delay Response Amplitude Response 10 8 0 7 –10 6 DELAY (µs) GAIN (dB) –20 –30 –40 –50 5 4 3 –60 2 –70 1 –80 0 10k 100k FREQUENCY (Hz) 1M 50 100 150 200 250 300 FREQUENCY (kHz) 1562-2 TA04b 350 400 1562-2 TA04c RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1068-X Quad 2-Pole Switched Capacitor Building Block Clock Tuned LTC1560-1 5-Pole Elliptic Lowpass, fC = 1MHz/0.5MHz No External Components, SO8 LTC1562 Quad 2-Pole Active RC, 10kHz to 150kHz Same Pinout as LTC1562-2 LTC1563-2/LTC1563-3 4th Order Active RC Lowpass Filters fCUTOFF(MAX) = 256kHz, Resistor Programmable LTC1564 10kHz to 150kHz Digitally Controlled Filter and PGA Continuous Time Low Noise 8th Order with PGA LTC1565-31 650kHz Continuous Time, Linear Phase Lowpass Filter 7th Order, Differential Inputs and Outputs LTC1566-1 2.3MHz Continuous Time Lowpass Filter 7th Order, Differential Inputs and Outputs 15622fa 16 Linear Technology Corporation LT/TP 0102 1.5K REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com  LINEAR TECHNOLOGY CORPORATION 1998
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