Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2002-12-12
2004-10-19
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S157000
Reexamination Certificate
active
06806759
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to charge pumps and more specifically to an external tri-state charge pump for extending the steering line output range of a charge pump that is internal to a synthesizer integrated circuit.
BACKGROUND OF THE INVENTION
Synthesizer integrated circuits (“ICs”) are used in a number of different devices. These include two-way radios, wireless personal communication devices, wireless automotive devices, and home and entertainment devices requiring a stable radio frequency to transmit or receive audio, video, and data signals. Some prior art synthesizer ICs have phase detector (or dual) outputs that are used to control existing external charge pump designs for use in applications that require a range of control voltage values. As die shrinks and new processes are developed to reduce IC manufacturing costs, synthesizer IC's with phase detector outputs are being phased out to reduce pin count and package size. The synthesizer ICs with phase detector outputs are being replaced by synthesizer ICs with internal charge pumps. However, current synthesizer ICs with an internal charge pump have a reduced maximum voltage, which may be insufficient for many applications such as high tier base stations, mobile, and portable two-way radios.
FIG. 1
illustrates a simple block diagram of a typical phase locked loop (“PLL”) circuit
100
, such as may be used in wide range of transmitting and receiving devices described above. PLL circuit
100
comprises a synthesizer IC
110
with an internal charge pump (not shown). Synthesizer IC
110
has a prescaler input
112
and a single pin output
114
that is a steering line output from the internal charge pump. The output signal at output
114
is typically a minimum voltage value, a maximum voltage value or a tri-state output. PLL circuit
100
further comprises an external charge pump circuit
120
, having an input
122
coupled to synthesizer output
114
, and having an output
124
. External charge pump circuit
120
may be, for instance, a prior art external charge pump design or a charge pump circuit in accordance with the present invention. PLL circuit
100
also includes a loop filter
130
coupled to the charge pump output
124
. Depending upon the application and circuit arrangement, loop filter
130
may include circuit components such as one or more resistors, and one or more capacitors depending on the order of the filter. In addition, although loop filter
130
is illustrated as being external to charge pump
120
, those of ordinary skill in the art will realize that the loop filter may be integrated into the charge pump. Finally, PLL circuit
100
includes a voltage-controlled oscillator (“VCO”)
140
coupled between the loop filter
130
and synthesizer input
112
via a VCO feedback circuit
160
, and also includes a PLL output
150
.
FIG. 2
is a circuit diagram illustrating a PLL circuit
200
having a prior art charge pump circuit. PLL circuit
200
comprises a typical synthesizer IC
210
with an input
212
and an output
214
. Synthesizer IC
210
includes an internal charge pump (not shown) that generates a maximum steering line voltage at output
214
that is insufficient for many applications, as noted above. PLL circuit
200
further comprises a prior art external charge pump for extending the steering line range at output
214
. This external charge pump includes an operational amplifier (“op-amp”)
220
, resistors
222
and
224
and a loop filter
230
, which includes a resistor
238
and capacitors
232
,
234
and
236
. The charge pump functions in a voltage mode using op-amp
220
as a voltage-to-voltage converter to generate the increased steering line range. Finally, PLL circuit
200
includes a VCO
240
coupled between op-amp
220
and synthesizer input
212
via a VCO feedback circuit
260
, and also includes a PLL output
250
.
A shortcoming of the above prior art charge pump is that it requires an op-amp, which is inherently noisy and raises the cost of the device. Another shortcoming of the prior art charge pump design is that although this design is acceptable at room temperatures, it fails over environmental extremes, e.g., humidity, temperature, etc. Still another shortcoming of the prior art charge pump design is that it operates in only two states, and does not address the tri-state output of the synthesizer IC.
Thus, there exists a need for an external charge pump that extends the upper limit of a synthesizer IC's internal charge pump steering line range, that operates over environmental extremes, and that operates to address the tri-state output of the synthesizer IC.
REFERENCES:
patent: 5619161 (1997-04-01), Novof et al.
patent: 5638029 (1997-06-01), O'Shaughnessy
patent: 6384638 (2002-05-01), Nayebi et al.
patent: 6611160 (2003-08-01), Lee et al.
Callahan Timothy P.
Cox Cassandra
Davis Valerie M.
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