OTA based fast lock PLL
View Patent ↗A charge pump, comprising a charge pump output may be operatively coupled to a filter input of a loop filter. A first amplifier input of an operational transconductance amplifier (OTA) may be operatively coupled to the filter input and the charge pump output, and the second amplifier input is operatively coupled to the amplifier output and filter output.
1. An apparatus comprising:
a charge pump, comprising a charge pump output;
a loop filter, comprising a filter input and a filter output, wherein the charge pump output is operatively coupled to the filter input, and wherein the loop filter comprises:
a filter resistor;
a filter capacitor coupled in series with the filter resistor; and
a pole capacitor coupled in parallel with the filter resistor and the filter capacitor; and
an operational transconductance amplifier (OTA), comprising a first amplifier input, a second amplifier input, and an amplifier output, wherein the first amplifier input is operatively coupled to the filter input and the charge pump output, and the second amplifier input is operatively coupled to the amplifier output and the filter output.
2. The apparatus of claim 1 , further comprising:
an offset resistor, having a first offset node and a second offset node, wherein the first offset node is operatively coupled to the amplifier output and the second offset node is operatively coupled to the second amplifier input and the filter output.
3. The apparatus of claim 1 , wherein the OTA is a rail-to-rail input OTA.
4. The apparatus of claim 1 , wherein the OTA is folded cascoded amplifier.
5. The apparatus of claim 1 , wherein the charge pump, the loop filter, and the OTA are components of a phase-locked loop (PLL).
6. The apparatus of claim 1 , further comprising:
a phase-frequency detector (PFD), comprising a reference input and a feedback input operatively coupled to the charge pump.
7. The apparatus of claim 6 , further comprising:
a voltage controlled oscillator (VCO), comprising an oscillator input and an oscillator output, wherein the oscillator input is operatively coupled to the first amplifier input, the filter input, and the charge pump output, and the oscillator output is operatively coupled to the feedback input of the PFD.
8. The apparatus of claim 7 , further comprising:
an N-divider circuit, comprising an N-divider input and an N-divider output, wherein the N-divider input is operatively coupled to the oscillator output of the VCO and the N-divider output is operatively coupled to the feedback input of the PFD.
9. A device comprising:
a phase-locked loop (PLL) comprising;
a charge pump, comprising a charge pump output;
a loop filter, comprising a filter input and a filter output, wherein the charge pump output is operatively coupled with the filter input, and wherein the loop filter comprises:
a filter resistor;
a filter capacitor coupled in series with the filter resistor; and
a pole capacitor coupled in parallel with the filter resistor and the filter capacitor; and
an operational transconductance amplifier (OTA), comprising a first amplifier input, a second amplifier input, and an amplifier output, wherein the first amplifier input is operatively coupled to the filter input and the charge pump output, and the second amplifier input is operatively coupled to the amplifier output and filter output; and
a data I/O bus, operatively coupled to the PLL.
10. The device of claim 9 , further comprising:
an offset resistor, operatively coupled to the OTA, to reduce an offset of the OTA.