Electronic device
An electronic device satisfies: f LO =N×f clk . . . (1); and (N−1)×f clk <fD 1 <N×f clk <fD 2 <(N+1)×f clk . . . (2), where: f LO represents a frequency of the local oscillator signal; N represents an integer; fD 1 represents a lower limit frequency of the received signal; and fD 2 represents an upper limit frequency of the received signal. Even if harmonic components, whose respective frequencies are respective integral multiples of the clock frequency f clk , are mixed as spurious components into a path for a target signal, the harmonic spurious components do not fall within the target wave spectrum observed after the frequency conversion by the mixer. Thus, it is possible to prevent deterioration in reception performance, the deterioration being caused by in-band spurious components arising from higher harmonic waves whose frequencies are respective integral multiples of a clock frequency f clk .
1. An electronic device comprising:
a direct conversion receiver; and
a clock synchronization circuit which operates in synchronization with a clock signal having a clock frequency f clk ,
the direct conversion receiver including:
a frequency converter circuit for carrying out a frequency conversion by mixing a received signal and a local oscillator signal so as to convert the received signal into a baseband signal; and
a direct-current offset canceller circuit for removing a direct-current offset contained in a signal which has been subjected to the frequency conversion by the frequency converter circuit,
said electronic device selecting, according to a lower limit frequency fD 1 and an upper limit frequency fD 2 of the received signal, a value for an integer N or a value for the clock frequency f clk so as to satisfy:
f LO =N×f clk (1); and
( N− 1)× f clk <fD 1 <N×f clk <fD 2<( N+ 1)× f clk (2),
where f LO represents a frequency of the local oscillator signal.
2. The electronic device according to claim 1 , wherein the N is equal to 1.
3. The electronic device according to claim 1 , wherein the clock synchronization circuit is a digital circuit.
4. The electronic device according to claim 1 , wherein the clock synchronization circuit is a switched capacitor circuit.
5. The electronic device according to claim 1 , the clock synchronization circuit includes a digital circuit and a switched capacitor circuit.
6. The electronic device according to claim 1 , wherein:
the frequency f LO of the local oscillator signal is changed; and
the clock frequency f clk is selected so that the Formulae (1) and (2) are satisfied.
7. The electronic device according to claim 1 , further comprising:
an oscillator for outputting the local oscillator signal having the frequency f LO ; and
a frequency divider for dividing by N the local oscillator signal so as to output the clock signal having the clock frequency f clk .
8. The electronic device according to claim 1 , wherein the frequency converter circuit and the clock synchronization circuit are fabricated so as to constitute a single integrated circuit.
9. The electronic device according to claim 1 , wherein the frequency converter circuit and the clock synchronization circuit are fabricated in a single package.
10. The electronic device according to claim 1 , wherein the frequency converter circuit and the clock synchronization circuit are mounted on a single printed circuit board.
11. The electronic device according to claim 1 , wherein:
the received signal is a digitally modulated signal; and
a circuit which operates in synchronization with the clock signal is a demodulation circuit for demodulating the digitally modulated signal.
12. The electronic device according to claim 1 , wherein each of the frequency converter circuit and a digital circuit which operates in synchronization with the clock signal having the clock frequency f clk is used to carry out another function different from a function of the direct conversion receiver.
13. The electronic device according to claim 1 , wherein the frequency converter circuit and a digital circuit which operates in synchronization with the clock signal having the clock frequency f clk are used to carry out a single function in combination.
14. The electronic device according to claim 1 , wherein the frequency converter circuit is used to carry out a receiving function.