GB2261346A - Transmitter/receiver output/input stages - Google Patents

Abstract

A transmitter/receiver output/input stage comprises first (21) and second (23) mixers and first (25) and second (27) oscillators the second (27) of which is a variable frequency oscillator. As a receiver input stage the first mixer (21) mixes a received signal with a signal generated by the first oscillator (25) to provide a first signal to the second mixer (23). The second mixer (23) mixes the first signal with a signal generated by the second oscillator (27) to provide an output signal of a predetermined frequency. As a transmitter output stage the second oscillator (27) is retuned to the frequency of the first signal to provide to the first mixer (21) a second signal, the first mixer (21) mixing the second signal with the signal generated by the first oscillator (25) to provide an output signal at the frequency of the received signal. <IMAGE>

Description

Transmitter/Receiver Output/Input Stages This invention relates to transmitter/receiver output/input stages, that is to circuitry which in one mode of operation functions as an output stage of a transmitter and which in another mode of operation functions as an input stage of a receiver.

One known transmitter/receiver output/input stage is shown in Figure 1 of the accompanying drawings and is for use over a range of transmit and receive frequencies. It comprises a first section 2, a second section 4, a fixed frequency oscillator 9, and a switch 15. The first section 2 comprises a mixer 1, a variable frequency oscillator 5, and a bandpass filter 11. The second section 4 comprises a mixer 3, a fixed frequency oscillator 7, and a bandpass filter 13.

In use as a receiver input stage switch 15 is switched as shown in dotted in Figure 1 to switch out of circuit oscillator 9, and a modulated radio frequency (rf) signal of a frequency f1 within the transmit/receive range is received by mixer 1. Oscillator 5 is tuned to a frequency f051 which when mixed in mixer 1 with frequency f1 produces a signal which includes a component at a first predetermined so called first intermediate frequency fIF1. Bandpass filter 11 filters out components of the signal produced by mixer 1 other than the component at the first intermediate frequency fIF1.

The output of filter 11 is mixed in mixer 3 with a frequency f052 generated by oscillator 7, which frequency f052 when mixed with the first intermediate frequency fIF1 produces a signal including a component at a second predetermined so called second intermediate frequency fIF2. Bandpass filter 13 filters out components of the signal produced by mixer 3 other than the component at the second intermediate frequency fIF2e The output of filter 13 leaves the receiver input stage by way of switch 15 for subsequent demodulation.

The purpose of the first section 2 is to upconvert any received frequency, for example frequency f1, within the transmit/receive range to the same intermediate frequency fix19 which frequency fIF1 is greater than the highest frequency in the transmit/receive range. The frequency range of variable frequency oscillator 5 is such that oscillator 5 can generate the frequency required to be mixed with any frequency within the transmit/receive range to provide intermediate frequency fIF1. The upconversion ensures that for a given frequency setting of oscillator 5 there is only one frequency within the transmit/receive range which will give rise to the first intermediate frequency fIF1 and hence the second intermediate frequency fIF2.

The purpose of the second section 4 is to downconvert intermediate frequency fIF1 (to frequency fIF2).

In use as a transmitter output stage for the transmission of a modulated r.f. signal of the same frequency f1 as the modulated r.f. signal received in use as a receiver input stage, oscillator 9 is switched into circuit by switching switch 15 as shown in solid in Figure 1. Modulation is applied to the signal generated by oscillator 9. Thenceforth the process for the aforesaid transmission is the reverse of the aforedescribed process of reception.

The intermediate frequency fIF2 of oscillator 9 is applied by way of switch 15 and bandpass filter 13 to mixer 3 where it is mixed with frequency f052 from oscillator 7. The output of mixer 3 passes by way of filter 11 to mixer 1 where the output of filter 11 of frequency fIF1 is mixed with frequency f051 from oscillator 5 thereby to provide at the output of mixer 1 a modulated r.f. signal of frequency f1, the frequency of the modulated r.f. signal received in use as a receiver input stage.

In the use as a transmitter output stage the second section 4 upconverts frequency fIF2 to frequency fIF1 and the first section 2 downconverts frequency fIF1 to the frequency, for example frequency f1, within the transmit/receive range required to be transmitted.

The known transmitter/receiver output/input stage of Figure 1 may include one or more further sections between filter 13 and switch 15, each further section comprising a mixer, oscillator, and filter, as section 4. In use as a receiver input stage each further section provides downconversion to a further intermediate frequency.

In use as a transmitter output stage, oscillator 9 is tuned to a frequency equal to the intermediate frequency output by the last mixer/oscillator/filter section in use as a receiver input stage.

It is an object of the present invention to simplify the aforedescribed known transmitter/receiver output/input stages thereby to reduce their cost.

