Low-voltage oscillator with separate startup mode

Claim 2

An integrated circuit oscillator, comprising: first and second leads connectable to a resonator; an amplifier stage having an output side operatively connected to said first lead and an input side operatively connected to said second lead; an output buffer, having an input lead operatively connected to said amplifier stage; a bias feedback path, which provides a quasi-DC signal from said output side of said amplifier back to said input of said output buffer; first and second local power supply leads, at least one of said local power supply leads being connected to a system power supply lead through a resistance which has more than one megohm of resistance; wherein said output buffer comprises a first stage having an NMOS driver transistor a PMOS load transistor and a PMOS pass transistor all operatively connected in series between said first and second local power supply leads, the gates of said driver and load transistors being connected to said input lead of said buffer, wherein said pass transistor has a much lower conductance than said load transistor at equal small-signal gate voltages, and a second stage having an input connected to a node between said driver and load transistors of said first stage; and further comprising an NMOS mode-select transistor and a PMOS mode-select transistor having respective gates connected to an external mode-select signal, said NMOS mode-select transistor being connected between said gate of said pass transistor and system ground, and said PMOS mode-select transistor being connected between said pass transistor and said input lead of said buffer.

Claim 3

An integrated oscillator, comprising: first and second leads connectable to a resonator; an amplifier stage, comprising a PMOS pull-up transistor and an NMOS pull-down transistor, and having an output side operatively connected to said first lead and an input side operatively connected to said second lead; an output buffer, having an input lead operatively connected to receive an AC signal from said input side of said amplifier stage, and connected to receive a quasi-DC signal from said output side of said amplifier stage; a bias feedback path, which provides a quasi-DC signal from said output side of said amplifier back to said input of said output buffer; first and second local power supply leads, at least one of said local power supply leads being connected to a system power supply lead through a resistance which has more than one megohm of resistance; wherein said output buffer comprises a first stage having an NMOS driver transistor, a PMOS load transistor, and a PMOS pass transistor operatively connected in series between said first and second local power supply leads, the gates of said driver and load transistors being connected to said input lead of said buffer, wherein said pass transistor has a channel length which is much longer than that of said pull-up transistor of said amplifier, and a second stage having an input connected to a node between said driver and load transistors of said first stage; and further comprising an NMOS mode-select transistor and a PMOS mode-select transistor having respective gates connected to an external mode-select signal, said NMOS mode-select transistor being connected between said gate of said pass transistor and system ground, and said PMOS mode-select transistor being connected between said pass transistor and said input lead of said buffer.

Claim 4

An integrated oscillator, comprising: first and second leads connectable to a resonator; an amplifier stage, comprising a PMOS pull-up transistor and an NMOS pull-down transistor, and having an output side operatively connected to said first lead and an input side operatively connected to said second lead; an output buffer, having an input lead operatively connected to receive an AC signal from said input side of said amplifier stage, and connected to receive a quasi-DC signal from said output side of said amplifier stage; a bias feedback path, which provides a quasi-DC signal from said output side of said amplifier back to said input of said output buffer; first and second local power supply leads, at least one of said local power supply leads being connected to a system power supply lead through a resistance which has more than one megohm of resistance; wherein said output buffer comprises a first stage having an NMOS driver transistor, a PMOS load transistor, and a PMOS pass transistor operatively connected in series between said first and second local power supply leads, the gates of said driver and load transistors being connected to said input lead of said buffer, wherein said pass transistor has a channel length which is much longer than that of said pull-up transistor of said amplifier, and a second stage having an input connected to a node between said driver and load transistors of said first stage; and further comprising an NMOS mode-select transistor and a PMOS mode-select transistor having respective gates connected to an external mode-select signal, said NMOS mode-select transistor being connected between said gate of said pass transistor and system ground, and said PMOS mode-select transistor being connected between said pass transistor and said input lead of said buffer.

Claim 5

The integrated circuit oscillator of claim 1, wherein said pass transistor has a drawn channel length which is more than twice that of said load transistor.

Claim 6

The integrated circuit oscillator of claim 1, wherein said pass transistor has an effective channel length which is more than 50% greater than that of said load transistor.

Claim 7

The integrated circuit oscillator of claim 1, wherein said pass transistor has an effective channel length which is much greater than that of said load transistor.

Claim 8

The integrated circuit oscillator of claim 1, wherein said resistance consists essentially of a resistor having a resistance value of the order of magnitude of approximately ten megohms.

Claim 9

The integrated circuit oscillator of claim 1, wherein said second local power supply lead is connected through said resistance to ground potential, and said first local power supply lead is connected directly to a positive system power supply voltage.

Claim 10

The integrated circuit oscillator of claim 1, wherein said pass transistor has a greater width and length than said transistor.

Claim 11

The integrated circuit oscillator of claim 1, wherein said amplifier consists essentially of a single CMOS stage.

Claim 12

The integrated circuit oscillator of claim 1, wherein said amplifier stage consists essentially of an NMOS pull-down transistor and a PMOS pull-up transistor connected in series between said first and second local power supply leads.

Claim 13

The integrated circuit oscillator of claim 1, wherein said second stage comprises an NMOS driver transistor and a PMOS load transistor connected in series between said first and second local power supply leads, and wherein said amplifier consists essentially of an NMOS pull-down transistor and a PMOS pull-up transistor connected in series between said first and second local power supply leads, and wherein said pull-down transistor has a channel length which is more than four times as long as the respective channel length of said driver transistor of said second stage of said buffer, and wherein said pull-up transistor has a channel length which is more than four times as long as the respective channel length of said load transistor of said second stage of said buffer.

Claim 14

The oscillator of claim 1, further comprising a quartz crystal connected across said first and second leads.

Claim 15

The oscillator of claim 1, wherein said bias feedback path comprises a transmission gate including NMOS and PMOS transistors.

Claim 16

The integrated circuit oscillator of claim 1, wherein said bias feedback path comprises NMOS and PMOS transistors having long channel lengths.