EDNE December 2012 - (Page 38)

designideas 0.02 F FILM 1.62k 1.62k + 0.02 F FILM VDC ADJUST 1 F FILM DC BLOCK OP AMP AND ADC UNDER TEST 3.3V 10k + 15V OUTPUT AMPLITUDE ADJUST 2k TRIMPOT –15V 1.24k CHRISTMAS LAMP C7 120V 5W LT1468-2 − 3.3V 324 1% 470 pF NPO 6.65k 1% 22 pF VREF CS LTC2361 SDO SCK GND 0VDD VDD 1k LTC6255 − AIN 100 10k 1% HP 3325 ADC CLOCK GENERATOR Figure 2 The Wien-bridge oscillator drives the op amp and ADC pair under test. The resulting FFT is clean after windowing, but not exceptional, as Figure 3 shows. Figure 3 This 4096-point FFT was achieved using an unlocked oscillator with a 92-dB Blackman-Harris window. Note that the peak does not look like –1 dBFS and that there is power in the bins around the peak. OSCILLATOR INCOHERENT, CLEANED UP WITH 92-dB BLACKMAN HARRIS WINDOW 0 DOESN’T LOOK LIKE −1 dBFS –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 0 512 EDN DI5291 Fig 2.eps DIANE POWER IN BINS OUTSIDE THE PEAK VIN=–1 dBFS, 5 kHz FS=125 kSPS SFDR=89 dB NOT AN ACCURATE PICTURE OF THE HARMONICS 1024 1536 2048 environment? At 5 kHz, a passive filter with notches would be large and fussy. I thought of detuning the Wien-bridge oscillator by reducing the gain, thereby converting it into a filter. But then it occurred to me that a gentle, analog sinusoidal nudge from a distorting but well-locked external oscillator might be enough to tweak the Wien-bridge frequency to where it needed to be. I decided to try injecting a sinusoid into the input of the Wien-bridge op-amp circuit, and opted to use a high series impedance to avoid simultaneously injecting noise and distortion. I came up with 200k—about 1000× the impedances already there—and put it in as shown on EDN DI5291 Fig 3.eps the left side of Figure 4 (the “new input”). I set up the Agilent 33250A for a 5-kHz sine wave and applied it to the new input. Looking at both the 33250A and the Wien-bridge outputs with an oscilloscope, I slowly dialed up the 33250A frequency and was thrilled to finally see the sinusoids come “close” and then snap into lock. DIANE 38 EDN EuropE | december 2012 www.edn-europe.com http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE December 2012

Cover
Contents
Texas Instruments Europe
Microchip
Digi-Key
Masthead
EDN comment
Pulse
Digi-Key
Baker’s Best
Embedded World 2013
Test & Measurement World
Rohde & Schwarz
Digi-Key
Squeezing the most from battery cells with a switched-mode pump
Signal integrity
Processor architectures : one to rule them all ?
Digi-Key
Mechatronics in Design
Advances in wireless speaker performance and technology
Design Ideas
Teardown; the ultimate Consumer Product ?
Product roundup
Tales from the Cube

EDNE December 2012

EDNE December 2012 - Cover (Page 1)
EDNE December 2012 - Contents (Page 2)
EDNE December 2012 - Texas Instruments Europe (Page 3)
EDNE December 2012 - Microchip (Page 4)
EDNE December 2012 - Digi-Key (Page 5)
EDNE December 2012 - Masthead (Page 6)
EDNE December 2012 - EDN comment (Page 7)
EDNE December 2012 - Pulse (Page 8)
EDNE December 2012 - Pulse (Page 9)
EDNE December 2012 - Pulse (Page 10)
EDNE December 2012 - Digi-Key (Page 11)
EDNE December 2012 - Digi-Key (Page 12)
EDNE December 2012 - Digi-Key (Page 13)
EDNE December 2012 - Baker’s Best (Page 14)
EDNE December 2012 - Embedded World 2013 (Page 15)
EDNE December 2012 - Test & Measurement World (Page 16)
EDNE December 2012 - Rohde & Schwarz (Page 17)
EDNE December 2012 - Rohde & Schwarz (Page 18)
EDNE December 2012 - Digi-Key (Page 19)
EDNE December 2012 - Digi-Key (Page 20)
EDNE December 2012 - Squeezing the most from battery cells with a switched-mode pump (Page 21)
EDNE December 2012 - Squeezing the most from battery cells with a switched-mode pump (Page 22)
EDNE December 2012 - Squeezing the most from battery cells with a switched-mode pump (Page 23)
EDNE December 2012 - Squeezing the most from battery cells with a switched-mode pump (Page 24)
EDNE December 2012 - Signal integrity (Page 25)
EDNE December 2012 - Processor architectures : one to rule them all ? (Page 26)
EDNE December 2012 - Processor architectures : one to rule them all ? (Page 27)
EDNE December 2012 - Processor architectures : one to rule them all ? (Page 28)
EDNE December 2012 - Digi-Key (Page 29)
EDNE December 2012 - Digi-Key (Page 30)
EDNE December 2012 - Digi-Key (Page 31)
EDNE December 2012 - Digi-Key (Page 32)
EDNE December 2012 - Mechatronics in Design (Page 33)
EDNE December 2012 - Advances in wireless speaker performance and technology (Page 34)
EDNE December 2012 - Advances in wireless speaker performance and technology (Page 35)
EDNE December 2012 - Advances in wireless speaker performance and technology (Page 36)
EDNE December 2012 - Design Ideas (Page 37)
EDNE December 2012 - Design Ideas (Page 38)
EDNE December 2012 - Design Ideas (Page 39)
EDNE December 2012 - Design Ideas (Page 40)
EDNE December 2012 - Teardown; the ultimate Consumer Product ? (Page 41)
EDNE December 2012 - Product roundup (Page 42)
EDNE December 2012 - Product roundup (Page 43)
EDNE December 2012 - Tales from the Cube (Page 44)
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