According to the present invention there is provided a transmitter/receiver output/input stage comprising first and second mixers and first and second oscillators the second of which is a variable frequency oscillator, as a receiver input stage said first mixer mixing a signal received thereby with a signal generated by said first oscillator thereby to provide a first signal to said second mixer, said second mixer mixing said first signal with a signal generated by said second oscillator to provide an output signal of the receiver input stage of a predetermined frequency, as a transmitter output stage said second oscillator being retuned to the frequency of said first signal thereby to provide to said first mixer a second signal, said first mixer mixing said second signal with said signal generated by said first oscillator to provide an output signal of the transmitter output stage of the frequency of said signal received by said first mixer in the use as a receiver input stage.

Preferably: said first oscillator is a variable frequency oscillator such that said output/input stage is usable over a range of transmit and receive frequencies; the mixing by said first mixer in the use as a receiver input stage upconverts the frequency in said range received by the first mixer to a frequency greater than the highest frequency in said range; and the mixing by said second mixer in the use as a receiver input stage downconverts the frequency of said first signal.

A transmitter/receiver output/input stage in accordance with the present invention will now be described, by way of example, with reference to Figures 2, 3 and 4 of the accompanying drawings, Figure 2 of which is a schematic circuit diagram of the output/input stage, Figures 3 and 4 of which illustrate modifications to the output/input stage of Figure 1.

Referring to Figure 2, the output/input stage is for use over the range of transmit and receive frequencies 0-1 GHz. It comprises a first section 20 and a second section 22. The first section 20 comprises a 1.36 - 2.36 GHz variable frequency oscillator 25, a mixer 21, and a bandpass filter 29 tuned to 1.36 GHz. The second section 22 comprises a variable frequency oscillator 27 capable of generating 1.28 GHz and 1.36 GHz, a mixer 23, and a bandpass filter 31 tuned to 0.08 GHz.

In use as a receiver input stage a modulated r.f. signal of a frequency f2 within the transmit/receive range 0-1 GHz is received by mixer 21. Oscillator 25 is tuned to a frequency fVFO1 within the range 1.36 - 2.36 0Hz which when mixed in mixer 21 with frequency f2 produces a signal which includes a component at a first intermediate frequency of 1.36 GHz. Bandpass filter 29 filters out components of the signal produced by mixer 21 other than the component at frequency 1.36 GHz.

The output of filter 29 is mixed in mixer 23 with a frequency of 1.28 0Hz generated by oscillator 27 to produce a signal including a component at a second intermediate frequency of 0.08 GHz. Bandpass filter 31 filters out components of the signal produced by mixer 23 other than the component at frequency 0.08 GHz.

The output of filter 31 leaves the receiver input stage for subsequent demodulation.

The purpose of the first section 20 is to upconvert any received frequency, for example frequency fe, in the range 0-1 0Hz to the same intermediate frequency of 1.36 GHz, which frequency of 1.36 0Hz is greater than the highest frequency of 1 0Hz in the 0-1 0Hz range. Since the frequency range of oscillator 25 is 1.36 2.36 GHz, oscillator 25 can generate the frequency required to be mixed with any received frequency in the range 0-1 0Hz to provide the first intermediate frequency of 1.36 GHz.The upconversion ensures that for a given frequency setting of oscillator 25 there is only one frequency within the 0-1 0Hz range which will give rise to the first intermediate frequency of 1.36 0Hz and hence the second intermediate frequency of 0.08 GHz. It does this because it ensures that the unwanted so called image responses are received at frequencies equal to the frequency of oscillator 25 plus the first intermediate frequency of 1.36 GHz, which frequencies will always be above the transmit/receive range of 0-1 GHz. The wanted responses are received at frequencies equal to the frequency of oscillator 25 minus the first intermediate frequency of 1.36 GHz, which frequencies cover the transmit/receive range of 0-1 GHz.

The purpose of the second section 22 is to downconvert the first intermediate frequency of 1.36 0Hz to the second intermediate frequency of 0.08 GHz.

Thus, it can be seen that the output/input stage of Figure 2 in use as a receiver input stage functions in the same way as the known output/input stage of Figure 1.

In use as a transmitter output stage for the transmission of a modulated r.f. signal of the same frequency f2 as the modulated r.f. signal received in use as a receiver input stage, oscillator 27 of the output/input stage of Figure 2 is retuned to the first intermediate frequency of 1.36 GHz. Modulation is applied to the signal generated by oscillator 27.

The intermediate frequency of 1.36 0Hz generated by oscillator 27 appears at the output of mixer 23, and passes by way of filter 29 to mixer 21 where it is mixed with frequency fVFO1 from oscillator 25 to produce at the output of mixer 21 a modulated r.f.

signal of frequency f2, the frequency of the modulated r.f. signal received in use as a receiver input stage.

