Receiver digital-analog converter and tuning circuit
An object of the present invention is to provide a receiver, a digital-analog converter and a tuning circuit in which temperature compensating components can be formed on a semiconductor substrate while reducing component costs. An FM receiver 100 is constituted by including an antenna 1 , a high frequency receiving circuit 2 , a local oscillator 3 , two digital-analog converters (DACs) 4, 6 , a control section 8 , a mixing circuit 9 , an intermediate frequency amplification circuit 10 , a detection circuit 11 , a low frequency amplification circuit 12 and the speaker 13 . The DACs 4, 6 have a predetermined temperature coefficient, of which output voltage is changed in accordance with ambient temperature. When a characteristic of VCO 31 is changed with variations of ambient temperature so as to cause a control voltage applied to the VCO 31 to be changed, output voltages of the DACs 4, 6 are also changed similarly.
1. A receiver comprising:
a high frequency receiving circuit for which a reception frequency in accordance with a tuning voltage is set;
a local oscillator for generating a local oscillation signal of a frequency in accordance with a control voltage;
a mixing circuit for mixing a signal outputted from said high frequency receiving circuit with said local oscillation signal;
a setting data generating unit for outputting setting data corresponding to a predetermined reception frequency; and
a digital-analog converter for generating said tuning voltage corresponding to the setting data outputted from said setting data generating unit, the tuning voltage being changed with a predetermined temperature coefficient in accordance with ambient temperature,
wherein said digital-analog converter comprises a temperature coefficient setting section constituted by including elements having predetermined temperature coefficients, and
wherein a device constant of said temperature coefficient setting section as a whole is changed in accordance with ambient temperature.
2. The receiver according to claim 1 , wherein said high frequency receiving circuit and said local oscillator, each includes a resonance circuit in which a variable capacitance diode of which electrostatic capacitance can be changed by said control voltage or said tuning voltage, is connected with a coil, and
wherein in each of said resonance circuits, said variable capacitance diode and said coil are connected in a same form.
3. The receiver according to claim 1 , wherein said digital-analog converter changes said tuning voltage in accordance with ambient temperature so as to prevent the reception frequency of said high frequency receiving circuit from fluctuating in accordance with variation of ambient temperature.
4. The receiver according to claim 1 , wherein said digital-analog converter comprises a current source of which current value is set in accordance with a value of said inputted setting data, and said temperature coefficient setting section into which a current generated by the current source flows, and wherein said digital-analog converter outputs a voltage across said temperature coefficient setting section as said tuning voltage.
5. The receiver according to claim 1 , wherein said temperature coefficient setting section includes a plurality of resistances which is formed by a semiconductor manufacturing process and which have temperature coefficients different to each other, and
wherein a connection form of said plurality of resistances is set so that a temperature coefficient of said digital-analog converter becomes a predetermined value.
6. The receiver according to claim 5 , wherein each of said plurality of resistances is formed by a poly-silicon on a semiconductor substrate, and wherein the temperature coefficients are made different by adjusting impurity concentration and carrier types of said poly-silicon.
7. The receiver according to claim 5 , wherein each of said plurality of resistances is formed by utilizing a p-type region or an n-type region on a semiconductor substrate, and wherein the temperature coefficients are made different by adjusting impurity concentration and carrier types of said p-type region or said n-type region.