The TV amplifier has been tuned under class-A small-signal conditions and characterised under large signal class-AB conditions from band IV - V in UHF. (All Datasheets)Amplifier Circuit
The total description of the amplifier is given in Figs 6 and 7 and Table 8 (in datasheet). The amplifiers input and output matching networks contain mixed microstrip-lumped elements networks to transform the terminal impedance levels to approx. 25 W balanced.
The remaining transformation to 50 W unbalanced is obtained by 1 : 2 balun transformers. The baluns B1 and B2 are 25 W semi-rigid coax cables with an electrical length of 45° at midband and a diameter of 1.8 mm, soldered over the whole length on top of microstrip lines. To keep the circuit in balance two stubs L1 and L8 with the same length have been added. For low frequency stability enhancement the input balun stubs are connected to the bias point by means of 1 W series resistors. Large capacitors (C4 and C11) are added at the biasing points to improve the amplifiers video response.
Printed Circuit Board (PCB)
The printed-circuit board laminate utilised is PTFE-glass with an er = 2.55 and a thickness of 0.51 mm (20 mills).
A complete TV transmitter and amplifier has been designed and characterised based on the BLV861, capable of operating in full band IV and V with flat gain and high output power in class-AB. BLV861 is able to generate 100 W CW power and a power gain compression below 1 dB in band IV and V. Overall gain of the amplifier is >8.5 dB and an efficiency of ± 55%. TV-measurements have been carried out showing a 1 dB compression point above 120 W PO, SYNC at VCE = 28 Vand 150 W at VCE = 32 V.
- Amplifier shows an agreed linearity performance in class AB operation both under two tone and three tone conditions.
- Biasing the amplifier at a VCE = 32 V results in a higher output peak sync power and a better linearity response.
See more : FM Stereo Transmitter - TV Transmitter - FM Stereo Encoder
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