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LTC1065 DC Accurate, Clock-Tunable Linear Phase 5th Order Bessel Lowpass Filter
FEATURES

DESCRIPTIO
Clock-Tunable Cutoff Frequency 1mV DC Offset (Typical) 80dB CMR (Typical) Internal or External Clock 50VRMS Clock Feedthrough 100:1 Clock-to-Cutoff Frequency Ratio 80VRMS Total Wideband Noise 0.004% Noise + THD at 2VRMS Output Level 50kHz Maximum Cutoff Frequency Cascadable for Faster Roll-Off Operates from 2.375 to 8V Power Supplies Self-Clocking with 1 RC Available in 8-Pin DIP and 16-Pin SW Packages
The LTC(R)1065 is the first monolithic filter providing both clock-tunability with low DC output offset and over 12-bit DC accuracy. The frequency response of the LTC1065 closely approximates a 5th order Bessel polynomial. With appropriate PCB layout techniques the output DC offset is typically 1mV and is constant over a wide range of clock frequencies. With 5V supplies and 4V input voltage range, the CMR of the device is typically 80dB. The filter cutoff frequency is controlled either by an internal or external clock. The clock-to-cutoff frequency ratio is 100 : 1. The on-board clock is nearly power supply independent and it is programmed via an external RC. The 50VRMS clock feedthrough of the device is considerably lower than other existing monolithic filters. The LTC1065 wideband noise is 80VRMS and it can process large AC input signals with low distortion. With 7.5V supplies, for instance, the filter handles up to 4VRMS (94dB S/N ratio) while the standard 1kHz THD is below 0.005%; 87dB dynamic range (S/N + THD) is obtained with input levels between 2VRMS and 2.5VRMS. The LTC1065 is available in 8-pin miniDIP and 16-pin SW packages. For a Butterworth response, see LTC1063 data sheet. The LTC1065 is pin compatible with the LTC1063.
APPLICATIO S

Audio Strain Gauge Amplifiers Anti-Aliasing Filters Low Level Filtering Digital Voltmeters Smoothing Filters Reconstruction Filters
, LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 4857860.
TYPICAL APPLICATIO
5V 4.99k VIN 1 2
3.4kHz Single 5V Supply Bessel Lowpass Filter
10 0 -10
8 7 LTC1065 6 5 VOUT 5V 0.1F
-20
+
GAIN (dB)
-30 -40 -50 -60 -70
1F TANT
4.53k
0.1F 3 4
13k*
* SELF-CLOCKING SCHEME
200pF*
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-80 -90 1 10 FREQUENCY (kHz) 100
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Frequency Response
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1
LTC1065
ABSOLUTE
(Note 1)
AXI U RATI GS
Operating Temperature Range (Note 7) LTC1065C .............................................. 0C to 70C LTC1065I ........................................... - 40C to 85C LTC1065M (OBSOLETE) .................. - 55C to 125C Lead Temperature (Soldering, 10 sec)................. 300C
Total Supply Voltage (V + to V -) .......................... 16.5V Power Dissipation ............................................. 400mW Voltage at Any Input .... (V - - 0.3V) VIN (V + + 0.3V) Burn-In Voltage ...................................................... 16V Storage Temperature Range ................ - 65C to 150C
PACKAGE/ORDER I FOR ATIO
TOP VIEW VIN 1 GND 2 V
-
8 VOS ADJ 7 VOUT 6V
+
ORDER PART NUMBER LTC1065CN8 LTC1065IN8
3
CLK OUT 4
5 CLK IN
N8 PACKAGE 8-LEAD PLASTIC DIP TJMAX = 100C, JA = 110C/W (N)
J8 PACKAGE 8-LEAD CERAMIC DIP TJMAX = 150C, JA = 100C/W (J)
LTC1065MJ8
OBSOLETE PACKAGE
Consider the N Package for an Alernate Source
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF, Lead Free Tape and Reel: Add #TRPBF, Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at VS = 5V, fCLK = 500kHz, fC = 5kHz, RL = 10k, TA = 25C unless otherwise specified.
