Gain partitioning in a receiver

Abstract

An automatic gain control loop disposed in a receiver is adapted to compensate for varying levels of out of band interference sources by adaptively controlling the gain distribution throughout the receive signal path. One or more intermediate received signal strength indicator (RSSI) detectors are used to determine a corresponding intermediate signal level. The output of each RSSI detector is coupled to an associated comparator that compares the intermediate RSSI value against a corresponding threshold. The take over point (TOP) for gain stages is adjusted based in part on the comparator output values. The TOP for each of a plurality of gain stages may be adjusted in discrete steps or continuously.

Claims

1. A receiver comprising: a first amplification stage; a frequency conversion circuit responsive to the first amplification stage; a filter responsive to the frequency conversion circuit; a second amplification stage responsive to said filter; and a controller adapted to vary a gain of each of the first amplification stage and the second amplification stage in response to an output signal of the first amplification stage and further in response to an input signal of the second amplification stage, wherein the output signal of the first amplification stage is received by the controller and is operably coupled to the frequency conversion circuit, and wherein the controller is operable to reduce the gain of the first amplification stage and increase the gain of the second amplification stage to maintain the input signal of the second amplification stage below a threshold.

2. A receiver comprising: a first amplification stage; a frequency conversion circuit responsive to the first amplification stage; a filter responsive to the frequency conversion circuit; and a second amplification stage responsive to said filter; said receiver varying gains of the first and second amplification stages in response to a first control signal and a second control signal, wherein an output signal of the first amplification stage is used to determine said first control signal and said second control signal, and wherein a controller is operable to reduce the gain of the first amplification stage and increase the gain of the second amplification stage to maintain an input signal of the second amplification stage below a threshold.

3. The receiver of claim 2, wherein said first control signal and said second control signal are supplied by the controller responsive to an overall gain selected for the first and second amplification stages.

4. The receiver of claim 3, wherein said controller is external to the first and second amplification stages.

5. The receiver of claim 3, wherein said controller is responsive to the filter.

6. A method of controlling a gain of a receiver, the method comprising: amplifying a received signal to generate a first signal using a first amplification stage; frequency converting, via a frequency conversion circuit, the first signal; filtering the frequency converted signal; amplifying the filtered signal to generate a second signal using a second amplification stage; and varying a gain of each of the first amplification stage and the second amplification stage in response to an output signal of the first amplification stage and further in response to an overall gain selected for the first and second amplification stages, wherein the output signal of the first amplification stage is received by a controller and the frequency conversion circuit, and wherein the gain of the first amplification stage is reduced and the gain of the second amplification stage is increased to maintain an input signal of the second amplification stage below a threshold.

7. A method of controlling a gain of a receiver, the method comprising: amplifying a received signal to generate a first amplified signal using a first amplification stage; frequency converting, via a frequency conversion circuit, the first amplified signal; filtering the frequency converted signal; amplifying the filtered signal to generate a second amplified signal using a second amplification stage; and varying a gain of each of the first amplification stage and the second amplification stage in response to a first control signal and a second control signal, wherein an output signal of the first amplification stage is used to determine said first control signal and said second control signal, and wherein the gain of the first amplification stage is reduced and the gain of the second amplification stage is increased thereby maintaining the filtered signal below a threshold.

8. The method of claim 7, further comprising: applying a signal representative of the first amplified signal to a controller; applying an overall gain signal to the controller; and generating said first control signal and said second control signal in response to the signal and the overall gain signal applied to the controller.

9. The method of claim 8, wherein said controller is external to the first and second amplification stages.

10. The method of claim 8, further comprising: applying a signal representative of the filtered signal to the controller; and generating said first control signal and said second control signal in response to the signal representative of the first amplified signal, the overall gain signal, and the signal representative of the filtered signal applied to the controller.

11. The method of claim 8, wherein said controller is operable to control a gain partitioning according to the first control signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a simplified block diagram of a receiver, as known in the prior art.

(2) FIG. 2A shows a spectrum of exemplary signals received by a filter disposed in a wireless communication receiver.

(3) FIG. 2B shows the filtering characteristics of a filter adapted to attenuate the undesired signals shown in FIG. 2A.

(4) FIG. 3 is a simplified block diagram of a receiver, as known in the prior art.

(5) FIG. 4 is a simplified gain diagram of an embodiment of amplifier gains in a system having a predetermined gain partition.

