Direct conversion receiver

Details Direct conversion receiver Direct conversion receiver

1999-03-02

2002-03-19

Trost, William (Department: 2683)

Telecommunications

Receiver or analog modulated signal frequency converter

Local control of receiver operation

C455S147000, C331S002000

Reexamination Certificate

active

06360087

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to direct conversion receivers, and more specifically, to direct conversion receivers employing a mixer configured to reduce the effects of leakage between the radio frequency and local oscillator input ports thereof.
2. Background
A radio receiver of the type currently employed in mobile wireless phones is illustrated in FIG.
1
. As shown, the receiver comprises a first mixer
1
, having a radio frequency (RF) input port
5
coupled to an antenna
11
, and a local oscillator (LO) input port
8
. The mixer has an output port
12
coupled, through signal line
6
, to the input of a band-pass filter (BPF)
3
. The BPF
3
has an output coupled to the intermediate frequency (IF) input port
10
of a second mixer
2
. The second mixer
2
also has a local oscillator (LO) input port
9
. The output port
14
of mixer
2
is coupled, through signal line
15
, to the input of low-pass filter (LPF)
4
. The output of LPF
4
is coupled to signal line
7
.
First mixer
1
is configured to multiply the signals received at the RF and LO input ports thereof, and provide the multiplied signal at the output port thereof. The frequency of the signal received at the RF input port is f
RF
, and the frequency of the signal received at the LO input port is f
LO1
. The signal received at the RF input port is derived from a signal received over antenna
11
. Typically, this signal represents a digitized audio signal which has been modulated onto an RF carrier signal. In the following discussion, this digitized audio signal will be referred to as the baseband signal, but it should be appreciated that, in practice, the baseband signal can be a desired signal other than a digitized audio signal, including a data signal.
The signal provided at the output port
12
will have first order components at frequencies f
RF
−f
LO1
and f
RF
+f
LO1
. The frequency f
RF
−f
LO1
is an intermediate frequency which will be referred to as f
IF
. In one implementation, f
RF
is 900 MHz, f
LO1
is 450 MHz, and f
IF
is 450 MHz. In this implementation, the first order components of the output signal will be at 1350 MHz and 450 MHz.
BPF
3
has a passband centered at f
IF
, and is configured to allow passage of the IF component of the output signal, and to prevent passage of the other first order component, that is, the component at the frequency f
RF
+f
LO1
. BPF
3
also rejects any unwanted signals outside the desired band around f
RF
−f
LO1
. This IF component is then provided as an input to input port
10
of mixer
2
.
The signal provided as an input to the LO port of mixer
2
has a frequency f
LO2
. This frequency is selected so that it is the same as the frequency f
IF
of the signal provided at the input port
10
. Mixer
2
multiplies these two signals, and provides the multiplied signal on output port
14
. The output signal will have two first order components, one at the baseband frequency, f
BB
, and the other at twice the intermediate frequency f
IF
.
The output signal from mixer
2
is provided as an input to LPF
4
. LPF
4
is configured to allow passage of the baseband component of the signal output from mixer
2
, and prevent passage of the high frequency component, that is, the frequency at twice f
IF
, of the output of mixer
2
. The baseband component is thus provided as an output of the receiver line
7
.
In operation, the receiver of
FIG. 1
functions as follows. A signal is received over antenna
11
representing a baseband signal modulated onto an RF carrier signal. The signal is passed through mixer
1
, which produces at its output port a signal having a first order component representative of the baseband signal, but at an intermediate frequency rather than baseband frequencies, and also a second first order component. The signal is passed through BPF
2
to isolate the intermediate frequency component from the other first order component. This intermediate frequency component is then passed through mixer
2
, which produces at its output port a signal having a baseband component and an intermediate frequency component. The signal is then passed through LPF
4
to isolate the baseband component from the higher frequency component. LPF
4
thus produces at its output a signal representative of the baseband signal.
As is apparent from the foregoing description, the operation of the receiver of
FIG. 1
proceeds in two basic steps. In the first step, the baseband portion of the incoming RF signal is down converted to an intermediate frequency. In the second step, the baseband portion at the intermediate frequency is down converted to the baseband frequency. Each of these steps is performed on and through distinct elements, the first step, through mixer
1
and BPF
3
, and the second step, through mixer
2
and LPF
4
.
Because of the cost and complexity of downconverting the baseband portion in multiple steps in the receiver of
FIG. 1
, and the cost of the elements needed to perform these multiple steps, the receiver of
FIG. 1
is not ideal.
Accordingly, an object of the subject invention is a receiver which overcomes the disadvantages of the prior art. Additional objects and advantages will be apparent to those of skill in the art who practice the invention or will be set forth in the disclosure which follows.
3. Related Application
This application is relation to a co-pending patent application entitled “PREPROCESSOR AND RELATED FREQUENCY TRANSLATOR,” Lyon & Lyon Dkt. No. 240/111, Serial No. To Be Assigned, which is owned in common by the assignee hereof, and is being filed on even date herewith. This application is hereby fully incorporated by reference herein as though set forth in full.


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patent: 6018553 (2000-01-01), Sanielevici et al.
patent: 6029052 (2000-02-01), Isberg et al.
patent: 6040738 (2000-03-01), Uchida
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patent: 0 798 880 (1997-10-01), None
patent: 92 01337 (1992-01-01), None
Ian Doyle, “A Simplified Subharmonic I/Q Modulator”,Applied Microwave&Wireless,Oct. 1998.
Takafumi Yamaji et al., “An I/Q Active Balanced harmonic Mixer with IM2 Cancelers and a 45° Phase Shifter”,IEEE Journal of Solid-State Circuits,vol. 33, No. 12, Dec. 1998.

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