PARAMETER Clock-to-Cutoff Frequency Ratio (fCLK / fC) Maximum Clock Frequency (Note 2) CONDITIONS 2.375V VS 7.5V VS = 7.5V VS = 5V VS = 2.5V 2.5V VS 7.5V, TA < 85C VS = 5V, fCLK = 25kHz, fC = 250Hz fIN = 250Hz fIN = 1kHz VS = 5V, fCLK = 500kHz, fC = 5kHz fIN = 100Hz fIN = 1kHz = 0.2fC fIN = 2.5kHz = 0.5fC fIN = 4kHz = 0.8fC fIN = 5kHz = fC fIN = 10kHz = 2fC fIN = 20kHz = 4fC MIN TYP 100 0.5 5 4 3 30 MAX UNITS MHz MHz MHz Hz 0.9fCLK - 3.1 - 41.0 0 - 0.175 - 0.972 - 2.13 - 3.1 - 14.15 - 41.15 - 2.7 - 39.0 dB dB dB dB dB dB dB dB dB
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ELECTRICAL CHARACTERISTICS
Minimum Clock Frequency (Note 3) Input Frequency Range Filter Gain
2
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W
WW
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W
TOP VIEW
NC 1 VIN 2 GND 3 NC 4 V-
5
16 VOS ADJ 15 NC 14 VOUT 13 NC 12
ORDER PART NUMBER LTC1065CSW LTC1065ISW
V+
NC 6 NC 7 CLK OUT 8
11 NC 10 NC 9
CLK IN
SW PACKAGE 16-LEAD PLASTIC SO WIDE TJMAX = 100C, JA = 85C/W
0

- 3.5 - 43.0

- 0.215 - 1.1 - 2.35 - 3.35 - 14.5 - 43.0
- 0.135 - 0.84 - 1.9 - 2.7 - 13.0 - 39.0
LTC1065
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at VS = 5V, fCLK = 500kHz, fC = 5kHz, RL = 10k, TA = 25C unless otherwise specified.
PARAMETER Filter Gain CONDITIONS VS = 2.375V, fCLK = 500kHz, fC = 5kHz fIN = 1kHz fIN = 2.5kHz fIN = 4kHz fIN = 5kHz fIN = 10kHz 2.375V VS 7.5V 2.375V VS 7.5V, 1Hz < f < fCLK VS = 7.5V, fC = 20kHz, fIN = 1kHz, 2VRMS VIN 2.5VRMS VS = 2.375V VS = 5V
ELECTRICAL CHARACTERISTICS
MIN

TYP - 0.185 - 1.0 - 2.15 - 3.1 -14.1 50 80 - 87 1.7/- 2.2 4.3/- 4.8 6.8/- 7.3 10 800 2 0 -4 10 20 25
MAX - 0.145 - 0.83 - 1.9 - 2.7 -13.0
UNITS dB dB dB dB dB VRMS VRMS dB V V V V V V nA M mV mV mV V/C V/C V/C kHz kHz kHz kHz kHz khz kHz kHz kHz V V V V V V mA mA mA mA mA mA mA mA mA
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- 0.225 - 1.1 - 2.35 - 3.35 - 14.5
Clock Feedthrough Wideband Noise (Note 4) THD + Wideband Noise (Note 5) Filter Output DC Swing
VS = 7.5V
1.5/- 2.0 1.3/- 1.8 4.0/- 4.5 3.8/- 4.3 6.5/- 7.0 6.3/- 6.8
Input Bias Current Dynamic Input Impedance Output DC Offset (Note 6)
Output DC Offset Drift
Self-Clocking Frequency (fOSC)
External CLK Pin Logic Thresholds
Power Supply Current
VS = 2.375V VS = 5V VS = 7.5V VS = 2.375V VS = 5V VS = 7.5V R (Pin 4 to 5) = 20k, C (Pin 5 to GND) = 470pF VS = 2.375V LTC1065C LTC1065M VS = 5V LTC1065C LTC1065M VS = 7.5V LTC1065C LTC1065M VS = 2.375V Min Logical "1" Max Logical "0" VS = 5V Min Logical "1" Max Logical "0" VS = 7.5V Min Logical "1" Max Logical "0" VS = 2.375V, fCLK = 500kHz LTC1065C LTC1065M VS = 5V, fCLK = 500kHz LTC1065C LTC1065M VS = 7.5V, fCLK = 500kHz LTC1065C LTC1065M
5

99 95 92 100 98 97 102 101 100
103 103 100 106 106 105 106 109 108 1.43 0.47 3 1 4.5 1.5 2.5
112 112 112 112 114 114 114 116 116

5.5

7.0

4.0 5.5 6.0 9 11 12 12.0 14.5 16.0
3
LTC1065
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The maximum clock frequency is arbitrarily defined as the frequency at which the filter AC response exhibits 1dB of gain peaking. Note 3: At limited temperature ranges (i.e., TA 50C) the minimum clock frequency can be as low as 10Hz. The typical minimum clock frequency is arbitrarily defined as the clock frequency at which the output DC offset changes by more than 1mV. Note 4: The wideband noise specification does not include the clock feedthrough. Note 5: To properly evaluate the filter's harmonic distortion an inverting output buffer is recommended. An output buffer (although recommended) is not necessarily needed when measuring output DC offset or wideband noise (see Figure 3). Note 6: The output DC offset is optimized for 5V supply. The output DC offset shifts when the power supplies change; however, this phenomenon is repeatable and predictable. Note 7: The LTC1065C is guaranteed to meet the specified performance from 0C to 70C and is designed, characterized and expected to meet specified performance from -40C to 85C but is not tested or QA sampled at these temperatures. The LTC1065I is guaranteed to meet specified performance from -40C to 85C.
