Receiver circuit

Abstract

In double-conversion receiver circuits, higher harmonics of a first local oscillating signal SLO1 and higher harmonics of a second local oscillating signal SLO2 enter a mixing circuit that converts a first intermediate frequency IF1 into a second intermediate frequency IF2, resulting in problems in that frequency IF2 signal components that are generated by the mixture of the two signals cause decreased sensitivity. As a countermeasure, an LPF 78 is provided between a second mixer circuit 60 and a divide-by-two frequency divider circuit 76 that supplies the signal SLO2 to the second mixer circuit 60. The LPF 78 removes the higher harmonic components of the signal SLO2 that may be generated in the divide-by-two frequency divider circuit 76. Even when higher harmonic components of the signal SLO1 that may be generated in a divide-by-n frequency divider circuit 72 enter the second mixer circuit 60 through the semiconductor substrate and the like, the higher harmonic components of the second local oscillating signal SLO2 are not mixed in, and the occurrence of signal components of the frequency IF2 that result from higher harmonics being mixed in can thereby be prevented.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that shows the circuit configuration of a conventional double-conversion AM-radio receiver; and

FIG. 2 is a block diagram that shows an abbreviated circuit configuration of a double-conversion AM-radio receiver that is an embodiment of the present invention.

Claims

1. A double-conversion receiver circuit comprising: a first local oscillator for generating a first local oscillating signal;a first mixer circuit for mixing the first local oscillating signal and a received signal having a radio frequency, and generating a first intermediate frequency signal;a second local oscillator for generating a second local oscillating signal; anda second mixer circuit for mixing the first intermediate frequency signal and the second local oscillating signal, and generating a second intermediate frequency signal, whereinthe first local oscillator has:a first oscillator circuit for generating a first primary oscillating signal; anda first frequency divider circuit for dividing the first primary oscillating signal and generating the first local oscillating signal, and whereinthe second local oscillator has:a second oscillator circuit for generating a second primary oscillating signal;a second frequency divider circuit for dividing the second primary oscillating signal and generating the second local oscillating signal; anda frequency filter that is connected to an output terminal of the second frequency divider circuit and that minimizes passage to the second mixer circuit of a signal component that is at or above a prescribed cut-off frequency.

2. The receiver circuit according to claim 1, wherein the frequency filter is a low-pass filter for minimizing a higher harmonic component of the second local oscillating signal that is generated in the second frequency divider circuit.

3. The receiver circuit according to claim 1, wherein the receiver circuit is an integrated circuit formed on a shared semiconductor substrate.

4. A double-conversion receiver circuit comprising: a first local oscillator for generating a first local oscillating signal;a first mixer circuit for mixing the first local oscillating signal and a received signal having a radio frequency, and generating a first intermediate frequency signal;a second local oscillator for generating a second local oscillating signal; anda second mixer circuit for mixing the first intermediate frequency signal and the second local oscillating signal, and generating a second intermediate frequency signal, whereinthe first local oscillator has:a first oscillator circuit for performing PLL control using as a reference a reference oscillating signal that is generated based on an original oscillating signal having a frequency that is higher than the second intermediate frequency signal, and generating a first primary oscillating signal; anda first frequency divider circuit for dividing the first primary oscillating signal and generating the first local oscillating signal, and whereinthe second local oscillator has:a second oscillator circuit for generating a second primary oscillating signal having a frequency that corresponds to the original oscillating signal, which is input to the second oscillator circuit;a second frequency divider circuit for dividing the second primary oscillating signal and generating the second local oscillating signal; anda frequency filter that is connected to an output terminal of the second frequency divider circuit and that minimizes passage to the second mixer circuit of a signal component that is at or above a prescribed cut-off frequency.

5. The receiver circuit according to claim 4, wherein the frequency filter is a low-pass filter for minimizing a higher harmonic component of the second local oscillating signal that is generated in the second frequency divider circuit.

6. The receiver circuit according to claim 4, wherein the receiver circuit is an integrated circuit formed on a shared semiconductor substrate.

7. The receiver circuit according to claim 4, wherein the second primary oscillating signal is input from the second oscillator circuit to the first oscillator circuit as the reference oscillating signal.