Selective call radio having an integrated frequency...

Details Selective call radio having an integrated frequency... Selective call radio having an integrated frequency...

1998-12-04

2002-04-09

Cumming, William (Department: 2684)

Telecommunications

Receiver or analog modulated signal frequency converter

C327S113000, C708S300000

Reexamination Certificate

active

06370365

ABSTRACT:

FIELD OF THE INVENTION
This invention relates in general to selective call radios, and particularly, to a selective call radio having an integrated frequency conversion circuit.
BACKGROUND OF THE INVENTION
Consumer demand for smaller wireless products such as pagers and cellular phones continues to drive manufacturers to miniaturize circuit blocks in SCRs (selective call radios).
FIG. 1
illustrates a classical structure of a prior art dual conversion radio receiver
100
. This structure is commonly utilized in wireless communication products.
As shown, the dual conversion receiver
100
consists of an antenna
102
coupled in series with a low-noise amplifier
104
and a preselector filter
106
. The preselector filter
106
is essentially a bandpass filter for attenuating undesired signals that are far from a desired signal in the frequency spectrum. This filtered signal is down-converted by a first mixer
108
, which is coupled to an injection frequency signal from a first LO (local oscillator)
110
. Once the filtered radio signal has been down-converted to an IF (intermediate frequency) signal, the IF signal is again filtered by a selectivity filter
112
to substantially attenuate undesired signals close in frequency to the desired signal. The filtered signal generated by the selectivity filter
112
is then down-converted by a second mixer
114
coupled to a second LO
116
, which generates a baseband signal
118
.
Presently, a large portion of the circuits of the first mixer
108
and the first local oscillator
110
are constructed with discrete electrical components, rather than integrated into one or more IC (integrated circuit) components. Similar to the first LO
110
, the manufacture of the second mixer
114
and the second LO
116
also consists of discrete circuit components for generating the second injection frequency. Thus, neither the first nor the second stage of frequency conversion circuits have been fully integrated into an IC in prior art systems. Historically, designers of portable radio units have avoided the integration of the foregoing circuits, especially in narrow-band applications, due to the high side band noise resulting from the integration of local oscillators, which in turn limits the ACIPR (Adjacent Channel Interference Protection Ratio) of the receiver.
In view of a desire for miniaturizing wireless products in the consumer market, a need exists in selective call radios for integrating a frequency conversion circuit into an IC, thereby overcoming the disadvantages described in the prior art.


REFERENCES:
patent: 4893316 (1990-01-01), Janc et al.
patent: 5140198 (1992-08-01), Atherly et al.
Yang, Lee & Co, A Low Jitter 0.3-165 Mhz CMOS PLL Frequency Synthesizer for 3 V/5 V Operation, IEEE Jornal of Solid State Circuits, vol. 32, No. 4, Apr. 1997, pp. 585-586.

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