Filter circuitry

Circuitry for use in a direct conversion transmitting chain, the circuitry comprising:

• mixing circuitry configured to upconvert base band signals to provide radio frequency signals;
• amplifying circuitry configured to amplify radio frequency signals;
• and
• filtering circuitry connected between the mixing circuitry and the amplifying circuitry, the filtering circuitry comprising
• a first connection configured to be connected to a signal line carrying varying signal voltage;
• a second connection;
• a first circuit portion comprising a parallel resonant circuit, the parallel resonant circuit comprising a variable capacitance connected in parallel with a first inductor;
• and
• a second circuit portion comprising a second inductor, wherein
• the first circuit portion and the second circuit portion are connected in series between the first connection and the second connection, and
• a ratio n of a first inductance of the first inductor to a second inductance of the second inductor satisfies n=(H2−1)−1, where H is an integer and n is a fraction.

Circuitry comprising:

• a first connection configured to be connected to a signal line carrying varying signal voltage;
• a second connection;
• a first circuit portion comprising a parallel resonant circuit, the parallel resonant circuit comprising a variable capacitance connected in parallel with a first inductor;
• and
• a second circuit portion comprising a second inductor, wherein
• the first circuit portion and the second circuit portion are connected in series between the first connection and the second connection, and
• a ratio n of a first inductance of the first inductor to a second inductance of the second inductor satisfies n=(H2 −1)−1, where H is an integer and n is a fraction.