(6) FIG. 5 is a block diagram of a receiver, as known in the prior art.

(7) FIG. 6 is a simplified block diagram of a receiver, in accordance with one exemplary embodiment of the present invention.

(8) FIG. 7 is a simplified block diagram of a receiver, in accordance with another exemplary embodiment of the present invention.

(9) FIGS. 8A, 8B and 8C are examples of gain plots and gain partitioning for the receiver of FIG. 7.

(10) FIG. 9 is a flowchart of steps carried out to perform adaptive gain partitioning, in accordance with one embodiment of the present invention.

(11) FIG. 10 is a block diagram of a receiver, in accordance with one exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(12) FIG. 6 is a block diagram of a receiver 600, in accordance with one embodiment of the present invention. Receiver 600 is shown as including, in part, amplifiers 110, 140, frequency converter 120, filter 130 and sensor 610. A local oscillator (not shown) provides an oscillating signal to frequency converter 120. Frequency converter 120 may be a mixer, a multiplier, etc. Demodulator 510 may be external or internal to receiver 600. Sensor 610 sense signal S1 to determine the strength of the RF signal. Signal S1 so sensed is supplied to demodulator/controller 510. Also supplied to demodulator/controller 510 is signal S4 that is generated by amplifier 140. In response, demodulator/controller 510 generates signals T1 and T2 that are respectively applied to amplifiers 110 and 140 to control their gains. As see from FIG. 6, receiver 600 together with demodulator/controller 510 form a pair of control loops L1 and L2, which are independently controlled by the demodulator/controller 510. Loop L1 is used to control gain G1 via signal T1, and loop L2 is used to control gain G2 via signal T2. Demodulator/controller 510 may use any one of a number of different algorithms to vary the gains of amplifiers 110, and 140 using signals T1 and T2.

(13) FIG. 7 is a block diagram of a receiver 700, in accordance with another embodiment of the present invention. Receiver 700 is similar to receiver 600 except that in receiver 700 signal T.sub.sys applied to controller 710 includes information about the overall gain of the two amplification stages. Signal T.sub.sys may be supplied by, e.g., a demodulator. Accordingly in receiver 700, loop L1 is used to determine G1. Controller 710 knowing the overall gain signal represented by signal T.sub.sys sets the proper gain G2 using signal T2. The gain partitioning of receiver 700 automatically partitions the gains G1 and G2 to achieve a desired gain Gsys specified by controller 710 based on input from a single control line Tsys. Because only one control line Tsys is required in receiver 700, it is easy to implement. Furthermore, receiver 700 may be configured to adapt TOP to trade off linearity with signal to noise ratio depending on the level of blockers. Additionally, controller 710 may be exclusive of the demodulator and thus, controller 710 may be implemented on the same IC as the other elements of the receiver 700.

(14) FIGS. 8A, 8B and 8C illustrates an example of gain curves and gain partitioning for the variable gain partitioning receiver of FIG. 7. FIG. 8A shows the characteristics of the overall gain G.sub.sys of receiver 700. When signal S1 exceeds a certain reference level, TOP is reduced until S1 equals the reference or falls within a certain range of the desired reference, for example, to TOP.sub.1, as shown in FIG. 8C. When S1 falls below the reference, TOP is increased until S1 once again equals the reference, for example, to TOP.sub.2, as shown in FIG. 8B.

(15) Referring to FIGS. 7 and 8, controller 710 operates in the following manner. Assume that the desired channel signal S.sub.d is nearly constant, but blocker levels are fluctuating, causing total signal S.sub.1 to change. When sensor 610 detects that the total signal S.sub.1 has exceeded an optimal reference level, loop L.sub.1 is used to reduce the TOP, effectively reducing G.sub.1 through T.sub.1. G2 is increased through T.sub.2 to maintain a constant G.sub.sys. Likewise, when sensor 610 detects that S.sub.1 has dropped below the reference level, loop L.sub.1 is used to increase the TOP, effectively increasing G.sub.1 through T.sub.1. G2 is decreased through T.sub.2, again maintaining constant G.sub.sys. The optimal reference level varies from application to application and can be programmed dynamically as the application changes. Hysteresis may be used to stabilize the circuit in a digital implementation.

(16) The receiver 700 of FIG. 7 does not require an external controller or demodulator to optimize the gain partitioning, making the system very simple to interface with any demodulator, and any communication standard without the need for extensive software development.

