Rapid engineering prototypes are real circuits that Maxim application engineers have built and measured in our labs. They can provide a starting point for new RF designs.
Objective: To modify the MAX3509 upstream CATV amplifier for higher output.
Many producers of cable telephony require a high output upstream amplifier to overcome coupler loss. Manufacturers may need 67dBmV to 68dBmV at the amplifier output to overcome duplexer and coupler losses. By using a 1:2 (voltage) step-up output transformer and series output resistance of 35.5 Ω, the MAX3509 can offer good on state return loss and still meet DOCSIS off-state return loss after duplexer and coupler. A typical system can have a 1dB loss at the duplexer and a 6dB loss at the coupler for a total loss, after D.U.T., of 7dB.
The MAX3509 is a cable upstream amplifier which operates over a 5MHz to 65MHz frequency range. It features variable gain control (VGA) by a 3-wire digital serial bus in 1dB steps. It offers low-impedance op-amp outputs which permit flexibility in output match and drive levels. The MAX3509 can output up to 66dBmV QPSK through a 1:1 transformer. It also offers a transmit-disable mode and a power-down mode. It is available in a 20-pin TSSOP-EP package for the extended–industrial range (-40°C to +85°C).
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