AN-763 APPLICATION NOTE One Technology Way P.O. Box 9106 Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 Fax: 781.461.3113 www.analog.com Dual Universal Precision Op Amp Evaluation Board INTRODUCTION The EVAL-PRAOPAMP-2RZ, EVAL-PRAOPAMP-2RMZ, and Since the common-mode voltage into the amplifier varies EVAL-PRAOPAMP-2CPZ are universal precision evaluation with the input signal in the KRC filter circuit, a high CMRR boards that accommodate dual op amps in 8-pin SOIC, amplifier, such as the ADA4077-2, is required to minimize MSOP, and LFCSP packages, respectively. For the exposed pad distortion. Furthermore, the low offset voltage of the ADA4077-2 connection for the LFCSP package, see the appropriate product allows a wider dynamic range when the circuit gain is chosen to data sheet. be high. These PRAOPAMP evaluation boards provide multiple choices The circuit shown in Figure 1 consists of two stages. The first and extensive flexibility for different application circuits and stage is a simple high-pass filter with a corner frequency, fC, of configurations. 1 (1) These boards are not intended to be used with high frequency 2 C1C2R1R2 components or high speed amplifiers. However, they provide and the user with many combinations for various circuit types, R1 including active filters, instrumentation amplifiers, composite Q = K (2) amplifiers, and external frequency compensation circuits. R2 Several examples of application circuits are provided in this where K is the dc gain. application note. Choosing equal capacitor values minimizes the sensitivity and TWO STAGE BAND-PASS FILTER simplifies the expression for f to C C3 680pF 1 R2 (3) 10k 2C R1R2 V The value of Q determines the peaking of the gain vs. frequency V 2 4 (generally ringing in the time domain). Commonly chosen R3 R4 6 1 4 V C2 C1 33k 33k OUT 7 3 10nF 10nF values for Q are near unity. 8 1/2 ADA4077-2 5 8 1/2 ADA4077-2 C4 + Setting Q = 1/2 yields minimum gain peaking and minimum V+ 330pF R1 V1 V+ 20k ringing. Use Equation 3 to determine the values for R1 and R2. For example, set Q = 1/2 and R1/R2 = 2 in the circuit example, Figure 1. KRC Filter and pick R1 = 5 k and R2 = 10 k for simplicity. The second stage is a low-pass filter whose corner frequency can be deter- The low offset voltage and high CMRR makes the ADA4077-2 mined in a similar fashion. a great choice for precision filters, such as the KRC filter shown in Figure 1. R3 = R4 = R This particular filter implementation offers the flexibility to 1 f = C tune the gain and the cut-off frequency independently. 2 R C3C4 and C3 Q = 1/2 C4 Rev. C Page 1 of 8 05284-001AN-763 Application Note TABLE OF CONTENTS Introduction ...................................................................................... 1 High Gain Composite Amplifier .....................................................3 Two Stage Band-Pass Filter ............................................................. 1 External Compensation Techniques ...............................................4 Revision History ............................................................................... 2 Snubber Network ...............................................................................5 Half Wave, Full Wave Rectifier ....................................................... 3 REVISION HISTORY 10/13Rev. B to Rev. C Updated Format .................................................................. Universal Replaced All Figures ......................................................................... 1 Changed EVAL-PRAOPAMP-2R/2RU/2RM to EVAL- PRAOPAMP-2RZ, EVAL-PRAOPAMP-2RMZ, and EVAL- PRAOPAMP-2CPZ Throughout .................................................... 1 Deleted Authors Names and added Introduction Section Heading .............................................................................................. 1 Changes to Two Stage Band-Pass Filter Section ........................... 1 Changes to Half Wave, Full Wave Rectifier Section ..................... 3 Changes to High Gain Composite Amplifier Sections ................ 3 Rev. C Page 2 of 8