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CATHODE FOLLOWER EQUATIONS

 The cathode follower is an  amplifier ( with  an  amplification  less  than
unity ) that has  its  output signal  taken  between  cathode  and   ground.
To obtain a cathode follower from Fig. 2-1, the resistance  of  R_L  is  set
equal to zero  and  the bypass capacitor across R_k2   is removed.  The  cir-
cuit equations then are, for the voltages:

                      e_g = e_s - e_k = e_s - ( i_p* R_k )

and

                             e_p = -e_k

where R_k is the sum of R_k1 and R_k2. Substitution in Equation 4  gives
the amplification equation:
 

              K = e_k/e_s = ( g_m* R_k ) / [ 1 + ( g_m+ g_p ) R_k ]              (11)
 

  The equation for the amplification of a pentode cathode  follower  is
derived in a similar manner; using the  same  assumptions  as  made  on
page 8, it is:
 

                             K = ( g_m1* R_k ) / [ 1 + ( g_m1* R_k ) ]                   (12)
 

and substituting for the pentode parameters:
 

                             K = ( G_m1* X_p* R_k ) / [ 1 + ( G_m1* X_p* R_k ) ]         (13)
 
 
 
 
 
 
 
 
 

                                                                                                                   9

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Copyright 2008 for Phyllis K. Pullen, M.D.,
by Robert J. Legg