TYPICAL PERFOR A CE CHARACTERISTICS
Self-Clocking Frequency vs R
110 100
LTC1065
90
4 R C = 200pF fOSC 1/RC
R PINS 4 TO 5 (k)
80 70 60 50 40 30 20 10 100 300 FREQUENCY (kHz) 500
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OUTPUT OFFSET (mV)
OUTPUT OFFSET (mV)
Gain vs Frequency; VS = 2.5V
10 0 -10 -20
GAIN (dB)
GAIN (dB)
-40 -50 -60 -70 -80 -90 1 VIN = 750mVRMS TA = 25C A. fCLK = 0.5MHz B. fCLK = 1MHz C. fCLK = 2MHz
A
B
C
-40 -50 -60 -70 -80 -90 VIN = 1.4VRMS TA = 25C 1 A. fCLK = 1MHz B. fCLK = 2MHz C. fCLK = 3MHz D. fCLK = 4MHz
A
BC
D
GAIN (dB)
-30
10 INPUT FREQUENCY (kHz)
4
UW
5 C
Output Offset vs Clock, Low Clock Rates
50 45 40 35 30 25 20 15 10 5 0 10 B A 110 EXTERNAL CLOCK FREQUENCY (Hz) 210 VS = 5V A. TA = 25C B. TA = 85C 5 4 3 2 1 0 -1 -2 -3 -4 -5
Output Offset vs Clock, Medium Clock Rates
VS = 7.5V
VS = 5V
VS = 2.5V
0
500 1000 EXTERNAL CLOCK FREQUENCY (kHz)
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Gain vs Frequency; VS = 5V
10 0 -10 -20 -30 10 0
Gain vs Frequency; VS = 7.5V
D -10 -20 -30 -40 -50 -60 -70 -80 -90 100 200
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A
BC
E
A. fCLK = 1MHz B. fCLK = 2MHz C. fCLK = 3MHz D. fCLK = 4MHz E. fCLK = 5MHz VIN = 1.4VRMS TA = 25C 1 10 INPUT FREQUENCY (kHz) 100 200
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100 200
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10 INPUT FREQUENCY (kHz)
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LTC1065
TYPICAL PERFOR A CE CHARACTERISTICS
THD + Noise vs Input Voltage; VS = Single 5V, AGND = 2V
1 fIN = 1kHz, TA = 25C
1 VIN = 0.75VRMS, S/N = 80dB fC = 5kHz, fCLK = 500kHz TA = 25C 0.1 THD + NOISE (%)
THD + NOISE (%)
0.1
THD (%)
B 0.01 A
A. fC = 5kHz, fCLK = 0.5MHz B. fC = 10kHz, fCLK = 1MHz 0.001 0.1
0.001
1 INPUT (VRMS)
THD vs Frequency; VS = 5V
1 VIN = 1.5VRMS fC = 10kHz, fCLK = 1MHz TA = 25C 0.1 THD + NOISE (%)
THD (%)
0.01
0.01
B A A. fC = 10kHz, fCLK = 1MHz B. fC = 20kHz, fCLK = 2MHz
THD (%)
0.001 1 5 FREQUENCY (kHz) 10
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Passband Gain and Phase vs Input Frequency
1 0 2.5V VS 7.5V, TA = 25C 40 0 -40
POWER SUPPLY CURRENT (mA)
-1 -2 -3 -4 -5 -6 100 fC =1kHz fCLK =100kHz fC =10kHz fCLK =1MHz A PHASE A B PHASE B
PHASE MISMATCH (DEG)
PASSBAND GAIN (dB)
1k 10k INPUT FREQUENCY (Hz)
UW
5
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THD vs Frequency; VS = Single 5V, AGND = 2V
1
THD + Noise vs Input Voltage; VS = 5V
fIN = 1kHz, TA = 25C
0.1 B
0.01
0.01
A A. fC = 10kHz, fCLK = 1MHz B. fC = 20kHz, fCLK = 2MHz
1
2 3 FREQUENCY (kHz)
4
5
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0.001 0.1
1 INPUT (VRMS)
5
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THD + Noise vs Input Voltage; VS = 7.5V
1 fIN = 1kHz TA = 25C
1
THD vs Frequency; VS = 7.5V
VIN = 2.5VRMS, S/N = 90dB fC = 10kHz, fCLK = 1MHz TA = 25C 0.1
0.1
0.01
0.001 0.1
1 INPUT (VRMS)
5
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0.001 1 5 FREQUENCY (kHz) 10
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Typical Phase Matching Device to Device
0.6 0.5 0.4 0.3 0.2 0.1 0 VS = 7.5V VIN = 1VRMS fC = 20kHz fCLK = 2MHz
15
Power Supply Current vs Power Supply Voltage
-40C 12 25C 9 85C 6
PHASE (DEG)
-80 -120 -160 -200 -240 100k
3
02
4
6 8 10 12 14 16 18 20 22 24 INPUT FREQUENCY (kHz)
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0 0 2 4 6 8 10 12 14 16 18 20 TOTAL POWER SUPPLY VOLTAGE (V)
