DESCRIPTIO. LTC Low Power, 8th Order Progressive Elliptic, Lowpass Filter

Size: px

Start display at page:

Download "DESCRIPTIO. LTC Low Power, 8th Order Progressive Elliptic, Lowpass Filter"

Avis Baker
5 years ago
Views:

1 LTC9- Low Power, th Order Progressive Elliptic, Lowpass Filter FEATRES th Order Elliptic Filter in SO- Package Operates from Single.V to ±V Power Supplies db at.f CTOFF db at.f CTOFF db at f CTOFF Wide Dynamic Range µv RMS Wideband Noise.mA Supply Current with ±V Supplies.mA Supply Current with Single V Supply ma Supply Current with Single.V Supply APPLICATI O Telecommunication Filters Antialiasing Filters DESCRIPTIO S The LTC 9- is a monolithic th order lowpass filter featuring clock-tunable cutoff frequency and.ma power supply current with a single V supply. An additional feature of the LTC9- is operation with a single.v supply. The cutoff frequency (f CTOFF ) of the LTC9- is equal to the clock frequency divided by. The gain at f CTOFF is.db and the typical passband ripple is ±.db up to.9 f CTOFF. The stopband attenuation of the LTC9- features a progressive elliptic response reaching db attenuation at.f CTOFF, db attenuation at.f CTOFF and db attenuation at f CTOFF. With ±V supplies, the LTC9- cutoff frequency can be clock-tuned up to khz; with a single V supply, the maximum cutoff frequency is khz. The low power feature of the LTC9- does not penalize the device s dynamic range. With ±V supplies and an input range of.v RMS to.v RMS, the signal-to-(noise + THD) ratio is db. The wideband noise of the LTC9- is µv RMS. Other filter responses with lower power or higher speed can be obtained. Please contact LTC marketing for details. The LTC9- is available in -pin PDIP and -pin SO packages., LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATI O Frequency Response Single.V Supply khz Elliptic Lowpass Filter +.µf.v.µf AGND V + V OT V V OT LTC9- CLK f CLK khz 9- TA TA

2 LTC9- ABSOLTE AXI RATI GS W W W Total Supply Voltage (V + to V )... V Maximum Voltage at Any Pin... (V.V) V (V + +.V) Operating Temperature Range LTC9-C... C to C LTC9-I... C to C Storage Temperature Range... C to C Lead Temperature (Soldering, sec)... C PACKAGE/ORDER I FOR AGND V + NC N PACKAGE -LEAD PDIP TOP VIEW V OT V NC CLK S PACKAGE -LEAD PLASTIC SO T JMAX = C, θ JA = C/W (N) T JMAX = C, θ JA = C/W (S) W ATIO ORDER PART NMBER LTC9-CN LTC9-CS LTC9-IN LTC9-IS S PART NMBER 9 9I Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS f CTOFF is the filter s cutoff frequency and is equal to f CLK /. The f CLK signal level is TTL or CMOS (clock rise or fall time µs), V S =.V to ±V, R L = k, T A = C, unless otherwise noted. All AC gains are measured relative to the passband gain. PARAMETER CONDITIONS MIN TYP MAX NITS Passband Gain (f IN.f CTOFF ), f CLK = khz... db f TEST =.khz, = V RMS.. db V S =.V, f CLK = khz... db f TEST =.khz, =.V RMS.. db Gain at.f CTOFF, f CLK = khz... db f TEST =.khz, = V RMS.. db V S =.V, f CLK = khz... db f TEST = khz, =.V RMS.. db Gain at.f CTOFF, f CLK = khz... db f TEST =.khz, = V RMS.. db V S =.V, f CLK = khz... db f TEST =.khz, =.V RMS.. db Gain at.9f CTOFF, f CLK = khz... db f TEST =.khz, = VRMS.. db V S =.V, f CLK = khz... db f TEST =.khz, =.V RMS.. db Gain at.9f CTOFF, f CLK = khz... db f TEST =.khz, = V RMS.. db V S =.V, f CLK = khz... db f TEST =.9kHz, =.V RMS.. db Gain at f CTOFF, f CLK = khz... db f TEST =.khz, = V RMS.. db V S =.V, f CLK = khz... db f TEST =.khz, =.V RMS.. db Gain at.f CTOFF, f CLK = khz db f TEST =.khz, = V RMS db V S =.V, f CLK = khz db f TEST =.khz, =.V RMS db

