A tunable notch filter for the front end of an RF receiver includes magnetically coupled input and output tunable stages each responsive to a tuning voltage provided thereto. Each of the input and output stages includes a respective series and parallel resonant circuit wherein the parallel resonant circuits are tuned to a selected RF frequency and the series resonant circuits are tuned to a frequency approximately equal to that of a local oscillator. By using the series resonant circuits to create a notch at a frequency approximating that of the local oscillator, conducted local oscillator leakage from the receiver's antenna is substantially reduced and local oscillator image frequency rejection is substantially improved.

Tunable notch filter for image frequency and conducted local oscillator leakage rejection

A 3-element series parallel resonator, which performs series resonance and parallel resonance at a predetermined frequency by a combination of three elements including an inductor and a capacitor of concentrated constants, is used as a filter. This design can reduce the circuit constant and permits a filter to be formed on a semiconductor substrate. Accordingly, various micro-wave devices, such as an amplifier which requires a filter, a frequency converter, a multiplier and signal switcher, can be designed into an MMIC on a single chip.

Semiconductor device with a filter formed of 3-element series-and-parallel resonators

Parallel and series tuned resonator circuit topologies are disclosed that permit implementation of narrow band-pass filters having high loaded Q and optimal coupling (for low insertion loss) at frequencies in approximately the 50 MHz to 1 GHz. The topologies employ an additional series capacitor for the parallel-tuned topology, and an additional series capacitor for the series-tuned topology, the capacitors having values counterintuitive to those of skill in the art to produce 6th order transfer functions out of what were once lower order resonators. Multistrip transmission lines are exploited in the parallel-tuned circuit to reduce the inductance of the resonators to achieve a very large skew in the ratios of inductance to capacitance, to increase Q while maintaining optimal coupling between the resonators of the tuned resonator circuits. Air coils are used in the series-tuned topology to achieve the large inductor values desirable for this topology.

Magnetically coupled resonators for achieving low cost narrow band pass filters having high selectivity, low insertion loss and improved out-of-band rejection

The invention relates to a circuitry arrangement by means of which it is possible to suppress frequency components which cause spurious response in the intermediate frequency amplifier in a radio telephone receiver. The amplifier produces not only the input signal frequency but also harmonic frequencies of this frequency, in which case some harmonic frequency of the frequency component which causes spurious response is the same as the intermediate frequency. In the circuitry, between the signal path and the circuit ground, there is a circuit which is in series resonance at the frequency of the frequency component which causes spurious response, in which case a signal of this frequency is strongly attenuated, and the circuit is in parallel resonance at the intermediate frequency, in which case attenuation of a signal of this frequency is slight. It is possible to select an intermediate-frequency which is lower than the reception band multiplied by two, so that even strict requirements set on spurious response can be satisfied.

Circuitry arrangement for the elimination of spurious response in a radio telephone receiver

A tunable filter (100) is provided including a first resonator (110) and a second resonator (120). The bandwidth of the tunable filter is maintained constant by providing purely inductive coupling (114) between the first and the second resonators (110 and 120). The first and the second resonators (110 and 120) include tuning elements (108-109 and 118-119) which are second coupled to each other by means of a capacitor (130) to improve image rejection performance of the tunable filter (100).

Tunable filter having capacitively coupled tuning elements

In a superheterodyne receiver, such as a typical television receiver, a radio frequency coupling arrangement includes a first resonant circuit coupled to receive the input signal and further coupled to a second resonant circuit by a first coupling. Both resonant circuits are tuned to the desired signal frequency. The capacitive branch of the first resonant circuit includes a circuit impedance for providing a neutralizing voltage, at least a portion of which is coupled by a second coupling to the inductive branch of the second resonant circuit. The circuit impedance is selected to cause cancellation in the inductive branch between image frequency components coupled by the first coupling and image frequency components coupled by the second coupling, without substantially affecting the desired signals.

Hettiger James

Papers

Tracking image frequency trap

Frequency selective network

Piege de frequence image suivant les variations d'accord