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LTC1065
TYPICAL PERFOR A CE CHARACTERISTICS
Transient Response
45 40 35
GROUP DELAY (s)
HORIZONTAL: 0.1ms/DIV, VERTICAL: 2V/DIV VS = 5V, fC = 10kHz, VIN = 1kHz 3VP SQUARE WAVE
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PI FU CTIO S
Power Supply Pins (Pins 6, 3, N Package) The positive and negative supply pin should be bypassed with a high quality 0.1F ceramic capacitor. In applications where the clock pin (5) is externally swept to provide several cutoff frequencies, the output DC offset variation is minimized by connecting an additional 1F solid tantalum capacitor in parallel with the 0.1F disc ceramic. This technique was used to generate the graphs of the output DC offset variation versus clock; they are illustrated in the Typical Performance Characteristics section. When the power supply voltage exceeds 7V, and when V - is applied before V + (if V+ is allowed to go below ground) connect a signal diode between the positive supply pin and ground to prevent latch-up (see Typical Applications). Ground Pin (Pin 2, N Package) The ground pin merges the internal analog and digital ground paths. The potential of the ground pin is the reference for the internal switched-capacitor resistors, and the reference for the external clock. The positive input of the internal op amp is also tied to the ground pin. For dual supply operation, the ground pin should be connected to a high quality AC and DC ground. A ground plane, if possible, should be used. A poor ground will degrade DC offset and it will increase clock feedthrough, noise and distortion. A small amount of AC current flows out of the ground pin whether or not the internal oscillator is used. The frequency of the ground current equals the frequency of the clock. The average value of this current is approximately 55A, 110A, 170A for 2.5V, 5V and 7.5V supplies respectively. For single supply operation, the ground pin should be preferably biased at half supply (see Typical Applications). VOS Adjust Pin (Pin 8, N Package) The VOS adjust pin can be used to trim any small amount of output DC offset voltage or to introduce a desired output DC level. The DC gain from the VOS adjust pin to the filter output pin equals two. Any DC voltage applied to this pin will reflect at the output pin of the filter multiplied by two. If the VOS adjust pin is not used, it should be shorted to the ground pin. The DC bias current flowing into the VOS adjust pin is typically 10pA. The VOS adjust pin should always be connected to an AC ground; AC signals applied to this pin will degrade the filter response.
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Group Delay
30 25 20 15 10 5 0 0 3 12 6 9 15 INPUT FREQUENCY (kHz) 18 21 VS = 5V fC = 10kHz
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LTC1065 PI FU CTIO S
Input Pin (Pin 1, N Package) Pin 1 is the filter input and it is connected to an internal switched-capacitor resistor. If the input pin is left floating, the filter output will saturate. The DC input impedance of pin 1 is very high; with 5V supplies and 1MHz clock, the DC input impedance is typically 1G. A resistor RIN in series with the input pin will not alter the value of the filter's DC output offset (Figure 1). RIN should however, be limited to a maximum value (Table 1), otherwise the filter's passband will be affected. Refer to the Applications Information section for more details.