3 ELECTRICAL CHARACTERISTICS LTC9- f CTOFF is the filter s cutoff frequency and is equal to f CLK /. The f CLK signal level is TTL or CMOS (clock rise or fall time µs), V S =.V to ±V, R L = k, T A = C, unless otherwise noted. All AC gains are measured relative to the passband gain. PARAMETER CONDITIONS MIN TYP MAX NITS Gain at.f CTOFF, f CLK = khz db f TEST =.khz, = V RMS 9 9 db V S =.V, f CLK = khz db f TEST = khz, =.V RMS 9 9 db Output DC Offset (Input at AGND), f CLK = khz mv V S =.V, f CLK = khz mv V S =.V, f CLK = khz mv Output Voltage Swing. ±.. V V S =.V. ±.. V V S =.V. ±.9. V Power Supply Current f CLK = khz.. ma V S =.V f CLK = khz.. ma V S =.V f CLK = khz.. ma Maximum Clock Frequency. MHz V S =.V. MHz V S =.V. MHz Input Frequency Range f CLK / MHz Input Resistance kω Operating Power Supply Voltage ±. ±. V The denotes specificatons which apply over the full operating temperature range. TYPICAL PERFORMANCE CHARACTERISTICS W Passband Gain vs Frequency f CLK = khz f C = khz = V RMS G GAIN (DB) Transition Band Gain vs Frequency f CLK = khz f C = khz = V RMS G Stopband Gain vs Frequency f CLK = khz f C = khz = V RMS G

LTC9- TYPICAL PERFORMANCE CHARACTERISTICS W.. Passband Gain vs Clock Frequency, V S = Single.V V S = SINGLE.V =.V RMS.. Passband Gain vs Clock Frequency, V S = Single V V S = SINGLE V =.V RMS.. Passband Gain vs Clock Frequency, = V RMS.

4 LTC9- TYPICAL PERFORMANCE CHARACTERISTICS W.. Passband Gain vs Clock Frequency, V S = Single.V V S = SINGLE.V =.V RMS.. Passband Gain vs Clock Frequency, V S = Single V V S = SINGLE V =.V RMS.. Passband Gain vs Clock Frequency, = V RMS..... f CLK = khz f C = khz f CLK = khz f C =.khz..... f CLK = khz f C =.khz f CLK = khz f C = khz f CLK = MHz f C = khz..... f CLK = khz f C = khz f CLK =.MHz f C = khz f CLK = MHz f C = khz G 9- G 9- G Gain vs Supply Voltage f CLK = khz =.V RMS V S =.V V S = V PHASE (DEG) 9 Phase and Group Delay vs Frequency PHASE GROP DELAY V S = SINGLE V f CLK = khz f C = khz GROP DELAY (ms) V/DIV Transient Response.ms/DIV f CLK = MHz f IN = Hz V P-P SQARE WAVE 9- G9 9- G 9- G THD + NOISE (db) Dynamic Range THD + Noise vs (V RMS ) f CLK = khz f IN = khz V S =.V V S = V V S = ±V THD + NOISE (db) THD + Noise vs Frequency f CLK = khz = mv RMS V S =.V V S = V THD + NOISE (db) THD + Noise vs Frequency f CLK = khz V S = V V S =.V =.V RMS INPT VOLTAGE (V RMS ) 9- G INPT 9- G 9 = V RMS = V RMS INPT 9- G

