Semiconductor integrated circuit having oscillator frequency compensation function
It is desired that the temperature dependency of the frequency of a oscillator in a semiconductor IC is compensated in high precision. First signal voltage having temperature dependency and second signal voltage set to be constant independently from the temperature are outputted and A/D converted into first and second converted signals. And the compensation code is generated in response to the ratio between the first and second converted signals. The temperature dependency of the frequency of the oscillator can be compensated by using the compensation code.
1. A semiconductor integrated circuit comprising:
a signal voltage output unit configured to output a first signal voltage having temperature dependency and a second signal voltage being constant independently on a temperature;
an A/D converter configured to convert an input signal voltage into a digital signal based on a reference signal; and
a compensation code generation unit configured to compensate a frequency of an oscillator in response to the digital signal outputted from the A/D converter,
wherein the A/D converter generates a first conversion signal by digitalizing a first difference voltage being a ratio between the first signal voltage and the reference voltage and a second conversion signal by digitalizing a second difference voltage being a ratio between the second signal voltage and the reference voltage, and
the compensation code generation unit generates the compensation code in response to the first conversion signal and the second conversion signal.
2. The semiconductor integrated circuit according to claim 1 , wherein the compensation code generation unit includes:
a comparator configured to receive the first conversion signal and the second conversion signal, and to output a comparison signal indicating a calculated ratio between the first conversion signal and the second conversion signal; and
a compensation value table configured to hold a first defined comparison value indicating the calculated ratio at a first defined temperature and a second defined comparison value indicating the calculated ratio at a second defined temperature different to the first defined temperature, to receive the comparison signal, and to generate the compensation code in response to a temperature characteristic obtained from the first and second defined comparison values and the comparison signal.
3. The semiconductor integrated circuit according to claim 2 , wherein the compensation value table holds a first compensation code corresponding to the first defined comparison value and a second compensation code corresponding to the second defined comparison value, and generates the compensation code at present condition indicated by TTRMnow by using a following equation:
TTRM now={( TRH−TRL )/( TSH−TSL )}*( TS now− TSL )+ TRL
wherein each variable is defined as follows:
TSL: the first defined comparison value;
TSH: the second defined comparison value;
TSnow: a comparison value indicated by the comparison signal;
TRL: the first compensation code; and
TTRMnow: the second compensation code.
4. The semiconductor integrated circuit according to claim 3 , wherein the signal voltage output unit includes:
a band gap reference circuit having a temperature sensor and configured to output a temperature dependent signal corresponding to an output of the temperature sensor and a temperature independent signal set to be constant independently on the output of the temperature sensor;
a first amplifier configured to generate the first signal voltage by amplifying the temperature dependent signal; and
a second amplifier configured to generate the second signal voltage by amplifying the temperature independent signal.
5. The semiconductor integrated circuit according to claim 4 , further comprising:
a switch configured to connect the signal voltage output unit and the A/D converter in a frequency compensation mode, and to cut off the signal voltage output unit and the A/D converter in a normal mode.
6. A frequency compensation code generation method comprising:
(a) generating a first signal voltage having a temperature dependency;
(b) generating a second signal voltage set to be constant against a variation of temperature;
(c) generating a first conversion signal by digitalizing a first difference signal being a ratio of the first signal voltage and a reference voltage;
(d) generating a second conversion signal by digitalizing a second difference signal being a ratio of the second signal voltage and the reference voltage; and
(e) generating a compensation code for compensating a clock frequency of a oscillator in response to a ratio of the first conversion signal and the second conversion signal.
7. The frequency compensation code generation method according to claim 6 , wherein the (e) generating includes:
receiving the first conversion signal and the second conversion signal to output a comparison signal indicating a ratio of the first conversion signal and the second conversion signal; and
referencing a table storing a first defined comparison value indicating the ratio at a first defined temperature and a second defined comparison value indicating the ratio at a second defined temperature being different to the first defined temperature to generate the compensation code corresponding to the comparison signal and a temperature characteristic calculated from the first defined comparison value and the second defined comparison value.
8. The frequency compensation code generation method according to claim 7 , wherein the (e) generating includes:
reading out a first compensation code stored in the table correspondingly to the first defined comparison value and a second compensation code stored in the table correspondingly to the second comparison value from the table; and
generating the compensation code at a present condition indicated by TTRMnow by using a following equation:
TTRM now={( TRH−TRL )/( TSH−TSL )}*( TS now− TSL )+ TRL
wherein each variable is defined as follows:
TSL: the first defined comparison value;
TSH: the second defined comparison value;
TSnow: a comparison value indicated by the comparison signal;
TRL: the first compensation code; and
TTRMnow: the second compensation code.
9. A semiconductor integrated circuit comprising:
an oscillator configured to supply a clock signal;
a frequency compensation circuit having an A/D converter converting an input analog signal into an output digital signal, and configured to compensate a frequency of the clock signal in response to a reference voltage supplied to the A/D converter;
an analog signal supply terminal configured to supply the analog signal; and
a reference voltage supply terminal configured to supply the reference voltage,
wherein the frequency compensation circuit includes:
a signal voltage output unit configured to output a first signal voltage having temperature dependency and a second signal voltage being constant independently on a temperature;
an A/D converter configured to convert an input signal voltage into a digital signal based on a reference signal; and
a compensation code generation unit configured to compensate a frequency of an oscillator in response to the digital signal outputted from the A/D converter, and
the A/D converter generates a first conversion signal by digitalizing a first difference voltage being a ratio between the first signal voltage and the reference voltage and a second conversion signal by digitalizing a second difference voltage being a ratio between the second signal voltage and the reference voltage,
the compensation code generation unit generates the compensation code in response to the first conversion signal and the second conversion signal to supply the compensation code to the oscillator, and
the oscillator compensates a frequency of the clock signal corresponding to the compensation code.