VIN RIN 1 2 V
-3
Table 1. RIN(MAX) vs Clock and Power Supply
RIN(MAX) VS = 7.5V fCLK = 4MHz fCLK = 3MHz fCLK = 2MHz fCLK = 1MHz fCLK = 500kHz fCLK = 100kHz 1.82k 3.01k 4.32k 9.09k 17.8k 95.3k VS = 5V - 2.49k 3.65k 8.25k 16.9k 90.9k VS = 2.5V - - 2.37k 7.5k 16.9k 90.9k
MAXIMUM LOAD CAPACITANCE (pF )
Output Pin (Pin 7, N Package) Pin 7 is the filter output. This pin can typically source over 20mA and sink 2mA. Pin 7 should not drive long coax cables, otherwise the filter's total harmonic distortion will degrade. The maximum load the filter output can drive and still maintain the distortion levels, shown in the Typical Performance Characteristics, is 20k. Clock Input Pin (Pin 5, N Package) An external clock, when applied to pin 5, tunes the filter cutoff frequency. The clock-to-cutoff frequency ratio is
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100:1. The high (VHIGH) and low (VLOW) clock logic threshold levels are illustrated in Table 2. Square wave clocks with duty cycles between 30% and 50% are strongly recommended. Sinewave clocks are not recommended.
Table 2. Clock Pin Threshold Levels
POWER SUPPLY VS = 2.5V VS = 5V VS = 7.5V VS = 8V VS = 5V, 0V VS = 12V, 0V VS =15V, 0V VHIGH 1.5V 3V 4.5V 4.8V 4V 9.6V 12V VLOW 0.5V 1V 1.5V 1.6V 3V 7.2V 9V
8 7 LTC1065 6 VOUT V+
Clock Output Pin (Pin 4, N Package) Any external clock applied to the clock input pin appears at the clock output pin. The duty cycle of the clock output equals the duty cycle of the external clock applied to the clock input pin. The clock output pin swings to the power supply rails. When the LTC1065 is used in a self-clocking mode, the clock of the internal oscillator appears at the clock output pin with a 30% duty cycle. The clock output pin can be used to drive other LTC1065s or other ICs. The maximum capacitance, CL(MAX), the clock output pin can drive is illustrated in Figure 2.
200 180 160 140 120 100 80 60 40 20 0 1 3 2 4 5 6 7 8 9 10 CLOCK FREQUENCY (MHz)
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5f CLK
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Figure 1.
VS = 2.5V
TA = 25C
VS = 5V VS = 7.5V
Figure 2. Maximum Load Capacitance at the Clock Output Pin
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7
LTC1065
TEST CIRCUIT
+
LT1022 VIN 1 2 3 V- 4 0.1F CLOCK IN
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VOUT
8 7 LTC1065 6 5 50k V+ 0.1F
-
50k
20pF
Figure 3. Test Circuit for THD
APPLICATI
S I FOR ATIO
Self-Clocking Operation The LTC1065 features an internal oscillator which can be tuned via an external RC. The LTC1065's internal oscillator is primarily intended for generation of clock frequencies below 500kHz. The first curve of the Typical Performance Characteristics section shows how to quickly choose the value of the RC for a given frequency. More precisely, the frequency of the internal oscillator is equal to: fCLK = K/RC For clock frequencies (fCLK) below 100kHz, K equals 1.07. Figure 4b shows the variation of the parameter K versus clock frequency and power supply. First choose the desired clock frequency (fCLK < 500kHz), then through Figure 4b pick the right value of K, set C = 200pF and solve for R. Example 1: fCUTOFF = 2kHz, fCLK = 200kHz, VS = 5V, TA = 25C, K = 1.0, C = 200pF then, R = (1.0)/(200kHz x 204pF) = 24.5k.
K
VIN
1 2
8 7
LTC1065
VOUT
V+
V-
3 4
6 5
R
C
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Figure 4a.
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Note a 4pF parasitic capacitance is assumed in parallel with the external 200pF timing capacitor. Figure 5 shows the clock frequency variation from - 40C to 85C. The 200kHz clock of Example 1 will change by -1.75% at 85C. For a limited temperature range, the internal oscillator of the LTC1065 can be used to generate clock frequencies above 500kHz (Figures 6 and 7). The data of Figure 6 is derived from several devices. For a given external (RC) value, the observed device-to-device clock frequency variation was 1% (VS = 5V), and 1.25% for VS = 2.5V. Example 2: fCUTOFF = 20kHz, fCLK = 2MHz, VS = 7.5V, TA = 25C, C = 10pF from Figure 6, K = 0.575, and, R = (0.575)/(2MHz x 14pF) = 20.5k.
