Telecommunications – Transmitter and receiver at same station – With transmitter-receiver switching or interaction prevention
Reexamination Certificate
1996-11-20
2003-01-21
Appiah, Charles N. (Department: 2682)
Telecommunications
Transmitter and receiver at same station
With transmitter-receiver switching or interaction prevention
C455S073000, C455S084000
Reexamination Certificate
active
06510309
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an amplifying circuit for high frequency and base-band applications. More particularly, the present invention relates to a radio frequency (RF) or microwave frequency amplification circuit for use in a receive mode and in a transmit mode.
BACKGROUND OF THE INVENTION
Various wireless communication systems, such as, cellular telephones, cordless telephones, wireless modems, radios, and personal handy phone systems (PHS), require intermediate frequency (IF) amplifiers which amplify or attenuate receive IF signals (.e.g., in the receive mode) and transmit IF signals (e.g., in the transmit mode). The intermediate frequency is a frequency to which a signal wave is shifted as an intermediate step in transmission or reception. The intermediate frequency can be any frequency; in radio frequency applications, the intermediate frequency is often between 1 MHz and 1 GHz.
Generally, the IF signals are amplified or attenuated by semiconductor or integrated circuit devices. In most high frequency amplification schemes, the receive IF signal and the transmit IF signal are provided through a discrete or off-chip filter to remove spacious signals outside of a band width centered at the intermediate frequency. The discrete filter is generally a physically large device which cannot be integrated on a semiconductor substrate.
With reference to
FIG. 1
, a communication system
10
includes a conventional IF amplifier circuit
9
integrated on a semiconductor substrate
11
. Circuit
9
includes a receive path amplifier
20
, a transmit path amplifier
22
, a receive path amplifier
24
, a transmit path amplifier
26
, a switch circuit
28
, and a switch circuit
30
. Switch circuit
28
includes a terminal
44
, a terminal
46
, and a common terminal
54
. Switch circuit
30
includes a common terminal
56
, a terminal
48
, and a terminal
52
.
Amplifier
20
has an input coupled to a receive path input
12
and an output coupled to terminal
44
of switch circuit
28
. Amplifier
22
has an input coupled to terminal
46
of switch circuit
28
and an output coupled to transmit path output
18
. Amplifier
26
has an input coupled to transmit path input
16
and an output coupled to terminal
52
of switch circuit
30
. Amplifier
24
has an input coupled to terminal
28
of switch circuit
30
and an output coupled to receive path output
14
.
An off-chip filter
38
is coupled between amplifiers
20
and
24
and between amplifiers
22
and
26
(e.g., between switch circuits
28
and
30
). Filter
38
has a terminal
40
coupled to common terminal
54
of switch circuit
28
and a terminal
42
coupled to common terminal
56
of switch circuit
30
.
In a receive mode of operation, receive IF signals are provided on receive path input
12
and amplified by amplifier
20
. The amplified IF signal is provided through switch circuit
28
, filter
38
, and switch circuit
30
to amplifier
24
. Amplifier
24
reamplifies the IF signal and provides the signal to receive path output
14
. Receive path input
12
and receive path output
14
can be terminals, pins, or off-chip connections for substrate
11
, or they can be internal connections to other circuit components on substrate
11
.
In a transmit mode of operation, transmit IF signals are provided on transmit path input
16
and amplified by amplifier
26
. The amplified IF signal is provided through switch circuit
30
, filter
38
, and switch circuit
28
to amplifier
22
. Amplifier
22
reamplifies the IF signal and provides the transmit IF signal to transmit path output
18
. Transmit path input
16
and transmit path output
18
can be terminals, pins, or off-chip connections for substrate
11
, or they can be internal connections to other components on substrate
11
.
Amplifier circuit
9
associated with system
10
and semiconductor substrate
11
is disadvantageous for various reasons. First, amplifier circuit
9
requires identical input/output (I/O) impedances for amplifiers
20
,
22
,
24
, and
26
. For example, the output impedance of amplifier
20
must match the input impedance for amplifier
22
as well as for filter
38
. Similarly, the input impedance for amplifier
24
must match the output impedance for amplifier
26
as well as for filter
38
. Matching amplifier I/O impedances is difficult and adds to the complexity of designing amplifier circuit
9
on substrate
11
, especially in light of differing temperature characteristics and process variations associated with amplifiers
20
,
22
,
24
, and
26
. Second, amplifier circuit
9
requires that off-chip filter
38
be bidirectional. In the receive mode, the IF signal travels from terminal
40
to terminal
42
. In the transmit mode, the IF signal travels from terminal
42
to terminal
40
. Bidirectional filters are more expensive and rarely have exactly the same response characteristics in both directions. This scheme precludes the use of active filters. Third, the scheme for amplifier circuit
9
on substrate
11
requires that switch circuits
28
and
30
be bidirectional or passive. Bidirectional switches for high frequency circuits cannot easily be designed in bipolar silicon substrate integrated circuit devices. Switches must be carefully designed so as not to degrade impedances which may lead to excessively large or complicated circuitry.
Thus, there is a need for an IF amplifier circuit which can utilize unidirectional switches and unidirectional filters. Further, there is a need for an IF amplifier circuit which utilizes two amplifiers for both the receive mode and the transmit mode of operation. Further still, there is a need for an amplifier scheme where IF amplifier outputs do not have to be matched to IF amplifier inputs as well as to the off-chip filter.
SUMMARY OF THE INVENTION
The present invention relates to a high frequency amplification circuit integrated on a single substrate for use with an off-chip filter. The amplification circuit operates in a receive mode and in a transmit mode. The amplification circuit includes a first switch, a first amplifier, a second amplifier, and a second switch. The first switch has a receive input, a transmit input, and a common output. The first amplifier has a first input and a first output. The first input is coupled to the common output of the first switch. The first output is coupleable to the off-chip filter. The second amplifier has a second input coupleable to the off-chip filter and a second output. The second switch has a common input, a transmit output, and a receive output. The common input is coupled to the second output.
The present invention is further related to an intermediate frequency amplifier circuit for use in a receive mode and in a transmit mode. The intermediate frequency amplifier circuit includes a first intermediate frequency switch circuit, a first amplifier circuit, a second amplifier, and a second intermediate frequency switch circuit. The first intermediate frequency switch circuit has a receive input, a transmit input, and a first switch output. The first amplifier circuit has a first amplifier input and a first amplifier output. The first amplifier input is coupled to the first switch output. The second amplifier has a second amplifier input and a second amplifier output. The second amplifier input is in communication with the first amplifier output. The second intermediate frequency switch circuit has a second switch input, a transmit output, and a receive output. The second switch input is coupled to the second amplifier output. The intermediate frequency amplifier circuit has a unidirectional signal path through the first and second amplifiers for both the receive mode and the transmit mode.
The present invention still further relates to an intermediate frequency amplifier having a receive mode and a transmit mode. The intermediate frequency amplifier includes a first intermediate frequency switch means for coupling a receive input to a first switch output in the receive mode and for coupling a transmit input t
Andrys Paul R.
Lawrence Ed F.
Thompson Philip H.
Appiah Charles N.
Conexant Systems Inc.
Foley & Lardner
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