Method and apparatus for switching low voltage CMOS switches in high voltage digital to analog converters

A digital to analog converter (DAC) to receive a range of analog reference voltages and a range of power supply voltages meeting or exceeding a switch breakdown voltage, the DAC to convert a digital input signal having digital input levels into a voltage level of an analog voltage signal within the range of analog reference voltages, the DAC comprising:

• a plurality of digital input terminals to receive the digital input signal having digital input levels, an analog output terminal to output the voltage level of the analog voltage signal, and positive and negative power supply terminals to respectively receive a positive power supply voltage greater than a positive analog reference voltage and a negative power supply voltage less than a negative analog reference voltage;
• a switched R-2R ladder coupled to the analog output terminal and having switches and an R-2R resistance ladder to generate the voltage level of the analog voltage signal responsive to the digital input signal on the analog output terminal, each of the switches having the switch breakdown voltage and a first switch OFF and a first switch ON voltage levels or a second switch OFF and a second switch ON voltage levels, the switched R-2R ladder to receive the positive and negative analog reference voltages and a plurality of switch control signals with each switch control signal coupled to a control terminal of one of the switches;
• a voltage generator coupled to the positive and negative power supply terminals to receive the positive power supply voltage greater than the positive analog reference voltage and the negative power supply voltage less than the negative analog reference voltage, the voltage generator to generate a substantially fixed positive generated OFF voltage greater than the positive analog reference voltage and less than the positive power supply voltage to avoid switch breakdown and provide the first switch OFF voltage level, the voltage generator further to generate a substantially fixed negative generated OFF voltage less than the negative analog reference voltage and more than the negative power supply voltage to avoid switch breakdown and provide the second switch OFF voltage level;
• and
• a switch controller coupled to the plurality of digital input terminals and the voltage generator to receive the digital input signal having digital input levels and the substantially fixed positive and negative generated OFF voltages and further coupled to each control terminal of each switch of the switched R-2R ladder to generate the plurality of switch control signals thereon, the switch controller to form a negative ON voltage responsive to the negative analog reference voltage to avoid switch breakdown and to provide the second switch ON voltage level, the switch controller further to form a positive ON voltage responsive to the positive analog reference voltage to avoid switch breakdown and to provide the first switch ON voltage level, the switch controller to generate the plurality of switch control signals having first and second switch ON and OFF voltage levels responsive to the digital input signal, the positive and negative generated OFF voltages, and the positive and negative analog reference voltages, and wherein, switch breakdown is avoided and the first and second switch OFF voltage levels and first and second switch ON voltage levels are coupled to the plurality of switch control signals.

A method for switching switches in a digital to analog converter having a switch breakdown voltage less than or equal to a power supply voltage range to convert a digital input signal having digital input signal levels into an analog output signal, the method comprising:

• a) providing a switched R-2R ladder having switches to generate the analog output signal in response to the digital input signal, each switch having a switch control terminal and the switch breakdown voltage;
• b) receiving a positive power supply and a negative power supply having the power supply voltage range greater than or equal to the switch breakdown voltage;
• c) receiving a positive analog reference voltage and a negative analog reference voltage, the range between the positive analog reference voltage and the negative analog reference voltage being less than the switch breakdown voltage;
• d) generating a positive substantially fixed generated OFF voltage greater than the positive analog reference voltage and a negative substantially fixed generated OFF voltage less than the negative analog reference voltage, the range of voltage between the positive generated OFF voltage and the negative generated OFF voltage being less than the switch breakdown voltage;
• e) forming a positive ON voltage and a negative ON voltage respectively in response to the positive analog reference voltage and the negative analog reference voltage, the positive ON voltage being less positive than the positive analog reference voltage by a predetermined voltage level and the negative ON voltage being more positive than the negative analog reference voltage by a variable voltage level;
• f) receiving the digital input signal having digital input signal levels and shifting the voltage levels of the digital input signal into the positive and negative generated OFF voltage levels for a high logic level input or a low logic level input to generate a shifted digital input signal;
• and
• g) coupling the positive or negative generated OFF voltage to switch control terminals and the positive or negative ON voltage to switch control terminals to switch switches in a digital to analog converter and to avoid switch breakdown.

A method for providing a range of an analog output signal in a digital to analog converter exceeding a switch breakdown voltage, the digital to analog converter to convert a digital input signal having digital input signal levels into the analog output signal, the method comprising:

• a) providing a switched R-2R ladder having switches to generate an intermediate analog output signal in response to the digital input signal, each switch having a switch control terminal and the switch breakdown voltage;
• b) providing an amplifier coupled to the switched R-2R ladder, the amplifier having a gain greater than one;
• c) the switched R-2R ladder generating the intermediate analog output signal in response to the digital input signal;
• and
• d) the amplifier amplifying the intermediate analog output signal using the gain greater than one into the analog output signal having the range exceeding the switch breakdown voltage of the switches in the switched R-2R ladder.

A method for providing a range of an analog output signal in a digital to analog converter exceeding a switch breakdown voltage, the digital to analog converter to convert a digital input signal having digital input signal levels into the analog output signal, the method comprising:

• a) providing a switched R-2R ladder having switches to generate an intermediate analog output signal in response to the digital input signal, each switch having a switch control terminal and the switch breakdown voltage;
• b) providing an amplifier coupled to the switched R-2R ladder, the amplifier having a gain greater than one;
• c) the switched R-2R ladder generating the intermediate analog output signal in response to the digital input signal and the amplifier receiving the intermediate analog output signal and amplifying it with a gain greater than one into the analog output signal having the range exceeding the switch breakdown voltage;
• and
• d) providing a switch controller to control the switches in the switched R-2R ladder;
• the switch controller,
• i) receiving a positive analog reference voltage and a negative analog reference voltage, the range between the positive analog reference voltage and the negative analog reference voltage being less than the switch breakdown voltage;
• ii) generating a positive substantially fixed generated OFF voltage greater than the positive analog reference voltage and a negative substantially fixed generated OFF voltage less than the negative analog reference voltage, the range of voltage between the positive generated OFF voltage and the negative generated OFF voltage being less than the switch breakdown voltage;
• iii) forming a positive ON voltage and a negative ON voltage respectively in response to the positive analog reference voltage and the negative analog reference voltage, the positive ON voltage being less positive than the positive analog reference voltage by a predetermined voltage level and the negative ON voltage being more positive than the negative analog reference voltage by a variable voltage level;
• iv) receiving the digital input signal having digital input signal levels and shifting the voltage levels of the digital input signal into the positive and negative generated OFF voltage levels for a high logic level input or a low logic level input to generate a shifted digital input signal;
• and
• v) coupling the positive or negative generated OFF voltage to switch control terminals and the positive or negative ON voltage to switch control terminals for switching switches in a digital to analog converter and avoiding the switch breakdown voltage.

A method for converting a digital input signal having digital input signal levels into an analog output signal having a voltage range exceeding a switch breakdown voltage, the method comprising:

• level shifting high voltage power supply levels exceeding the switch breakdown voltage to safe control voltage levels not exceeding the switch breakdown voltage;
• switching switches in a switched R-2R ladder using the safe control voltage levels to generate an intermediate analog output signal in response to the digital input signal, the switches in the switched R-2R ladder having the switch breakdown voltage;
• and
• amplifying the intermediate analog output signal by a gain greater than one to generate the analog output signal having the voltage range exceeding the switch breakdown voltage of the switches in the switched R-2R ladder.