1.25 1.20 1.15 1.10 1.05 1.00 0.95 0.90 0.85 0.80 0.75 100 300 400 500 200 INTERNAL CLOCK FREQUENCY (kHz)
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fCLK = K/RC C = 200pF TA = 25C
VS = 7.5V
VS = 5V
VS = 2.5V
Figure 4b. fCLK vs K
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LTC1065
APPLICATI
4 3
fCLK CHANGE NORMALIZED TO ITS 25C VALUE (%)
S I FOR ATIO
TA = -40C VS = 5V VS = 7.5V TA = 85C VS = 7.5V
C = 200pF VS = 2.5V
2 1 0 -1 -2 -3 -4 0
VS = 2.5V
VS = 5V
100 300 400 200 CLOCK FREQUENCY (kHz)
500
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Figure 5. fCLK vs Temperature
0.80 0.75 0.70 0.65 0.60 0.55 0.50 0.45 0.40 0.5 1.0 2.0 2.5 1.5 CLOCK FREQUENCY (MHz) 3.0
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fCLK = K/RC C = 10pF TA = 25C
K
VS = 7.5V VS = 5V
VS = 2.5V
Figure 6. fCLK vs K
0.80 0.75 0.70 0.65 0.60 0.55 0.50 0.45 0.40 0.5 VS = 2.5V 1.0 2.0 2.5 1.5 CLOCK FREQUENCY (MHz) 3.0
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fCLK = K/RC C = 10pF TA = 70C
K
VS = 7.5V VS = 5V
Figure 7. fCLK vs K
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A 4pF parasitic capacitance is assumed in parallel with the external 10pF capacitor. A 1% clock frequency variation from device to device can be expected. The 2MHz clock frequency designed above will typically drift to 1.74MHz at 70C (Figure 7). The internal clock of the LTC1065 can be overridden by an external clock provided that the external clock source can drive the timing capacitor C, which is connected from the clock input pin to ground. Output Offset The DC output offset of the LTC1065 is trimmed to typically less than 1mV. The trimming is done at VS = 5V. To obtain optimum DC offset performance, appropriate PC layout techniques should be used and the filter IC should be soldered to the PC board. A socket will degrade the output DC offset by typically 1mV. The output DC offset is sensitive to the coupling of the clock output pin 4 (N package) to the negative power supply pin 3 (N package). The negative supply pin should be well decoupled. When the surface mount package is used, all NC pins should be grounded. When the output DC voltage is measured with a voltmeter, the filter output pin should be buffered. Long test leads should be avoided. With fixed power supplies, the output DC offset should not change by more than 100V over 10Hz to 1MHz clock frequency variation. When the filter clock frequency is fixed, the output DC offset will typically change by - 4mV (2mV) when the power supply varies from 5V to 7.5V (2.5V). See Typical Performance Characteristics. Common Mode Rejection The common mode rejection is defined as the change of the output DC offset with respect to the DC change of the input voltage applied to the filter. CMR = 20log (VOS OUT /VIN)(dB) Table 3 illustrates the common mode rejection for three power supplies and three temperatures. The common mode rejection improves if the output offset is adjusted to approximately 0V. The output offset can be adjusted via pin 8 (N package). See Typical Applications.
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LTC1065
APPLICATI
POWER SUPPLY 2.5V 5V 7.5V
S I FOR ATIO
- 40C 84dB 82dB 80dB 25C 83dB 78dB 77dB 85C 80dB 77dB 76dB
Table 3. CMR Data, fCLK = 100kHz
VIN 1.8V 4V 6V 25C (VOS Nulled) 83dB 78dB 80dB
5mV/DIV
The above data is valid for clock frequencies up to 800kHz, 900kHz, 1MHz, for VS = 2.5V, 5V, 7.5V respectively.
