832 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



about 1 db at frequencies up to 10 mc. Comparison of the measured and 

 computed values is shown on Fig. 15 for a load of 500 ohms with no 

 high-frequency compensation. The low-frequency gain is higher than 

 for the common base connection but the response is down 3 db at 7 mc. 

 By using the combination of Ri in parallel with 800 nnf in the emitter 

 circuit, negative feedback is introduced at low frequencies which results 

 in the reduction of low frequency gain tending to make the response 

 more uniform. In addition the L-C network has been added in the output 

 to compensate for the drop of | /i2i | with increasing frequency and the 

 increasing effect of the output capacitance. 



This results in the response shown as the dotted curve on Fig. 15. The 

 low-frequency gain has been reduced to 17.5 db, but the response is now 

 flat to within dzO.3 db up to 13 mc and is 3 db down at 18 mc. 



Although the data given on video amplifiers shows the results ob- 

 tained using one transistor, similar response curves were obtained from 

 some 6 or 8 units. 



An I-F Amplifier Centered at 30 Mc. 



The design of an IF amplifier at 30 mc is distinct from the preceding 

 two cases in that one can use matching techniques over the narrow band. 



Reference to Table 1 reveals that the common-base connection pro-, 

 vides more potential gain at 30 mc than the common emitter connection; 

 in fact, the common-base connection can be made to oscillate with 

 certain terminations. The common-base connection is chosen for the 

 30-mc amplifier. 



Vc = 1 V 



11-13yUH 



5-25/U/J-F 



^^ 



■5oon 



OUT- 

 PUT 



i 



+ 10.5V 



i-7.5 V 



Fig. 14 — Circuit of a common emitter video amplifier. 7?i in parallel with 

 800 pLui and the LC network in the output circuit peak the response at 10 to 12 

 mc. 



