Low-Cost Quad Op Amp Drives RF Modulator

Posted on Feb 6, 2014

The video circuit illustrated in Figure 1 combines an audio-subcarrier notch filter and group-delay equalization as required by the ITU-470 standard. It also includes an amplitude-adjustment capability for driving an RF video modulator in NTSC applications. (PAL operation requires a minor adjustment of the filter and all-pass values. ) For best per

Low-Cost Quad Op Amp Drives RF Modulator
Click here to download the full size of the above Circuit.

formance, the input should be driven from a low-impedance source, such as an op amp or active filter. Two second-order all-pass stages (U1a, R1, C1, L1 and U1c, R13, C3, L3) and a first-order all-pass stage (U1d, C4, R14) form a fifth-order group-delay equalizer that compensates for group delay introduced by the notch filter (U1b, R6, C2, L2). Potentiometer R7 adjusts the output amplitude as required by the modulator in use. The notch frequency is set by L2 and C2, and the notch depth and bandwidth are set by R4, R5, and R6. Typical notch depth is greater than ­16 dB ( Fig. 2 ). Flatness above 2. 5 MHz is ±0. 5 dB.

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    Temperature Controlled Relays 4001/4011
    Over-Under Voltage Cut-Out with 555
    Autonomous Parallel Parking RC Car
    Modular Music Box Arduino polyphonic audio
    Capacitive liquid level sensor circuit
    Time Switch
    Portable alcohol detector alarm circuit
    The PC CPU overheating language caution circuit diagram