Clock Feedthrough Clock feedthrough is defined as the RMS value of the clock frequency and its harmonics which are present at the filter's output pin. The clock feedthrough is tested with the filter input grounded and it depends on the quality of the PC board layout and power supply decoupling. Any parasitic switching transients during the rise and fall of the incoming clock, are not part of the clock feedthrough specifications; their amplitude strongly depends on scope probing techniques as well as ground quality and power supply bypassing. For a power supply VS = 5V, the clock feedthrough of the LTC1065 is 50VRMS; for VS = 7.5V, the clock feedthrough approaches 75VRMS. Figures 8 and 9 show a typical scope photo of the LTC1065 output pin when the input pin is grounded. The filter cutoff frequency was 1kHz, while scope bandwidth was chosen to be 1MHz so that switching transients above the 100kHz clock frequency would show. Wideband Noise The wideband noise data is used to determine the operating signal-to-noise ratio at a given distortion level. The wideband noise (VRMS) is nearly independent of the value of the clock frequency and excludes the clock feedthrough. The LTC1065's typical wideband noise is 80VRMS. Figure 9 shows the same scope photo as Figure 8 but with a more sensitive vertical scale. The clock feedthrough is imbedded in the filter's wideband noise. The peak-to-peak wideband noise of the filter can be clearly seen; it is approximately 420VP-P. Note that 420VP-P equals the 80VRMS wideband noise of the part multiplied by a crest factor of 5.25.
2s/DIV fCLK = 100kHz, fC = 1kHz, VS = 5V, 1MHz SCOPE BW
1065F08
0.5mV/DIV
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Figure 8. LTC1065 Output Clock Feedthrough + Noise
2s/DIV fCLK = 100kHz, fC = 1kHz, VS = 5V, 1MHz SCOPE BW
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Figure 9. LTC1065 Output Clock Feedthrough + Noise
Aliasing Aliasing is an inherent phenomenon of sampled data filters. It primarily occurs when the frequency of an input signal approaches the sampling frequency. For the LTC1065, an input signal whose frequency is in the range of fCLK 6% will generate an alias signal into the filter's passband and stopband. Table 4 shows details. Example: LTC1065, fCLK = 20kHz, fC = 200kHz, fIN = (19.6kHz, 100mVRMS) fALIAS = (400Hz, 3.16mVRMS)
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LTC1065
APPLICATI S I FOR ATIO
Table 4. Aliasing Data
OUTPUT AMPLITUDE REFERENCED TO INPUT SIGNAL - 0.01 - 0.98 - 3.13 - 4.79 - 7.21 - 10.43 - 14.14 - 21.84 - 28.98 - 35.31 - 40.94 - 45.96 - 50.46 - 58.29 - 64.90 - 80.20 dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB
INPUT FREQUENCY 0.9995 fCLK 0.995 fCLK 0.99 fCLK 0.9875 fCLK 0.985 fCLK 0.9825 fCLK 0.98 fCLK 0.975 fCLK 0.97 fCLK 0.965 fCLK 0.96 fCLK 0.955 fCLK 0.95 fCLK 0.94 fCLK 0.93 fCLK 0.9 fCLK
OUTPUT FREQUENCY 0.0005 fCLK 0.005 fCLK 0.01 fCLK 0.0125 fCLK 0.015 fCLK 0.0175 fCLK 0.02 fCLK 0.025 fCLK 0.03 fCLK 0.035 fCLK 0.04 fCLK 0.045 fCLK 0.05 fCLK 0.06 fCLK 0.07 fCLK 0.1 fCLK
U
An input RC can be used to attenuate incoming signals close to the filter clock frequency (Figure 10). A Bessel passband response will be maintained if the value of the input resistor follows Table 1.