In the use as a transmitter output stage oscillator 27 of the second section 22 generates a frequency of 1.36 GHz, the first intermediate frequency, and the first section 20 downconverts this frequency to the frequency, for example frequency f2, within the transmit/receive range of 0-1 0Hz required to be transmitted.

Thus, it can be seen that in use of the output/input stage of Figure 2 as a transmitter output stage, by applying the modulation to oscillator 27 and retuning oscillator 27 to the first intermediate frequency of 1.36 GHz, the requirement for an additional oscillator for use only in the transmission mode of operation, viz. the oscillator 9 of the known output/input stage of Figure 1, is obviated.

Referring also to Figure 3, if, in the transmit mode of operation, the lack of isolation resulting in signal leak in the mixer 23 of Figure 2 is not sufficient to produce the required signal level for the signal of frequency 1.36 GHz, this level may be increased by, as shown in Figure 3, routing a fraction of the oscillator 27 output signal directly to the output of mixer 23.

Such routing is achieved by connection 33, which connection 33 includes a resistor 35 and switch 37, which switch 37 is closed in transmit mode and open in receive mode.

Referring also to Figure 4, in the transmit mode of operation, oscillator 27 may be disconnected from the input to mixer 23 to which it is connected in receive mode, and connected directly to the output of mixer 23. Such disconnection is achieved by switch 39. Such direct connection is achieved by way of connection 41, which connection 41 includes a switch 43. In the receive mode switch 43 is open and switch 39 closed. In the transmit mode switch 43 is closed and switch 39 open.

The transmitter/receiver output/input stage of Figure 2 may include one or more further sections to the right of filter 31, each further section comprising a mixer, oscillator, and filter. In use as a receiver input stage each further section provides downconversion to a further intermediate frequency. In use as a transmitter output stage, the oscillator 27 or any one of the oscillators of the one or more further sections is returned, this oscillator being retuned to the intermediate frequency provided by the section next farthest to the right than the section including the retuned oscillator. The modulation is applied to the retuned oscillator.

Claims (8)

1. A transmitter/receiver output/input stage comprising first and second mixers and first and second oscillators the second of which is a variable frequency oscillator, as a receiver input stage said first mixer mixing a signal received thereby with a signal generated by said first oscillator thereby to provide a first signal to said second mixer, said second mixer mixing said first signal with a signal generated by said second oscillator to provide an output signal of the receiver input stage of a predetermined frequency, as a transmitter output stage said second oscillator being retuned to the frequency of said first signal thereby to provide to said first mixer a second signal, said first mixer mixing said second signal with said signal generated by said first oscillator to provide an output signal of the transmitter output stage of the frequency of said signal received by said first mixer in the use as a receiver input stage.

2. An output/input stage according to Claim 1 wherein: said first oscillator is a variable frequency oscillator such that said output/input stage is usable over a range of transmit and receive frequencies; the mixing by said first mixer in the use as a receiver input stage upconverts the frequency in said range received by the first mixer to a frequency greater than the highest frequency in said range; and the mixing by said second mixer in the use as a receiver input stage downconverts the frequency of said first signal.

3. An output/input stage according to Claim 1 or Claim 2 wherein in the use as a transmitter output stage the signal generated by the retuned second oscillator is fed to said second mixer.

4. An output/input stage according to Claim 3 wherein in the use as a transmitter output stage a fraction of the signal generated by the retuned second oscillator is fed to the output of said second mixer by a direct connection between the oscillator and the output of the second mixer, which direct connection includes a resistor and a switch, which switch is open in the use as a receiver input stage and closed in the use as a transmitter output stage.

5. An output/input stage according to Claim 1 or Claim 2 wherein in the use as a transmitter output stage the signal generated by the retuned second oscillator is fed to the output of said second mixer by a direct connection between the oscillator and the output of the second mixer, which direct connection includes a switch, said output/input stage further including a further switch at the input to said second mixer from said second oscillator, in the use as a receiver input stage said first mentioned switch being open and said further switch being closed, in the use as a transmitter output stage said first mentioned switch being closed and said further switch being open.

6. An output/input stage according to any one of the preceding claims further including: a first bandpass filter for filtering the output of said first mixer in the use as a receiver input stage; and a second bandpass filter for filtering the output of said second mixer in the use as a receiver input stage.

7. An output/input stage according to any one of the preceding claims wherein in the use as a receiver input stage the signal received by said first mixer is a modulated signal and in the use as a transmitter output stage the signal generated by the retuned oscillator is a modulated signal.

8. A transmitter/receiver output/input stage substantially as hereinbefore described with reference to Figures 2, 3 and 4 of the accompanying drawings.