Solid State

Solid State

MicroTechnology

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DUAL LINEAR-ANTILOG VOTTAGE CONTROLLED AMPLIFIER

D E S C R I P T I O N

T h e S S M 2 0 2 2 i s a l o w c o s t , h i g h p e r f o r m a n c e , d u a l v o l t a g e - c o n t r o l l e d a m p l i f i e r d e s i g n e d f o r e a s y u s e i n p r o g r a m - a b l e e l e c t r o n i c m u s i c s y s t e m s , a n d a s a g e n e r a l p u r p o s e g a i n c o n t r o l e l e m e n t . O n - c h i p c o n t r o l a m p l i f i e r s h a v e

b e e n p r o v i d e d f o r e a c h c h a n n e l f o r i n d e p e n d e n t l i n e a r o r a n t i l o g g a i n c o n t r o l . T h e s i g n a l a n d l i n e a r c o n t r o l i n p u t s a r e c u r r e n t s u m m i n g n o d e s a n d c u r r e n t o u t p u t s a l l o w f o r s u m m i n g b y s i m p l e c o n n e c t i o n . T h e s i g n a l c h a n n e l s o f f e r lo w n o i s e , l o w d i s t o r t i o n , w i d e b a n d w i d t h , a n d l o w c o n t r o l f e e d t h r o u g h . T h e d e v i c e r e q u i r e s f e w e x t e r n a l c o m p o n e n t s t o i m p l e m e n t i t s b a s i c f u n c t i o n ,

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T h e fi g u r e a b o v e s h o w s t h e ty p i c a l c o n n e c t i o n o t l h e 2 0 2 2 a s a d u a l V C A . T h e s i g n a l i n p u t ( s ) , p r n s 2 n d 1 5 , a r e v t r t u a l g r o u n d s u m m i n g n o d e s . T h e r e f e r e n c e c u r r e n t e s t a b l i s h e d a t p i n 1 d e l e r m i n e s t h e le v e l a t w h i c h t h e in p u t s i g n a l w i l l c l i p . W i t h re f e r e n c e c u r r e n t o f 0 . 8 m A t h i s w i l l b e 2 0 0 u A T h e in p u t r e s i s l o r ( s ) s h o u l d b e c h o s e n t o g i v e a * 1 0 0 u A s i g n a l c u r r e n t a t t h e in p u t v o l t a g e peaks. The 75K resistor shown will satisfy this condition for a * 75 signal wrth clipping taking place at twice this level: the maximum voltages available from r 15V supplies The offset,'control leedthrough adjustment is required only for precision applications or to null offsets generated rn previous stages.

The output current(s) at pins 3 and 4 is converted to a voltage with the op amp, resistor-network shown. 75K will give unity gain tor a c o n t r o l c u r r e n l o J 2 0 0 u A . l c , th e o u t p u t o f t h e o n - c h i p c o n t r o l c i r c u i t , i s p r o p o r t i o n a l t o th e p r o d u c l o f t h e li n e a r c o n t r o l c u r r e n t ( s ) , pins 6 and .11,

and the negative exponent of the voltage at lhe exponential control pins: 7 and 10. For best distortion and control currenl feedthrough performance, the maximum control current should be in the 200 to 400uA range.

T h e l i n e a r c o n t r o l i n p u l s a r e v i r t u a l g r o u n d s u m m i n g n o d e s . T h e s e n s e o f t h e c o n t r o l ( s ) i s f r o m g r o u n d u p , w i t h th e o u l p u t ( s ) g o i n g t o z e r o w i l h g r o u n d a t t h e c o r r e s p o n d i n g c o n l r o l i n p u t . T h e l i n e a r c o n t r o l r e s i s t o r ( s ) a b o v e w i l l g i v e 2 0 0 u A f o r a + 1 5 V control voltage. The exponential control input attenuator can be designed for a wide range of conlrol sensitivities and input voltage ranges. In all cases the minimum voltage will give maximum gain and the maximum voltage will give maximum attenuation. The input attenuator(s) shown will control the gain of the channel(s) over a 100db range for an input voltage of 0 to + 10 volts. Other sensitivities and input voltage ranges can be easily accommodated by changing the attenuation factor and the current at the linear i n p u t p i n ( s ) .

The 100pf , 100O, 4700pt networks provide feedforward compensalion of the on-chip control op amps. With these values one can achieve a 1 MHz bandwidth for the signal channel. The actual bandwidth one will realize will be determined by the slew rate and small signal bandwidth of the op amp in the output current of voltage conventors,

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