5 TYPICAL PERFORMANCE CHARACTERISTICS SPPLY CRRENT (ma) Supply Current vs Supply Voltage f CLK = Hz C C C TOTAL SPPLY VOLTAGE (±V) W SPPLY CRRENT (ma) Supply Current vs Clock Frequency V S = V V S =.V CLOCK FREQENCY (MHz) OTPT VOLTAGE SWING (V) LTC9- Output Voltage Swing vs Temperature V S = ±.V V S = ±.V V S = ±.V V S = ±.V AMBIENT TEMPERATRE ( C) 9- G 9- G 9- G PIN FNCTIONS AGND (Pin ): Analog Ground. The quality of the analog signal ground can affect the filter performance. For either single or dual supply operation, 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 Pin should be connected to the analog ground plane. For single supply operation Pin should be bypassed to the analog ground plane with a.µf or larger capacitor. An internal resistive divider biases Pin to / the total power supply. Pin should be buffered if used to bias other ICs. Figure shows the connections for single supply operation. V +, V (Pins, ): Power Supply Pins. The V + (Pin ) and the V (Pin ) should be bypassed with a.µf capacitor to an adequate analog ground. The filter s power supplies should be isolated from other digital or high voltage analog supplies. A low noise linear supply is recommended. sing switching power supplies will lower the signal-to-noise ratio of the filter. nlike previous monolithic filters, the power supplies can be applied at any order, that is, the positive supply can be applied before the negative supply and vice versa. Figure shows the connection for dual supply operation..µf V +.µf AGND V OT V + V LTC9- V OT AGND V OT V OT V + V + V V.µF LTC9-.µF CLK CLK ANALOG GROND PLANE ANALOG GROND PLANE STAR SYSTEM GROND DIGITAL GROND PLANE k CLOCK SORCE STAR SYSTEM GROND DIGITAL GROND PLANE k CLOCK SORCE 9- F Figure. Connections for Single Supply Operation 9- F Figure. Connections for Dual Supply Operation

6 LTC9- PIN FNCTIONS NC (Pins, ): No Connection. Pins and are not connected to any internal circuity; they should be preferably tied to ground. (Pin ): Filter Input Pin. The filter input pin is internally connected to the inverting input of an op amp through a k resistor. CLK (Pin ): Clock Input Pin. Any TTL or CMOS clock source with a square wave output and % duty cycle (±%) is an adequate clock source for the device. The power supply for the clock source should not necessarily be the filter s power supply. The analog ground of the filter should be connected to clock s ground at a single point only. Table shows the clock s low and high level threshold value for a dual or a single supply operation. A pulse generator can be used as a clock source provided the high level ON time is greater than.µs (). Sine waves less than khz are not recommended for clock signal because excessive slow clock rise or fall times generate internal clock jitter. The maximum clock rise or APPLICATIONS INFORMATION Temperature Behavior W The power supply current of the LTC9- has a positive temperature coefficient. The GBW product of its internal op amps is nearly constant and the speed of the device does not degrade at high temperatures. Figures a, b and c show the behavior of the maximum passband of the device for various supplies and temperatures. The filter, fall is µs. The clock signal should be routed from the right side of the IC package to avoid coupling into any input or output analog signal path. A k resistor between the clock source and the clock input pin () will slow down the rise and fall times of the clock to further reduce charge coupling, Figure. Table. Clock Source High and Low Thresholds POWER SPPLY HIGH LEVEL LOW LEVEL Dual Supply = ±V.V.V Single Supply = V.V.V Single Supply = V.V.V Single Supply =.V.V.V V OT (Pin ): Filter Output Pin. Pin is the output of the filter and it can source or sink ma. Driving coaxial cables or resistive loads less than k will degrade the total harmonic distortion of the filter. When evaluating the device s dynamic range, a buffer is required to isolate the filter s output from coax cables and instruments. especially at ±V supply, has a passband behavior which is nearly temperature independent. Clock Feedthrough The clock feedthrough is defined as the RMS value of the clock frequency and its harmonics that are present at the filter s output pin (). The clock feedthrough is tested with V S =.V f CLK = khz =.V RMS T A = C T A = C T A = C Fa V S = V f CLK = MHz =.V RMS T A = C T A = C T A = C 9- Fb. 9 Figure a Figure b Figure c f CLK =.MHz = V RMS T A = C T A = C T A = C 9- Fc

