This device is a programmable 3-band mixer oscillator and synthesizer intended for LOW, MID and HIGH band TV and VCR tuners. It has three double balanced mixers and three oscillators for the LOW, MID and HIGH band respectively, a PLL synthesizer, and an IF amplifier. There are four package variants: TDA6508, TDA6509, TDA6508A and TDA6509A. Versions TDA6508; TDA6509 have a symmetrical IF amplifier; versions TDA6508A; TDA6509A have an asymmetrical IF amplifier, (see Fig.1).

The common output of all three mixers can be connected, via two output pins, to an external IF filter to enable shunted IF bandpass and/or serial filtering for improved signal handling. Two input pins are available for connecting the output of the external filter to the input of
the IF amplifier. The mixer output has an impedance of 300Ω. The IF amplifier input has an impedance of 2.5 kΩ(5 pF).