R
W
U
UO
VIN C V-
0.1F
1 2 3 4
LTC1065
8 7 6 5
fCLK
VOUT V+
0.1F
fCLK 1 f CLK 20 2RC 10
1065 F10
Figure 10. Adding an Input Anti-Aliasing RC
1065fb
11
LTC1065
TYPICAL APPLICATIO S
Cascading Two LTC1065s for Steeper Roll-Off
VIN 1 2 -5V 0.1F 3 4 LTC1065 8 7 6 5 5V 0.1F
R
1 2 -5V 0.1F 3 4 LTC1065
8 7 6 5 VOUT 5V 0.1F
fC (1/RC)(1/100) WIDEBAND NOISE = 110VRMS ATTENUATION AT f = 2fC = 60dB
12
U
Sharing Clock for Multichannel Applications
VIN 1 2 -5V 0.1F 3 4 LTC1065 8 7 6 5 VOUT 5V 0.1F
C
R
C
VIN
1 2
8 7 LTC1065 6 5 VOUT 5V 0.1F
1065 TA03
-5V 0.1F
3 4
1065 TA02
1065fb
LTC1065
PACKAGE DESCRIPTIO
CORNER LEADS OPTION (4 PLCS)
.045 - .068 (1.143 - 1.650) FULL LEAD OPTION .300 BSC (7.62 BSC)
.008 - .018 (0.203 - 0.457)
NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE OR TIN PLATE LEADS
U
J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic)
(Reference LTC DWG # 05-08-1110)
.405 (10.287) MAX 8 7 6 5 .005 (0.127) MIN .023 - .045 (0.584 - 1.143) HALF LEAD OPTION .025 (0.635) RAD TYP 1 2 3 .220 - .310 (5.588 - 7.874) 4 .200 (5.080) MAX .015 - .060 (0.381 - 1.524) 0 - 15 .045 - .065 (1.143 - 1.651) .014 - .026 (0.360 - 0.660) .100 (2.54) BSC .125 3.175 MIN
J8 0801
OBSOLETE PACKAGE
1065fb
13
LTC1065
PACKAGE DESCRIPTIO U
N Package 8-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510)
.400* (10.160) MAX 8 7 6 5 .255 .015* (6.477 0.381) 1 .300 - .325 (7.620 - 8.255) 2 3 4 .130 .005 (3.302 0.127) .045 - .065 (1.143 - 1.651) .065 (1.651) TYP .120 (3.048) .020 MIN (0.508) MIN .018 .003 (0.457 0.076)
N8 1002
.008 - .015 (0.203 - 0.381)
(
+.035 .325 -.015 8.255 +0.889 -0.381
)
.100 (2.54) BSC
INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
NOTE: 1. DIMENSIONS ARE
1065fb
14
LTC1065
PACKAGE DESCRIPTIO
.030 .005 TYP N
.420 MIN
1
2
3
RECOMMENDED SOLDER PAD LAYOUT 1 .291 - .299 (7.391 - 7.595) NOTE 4 .010 - .029 x 45 (0.254 - 0.737)
0 - 8 TYP
.005 (0.127) RAD MIN
.009 - .013 (0.229 - 0.330)
NOTE 3 .016 - .050 (0.406 - 1.270)
NOTE: 1. DIMENSIONS IN
INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS 4. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
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.
U
SW Package 16-Lead Plastic Small Outline (Wide .300 Inch)
(Reference LTC DWG # 05-08-1620)
.050 BSC .045 .005 .398 - .413 (10.109 - 10.490) NOTE 4 16 15 14 13 12 11 10 9 N .325 .005 NOTE 3 .394 - .419 (10.007 - 10.643) N/2 N/2 2 3 4 5 6 7 8 .093 - .104 (2.362 - 2.642) .037 - .045 (0.940 - 1.143) .050 (1.270) BSC .004 - .012 (0.102 - 0.305) .014 - .019 (0.356 - 0.482) TYP
S16 (WIDE) 0502
1065fb
15
LTC1065
TYPICAL APPLICATIO S
Single 5V Supply Operation (fC = 3.4kHz)
5V 4.99k VIN 1 2 8 7 LTC1065 6 5 VOUT 5V 0.1F VIN 1 2 13k 200pF
1065 TA04
+
1F TANT
4.53k
0.1F
3 4
RELATED PARTS
PART NUMBER LTC1063 LTC1064-1/2/3/4/7 LTC1164-5/6/7 LTC1264-7 LTC1569-6/7 DESCRIPTION Clock Tunable, 5th Order Bessel Low Pass Clock Tunable, 8th Order Low Pass Clock Tunable, Low Power, 8th Order Low Pass Clock Tunable, 8th Order Low Pass Clock Tunable, 10th Order Low Pass COMMENTS Internal or External Clock, 1mVDC Offset, Cascadable Elliptic, Butterworth, Bessel, Cauer or Linear Phase Butterworth, Bessel or Elliptic, FO Max = 20KHz Flat Group Delay, FO Max = 200KHz, Steeper Roll-Off than Bessel Internal or External Clock, Root Raised Cosine Response
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
U
Adjusting VOS(OUT) for 7.5 Supply Operation
7.5V 10k 10k LT1009 8 7 LTC1065 6 5 fCLK 0.1F * OPTIONAL, 1N4148
1065 TA05
2.5mV VOUT V+ 7.5V *
V- -7.5V 1F TANT
3
+
0.1F
4
1065fb LT/LT 0705 REV B * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 1993

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