(17) A practical digital implementation is presented in conjunction with the method 900 illustrated below. It provides discrete steps in TOP control and receives a digital S1 signal. A circuit implementing the method 900, such as the controller 710 of FIG. 7, can compare the input S1 level to a reference level and increase or decrease a digital word controlling the TOP to compensate. The controller circuit can be clocked at a rate that can depend on the rate that the S1 signal is being updated.

(18) FIG. 9 is a flowchart 900 of steps carried out to perform adaptive gain partitioning, in accordance with one embodiment of the present invention. The process begins at step 910 when S1 (i.e., the output signal of the first amplification stage) value after the first gain stage is updated or upon the next iteration of the control loop if the S1 value is continuously updated or updated at a rate faster than the rate of the control loop. The controller receives the updated S1 value.

(19) At step 920 a determination is made as to whether the S1 value is substantially the same as the predetermined reference level REF for the application that is presently active. If so, the controller proceeds to step 930 and determines if the S1 value is less than a predetermined low reference level REFL. If so, the controller proceeds to step 970 and increases the Take-Over-Point, up to a predetermined TOP limit.

(20) If at step 930 the controller determines that S1 is not less than the low reference level REFL, the controller instead proceeds to step 940 where the controller determines if S1 is greater than the high reference level REFH. If not, the controller proceeds back to step 910 to await the next S1 update without making any changes to the TOP. If, at step 940, the controller determines that the RSSI is greater than the high reference level REFH, the controller proceeds to step 960 to decrease the TOP down to a predetermined lower limit.

(21) Referring to step 920, if the controller determines that S1 is not substantially equal to the reference level, the controller proceeds to step 950 to determine if S1 is greater than the reference level. If not, the controller proceeds to step 970 to increase the TOP, but not to exceed the upper limit. If at step 950 the controller determines that S1 is greater than the reference level, the controller proceeds to step 960 to decrease the TOP but not smaller than a lower limit. The controller proceeds from either step 960 or step 970, that is, after adjusting the TOP, back to step 910 to await the next S1 update.

(22) It is understood that additional signal strength monitoring loops may be added in the signal path in order to detect which portion of the signal path is experiencing saturation first. Such capability may be useful for allowing the receiver to distinguish between blockers which are far from the desired signal or close to the desired signal.

(23) A close blocker is referred to as an N+/1 blocker or adjacent channel blocker (that is, a blocker which is one channel above or below the desired channel N). Blockers further away in frequency are similarly labeled. In many receivers, an N+/1 blocker may cause a portion of the signal path after mixing or filtering to limit receiver performance before the mixer saturates. A receiver is more susceptible to N+/1 blockers because the (undesirable) third-order distortion products from these blockers are more severe at frequencies closer to the blockers. To remedy these problems, in accordance with one embodiment of the present invention, an adaptive gain partitioning receiver includes sensors in the signal path to allow the receiver to distinguish between close in blockers, such as N+/1, from N+/2 and other blockers.

(24) FIG. 10 is a block diagram of a receiver 1000 that includes a pair of signal strength sensors. 810 and 820. Receiver 1000 is thus similar to receiver 700 except that receiver 1000 senses strength of signals S1 and S3. The overall gain of the receiver is defined by signal T.sub.sys applied to controller 710. Receiver 1000 thus detects when the weakest link in the signal path is being strained, and adjusts the gain partition(s) to relieve the strain on that link. In the N+/1 blocker case, S.sub.3 will reach a level where its distortion from filter D.sub.1 and other baseband circuits will begin to affect the signal before the signal S.sub.1 becomes the dominant source of distortion. The controller 710 can decide to reduce the gain G.sub.1 and compensate by increasing gain G.sub.2, thereby keeping S.sub.3 below a predetermined threshold. Other filters and gain control mechanisms can be introduced in the signal path and controlled in a similar manner.

(25) The above embodiments of the present invention are illustrative and not limiting. Various alternatives and equivalents are possible. The invention is not limited by the number of subbands disposed in the diversity receiver. The invention is not limited by the type of integrated circuit in which the present disclosure may be disposed. Nor is the disclosure limited to any specific type of process technology, e.g., CMOS, Bipolar, or BICMOS that may be used to manufacture the present disclosure. Other additions, subtractions or modifications are obvious in view of the present disclosure and are intended to fall within the scope of the appended claims.