7 APPLICATIONS INFORMATION W the input pin () shorted to the AGND pin and depends on PC board layout and on the value of the power supplies. With proper layout techniques the values of the clock feedthrough are shown on Table. Table. Clock Feedthrough V S CLOCK FEEDTHROGH.V µv RMS V µv RMS ±V µv RMS Any parasitic switching transients during the rise and fall edges of the incoming clock are not part of the clock feedthrough specifications. Switching transients have frequency contents much higher than the applied clock; their amplitude strongly depends on scope probing techniques as well as grounding and power supply bypassing. The clock feedthrough can be reduced, if bothersome, by adding a single RC lowpass filter at the output pin () of the LTC9-. Wideband Noise The wideband noise of the filter is the total RMS value of the device s noise spectral density and determines the operating signal-to-noise ratio. Most of the wideband noise frequency contents lie within the filter passband. The wideband noise cannot be reduced by adding post filtering. The total wideband noise is nearly independent of the clock frequency and depends slightly on the power Table. Wideband Noise V S WIDEBAND NOISE.V µv RMS V µv RMS ±V µv RMS LTC9- supply voltage (see Table ). The clock feedthrough specifications are not part of the wideband noise. Aliasing Aliasing is an inherent phenomenon of sampled data systems and it occurs for input frequencies approaching the sampling frequency. The internal sampling frequency of the LTC9- is times its cutoff frequency. For instance, if a 9kHz, mv RMS signal is applied at the input of an LTC9- operating with a khz clock, a khz, µv RMS alias signal will appear at the filter output. Table shows details. Table. Aliasing (f CLK = khz) INPT FREQENCY OTPT LEVEL OTPT FREQENCY ( = V RMS ) (Relative to Input) (Aliased Frequency) (khz) (db) (khz) f CLK /f C = :, f CTOFF = khz 9 (or ) (or ).. 9 (or ).. 9. (or.).. 99 (or ) (or.).. TYPICAL APPLICATIONS Single V Operation with Power Shutdown Single.V Supply Operation with Output Buffer SHTDOWN ON V CMOS LOGIC.µF.µF AGND V + V OT V V OT LTC9- CLK f CLK khz V V 9- TA.µF.µF AGND V + V OT V LTC9- CLK f CLK khz.v.v V + / LT.µF V OT 9- TA 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.

8 LTC9- TYPICAL APPLICATIONS Dual Supply Operation f IN = khz AGND V OT V OT V V + V V.µF LTC9-.µF f CLK CLK V khz V f C = khz THD + NOISE (db). INPT VOLTAGE (V RMS ) 9- TA PACKAGE DESCRIPTION.. (..) Dimensions in inches (millimeters) unless otherswise noted. N Package -Lead PDIP (Narrow.) (LTC DWG # --).. (..). ±. (. ±.).* (.) MAX.9. (.9.) ( ). (.) TYP. (.) MIN. ±. (. ±.). (.) MIN. ±. (. ±.). (.) MIN. ±.* (. ±.) N 9 *THESE DIMENSIONS DO NOT INCLDE MOLD FLASH OR PROTRSIONS. MOLD FLASH OR PROTRSIONS SHALL NOT EXCEED. INCH (.mm).. (..).. (..) S Package -Lead Plastic Small Outline (Narrow.) (LTC DWG # --) TYP..9 (..).. (..).9.9* (..) RELATED PARTS PART NMBER DESCRIPTON COMMENTS LTC Very Low Noise, High Accuracy, Quad niversal Filter Building Block ser-configurable, SSOP Package LTC9- Single Supply, Very Low Power, Elliptic LPF : f CLK /f C Ratio, -Pin SO Package LTC- Low Power th Order Butterworth LPF : and : f CLK /f C Ratio LTC- Low Power th Order Elliptic LPF : and : f CLK /f C Ratio LTC- Low Power th Order Linear Phase LPF : and : f CLK /f C Ratio (..) *DIMENSION DOES NOT INCLDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED." (.mm) PER SIDE ** DIMENSION DOES NOT INCLDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED." (.mm) PER SIDE Linear Technology Corporation McCarthy Blvd., Milpitas, CA 9- () -9 FAX: () - TELEX: (.) BSC.. (.9.9)..** (..9) SO 9 LT/GP 9 K PRINTED IN SA LINEAR TECHNOLOGY CORPORATION 99

FEATURES TYPICAL APPLICATIO. LTC Low Power 8th Order Pin Selectable Butterworth or Bessel Lowpass Filter DESCRIPTIO APPLICATIO S

FEATURES TYPICAL APPLICATIO. LTC Low Power 8th Order Pin Selectable Butterworth or Bessel Lowpass Filter DESCRIPTIO APPLICATIO S FEATRES Pin Selectable Butterworth or Bessel Response ma Supply Current with ±V Supplies f CTOFF up to khz µv RMS Wideband Noise THD