Substituting THAT and 2181-Series VCAs for THAT 2150-Series VCAs in Existing Designs Abstract

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Belinda Simpson
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1 THAT Corporation Design Note Substituting THAT 0- and -Series VCAs for THAT 0-Series VCAs in Existing Designs Abstract THAT Corporation s 0- and -series VCAs are pin-for-pin compatible, improved performance replacements for the 0-series VCAs. Designers may convert existing 0-series designs to use the 0/ VCAs without making any changes to existing PCB layouts. This application note details the few component value changes and component deletions required to obtain optimum performance with the 0- and -series VCAs in existing 0-series designs. Choosing the correct VCA Table shows the correct VCA to use when switching from a THAT 0-series part to one of the THAT x-series. When retrofitting the x VCAs, designers may replace the x-series VCA with a trimmable VCA or a trimless VCA. For high performance applications, the choice is normally to choose a trimmable Lx or Sx. However, where distortion performance is less critical and trim-free production is a goal, the 0Lx is the right choice. Old VCA Precision Trimless THAT THAT LC or THATSC THAT 0LC THAT 0A THAT LB or THATSB THAT 0LB THAT THAT LA or THATSA THAT 0LA Table 0 Series The 0-series VCAs are pre-trimmed at wafer stage for low THD and control-voltage feedthrough without further adjustment. The parts are available in three grades (0LA, 0LB, and 0LC) selected for factory-trimmed distortion performance, allowing the user to optimize cost vs. performance. Figure shows a typical 0-series application circuit in which the negative control port (pin ) is used for gain control. Components R, R, and VR provide for external adjustment of VCA symmetry. Figure shows the same circuit adapted for use with a 0-series VCA. Note that external symmetry trim components R, R, and VR have been deleted. In particular, R must not be used with the 0 Series it will upset the internal symmetry trim. Capacitor C may be reduced in value to as low as pf in order to increase the circuit bandwidth if desired. Figures and show similar 0-series application circuits wherein the positive control port (pins and ) or both control ports are used, respectively. Figures and show the 0-series counterparts to these circuits. Copyright 00 by THAT Corporation. All rights reserved. Document 000 Rev 00

2 THAT Corporation Design Note Substituting the x for the x Table summarizes the component deletions required to convert a typical 0 application to the 0-series. External 0 Series 0 Series Component 0A 0A 0B 0C R DELETE DELETE DELETE R 0k 90k 00k DELETE DELETE DELETE VR 0k 0k 0k DELETE DELETE DELETE Table Series The -series VCAs are selected after packaging primarily on the basis of externally trimmed THD and control-voltage feedthrough performance. The parts are selected into three grades (A, B, and C) based on 00% tested performance after external trim. External trimming of VCA symmetry allows higher performance than can be consistently obtained with pretrimmed parts. Both SIP (L designation) and SO- (S designation) packages are available in the -series. Of course, since the 0-series was only available in SIP, only that package applies to the retrofit situation. Figures,, and 9 illustrate typical application circuits utilizing the negative, positive, and both control ports respectively. Note that the external trim potentiometer VR, and its wiper resistor R are present as in the 0 circuits, but that R is deleted. R is not required because there is an internal ohm resistor between pins and in all -series VCAs. The values shown for R are scaled differently, based on +/- V supplies, for each of the three grades of these parts. As with the 0-series circuits, C may be reduced to as low as pf if desired. Table summarizes the component value changes required to convert 0-series circuits to utilize the -series VCAs (assuming = +V, = -V, see the datasheet to calculate R values for other supply voltages). External Component 0 Series Series 0A A B C R DELETE DELETE DELETE R 0k 90k 00k 0k 0k 0k VR 0k 0k 0k 0k 0k 0k Table THAT Corporation Sumner Street, Milford MA 0- Tel: + (0) -900 Fax: + (0) info@thatcorp.com Web:

3 THAT Corporation Design Note Substituting the x for the x VR 0k 0A-90k -0k -00k R C 00n R R R C u R 0A, or U k C p UA 0 Figure. Typical 0-series application circuit with Ec- driven C 00n R C u R 0A, 0B or 0C k U C p UA 0 Figure. Typical 0-series application circuit with Ec- driven Copyright 00 by THAT Corporation. All rights reserved. Document 000 Rev 00

4 THAT Corporation Design Note Substituting the x for the x VR 0k C u 0A-90k -0k -00k R R 0A, or R R C 00n k U C p R UA 0 Figure. Typical 0-series application circuit with Ec+ driven C C u R 0A, 0B or 0C 00n k U C p R UA 0 Figure. Typical 0-series application circuit with Ec+ driven THAT Corporation Sumner Street, Milford MA 0- Tel: + (0) -900 Fax: + (0) info@thatcorp.com Web:

5 THAT Corporation Design Note Substituting the x for the x 0A-90k -0k -00k VR 0k R C 00n C u Pos. R 0A, or R R k U R C p UA 0 Neg. Figure. Typical 0-series application circuit with both control pins driven C 00n R Pos. C u R 0A, 0B or 0C k U C p UA 0 Neg. Figure. Typical 0-series application circuit with both control pins driven Copyright 00 by THAT Corporation. All rights reserved. Document 000 Rev 00

6 THAT Corporation Design Note Substituting the x for the x VR 0k A-0k B-0k C-0k R C 00n R C u R A, B or C k U C p UA 0 Figure. Typical -series application circuit with Ec- driven VR 0k A-0k B-0k C-0k R C 00n R C u R A, B or C k U C p UA 0 Figure. Typical -series application circuit with Ec+ driven THAT Corporation Sumner Street, Milford MA 0- Tel: + (0) -900 Fax: + (0) info@thatcorp.com Web:

7 THAT Corporation Design Note Substituting the x for the x VR 0k A-0k B-0k C-0k R C 00n R Pos. C u R A, B or C k U C p UA 0 Neg. Figure 9. Typical -series application circuit with both control pins driven Copyright 00 by THAT Corporation. All rights reserved. Document 000 Rev 00

8 THAT Corporation Design Note Substituting the x for the x Notes: THAT Corporation Sumner Street, Milford MA 0- Tel: + (0) -900 Fax: + (0) info@thatcorp.com Web:

GR16. Technical Manual. 10 M SPS, 16-bit Analog Signal Digitizer up to 8MB FIFO

GR16. Technical Manual. 10 M SPS, 16-bit Analog Signal Digitizer up to 8MB FIFO GR M SPS, -bit Analog Signal Digitizer up to MB FIFO Technical Manual 90 th Street, Davis, CA 9, USA Tel: 0--00 Fax: 0--0 Email: sales@tern.com web site: www.tern.com COPYRIGHT GR, EL, Grabber, and A-Engine