Gain Partitioning In A Receiver

GAIN PARTITIONING IN A RECEIVER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims benefit under 35 USC 1 19(e) of U.S. provisional application number 60/979024, filed October 10, 2007, entitled "A Technique For Optimizing Gain Partitioning In A Receiver", the content of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION [0002] A receiver system typically consists of a series of stages consisting of pre-selectivity gain and mixing, frequency selectivity (i.e. a filter) and post-selectivity gain and mixing. Conventional receivers either set a total system gain with a predetermined partition between pre- and post selectivity gain, or rely on a separate controller or demodulator to independently adjust pre and post selectivity gains to achieve the linearity/noise tradeoff.

[0003] Figure 1 is a simplified block diagram of a receiver 100, as known in the prior art. In receiver 100, amplifier 110 has a gain G] that provides pre-selectivity gain. Frequency converter 120, which may be a mixer, provides frequency conversion. Filter Di 130 is typically a bandpass filter adapted to filter out undesired signal. Amplifier 140 has a gain of G2 and provides post- selectivity gain. A local oscillator (not shown) is often used to provide an oscillating signal to frequency converter 120. Frequency converter 120, and filter 130 typically have finite linearity and thus it is desirable to limit the range of signals that are coupled to them.

[0004] Figure 2 A shows a spectrum of exemplary signals received by filter 130. The desired signal is shown as having the frequency Fd. The spectrum of the receives signals often includes undesired signal components (also referred to as blockers) shown as having frequencies FbI and Fb2 that interfere with the desired signal, causing non-linearity, distortion, etc. For example, the spacing and amplitude of the undesired signals Fb 1 and Fb2 may result in a third order intermodulation distortion product at the output of amplifier 110. As such, it is not desirable to place too much gain before filter 130 which is adapted to attenuate the blocker signals, as shown in Figure 2B. The reduction of the undesired signals enables amplifier 140 to amplify the desired frequencies in without substantially increasing the amplitudes of the undesired signals.

[0005] By reducing the gain Gl of amplifier 110, the linearity is improved. Reducing the gain of the first amplifier 1 10 also reduces the amplitude of signal Sl. To keep the amplitude of signal S4 constant, gain G2 may be increased. The gain redistribution between amplifiers 1 10 and 140 reduces distortion but also results in degradation of the signal-to-noise (SNR) ratio. Therefore a tradeoff exists between increasing the gain Gl to improve signal to noise ratio, and degrading linearity performance of the system (increasing the distortion products in the signal) when blockers are present. [0006] Gains Gi and G2 are typically selected such that the total gain G|*G2 is equal to a known value. In accordance with one conventional technique, for a given input signal level So, a predetermined gain partitioning of Gi and G2 is used. Figure 3 is a block diagram of a conventional receiver 300 configured to achieve a predetermined gain partitioning of Gi and G2 using control signal Tsys. Figure 4 shown plots of gains Gi, G2 and Gi*G2 (Gsys) for a receiver having predetermined gain partitions.

[0007] In receiver 300, the gains of the first and second amplifiers 110 and 140, respectively, are controlled by gain controller 310 that controls the gains Gi and G2 in accordance with an algorithm that provides fixed gain partitioning using signal Tsys. Figure 4 shows examples of the gain G) from amplifier 110, gain G2 from amplifier 140 as well as the products of these two gains. The attack point (AP) represents the signal level at which total gain Gsys begins to be fall. The take-over point (TOP) represents the signal level at which gain control is passed from signal T2 to signal Ti . The TOP and AP values are typically predetermined and fixed. In a typical television system, a demodulator is used to generate control signals Ti and T2.

[0008] In accordance with another conventional technique, the output signal of the second amplification stage is used to determine the gain partitioning. Figure 5 is a simplified block diagram of a receiver 500 having gain partitioning controlled by a demodulator 510. Demodulator 510 is configured to controls the values of Gi and G2 depending on the presence and level of blockers. Demodulator 510 operates to control the partitioning of the gain between amplifiers 110 and 140 by sensing the output signal S4 of second amplifier 140. Demodulator 510 may be programmed to estimate whether blockers or other undesired signal components are causing distortion in the desired signal. Demodulator 510 then repartitions the gain by adjusting signals Ti and T2.

BRIEF SUMMARY OF THE INVENTION [0009] 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.

[0010] In accordance with the present invention, for a given receiver path gain defined, for example, by the product of the pre and post selectivity gains, the present invention provides a self-contained, compact apparatus and method for adjusting the partitioning between pre and post-selectivity gain to optimize the signal level entering the filter disposed in the receiver. The receiver is thus enabled to continuously trade off linearity against noise depending on the presence or absence of undesired signals (blockers) at other frequencies without relying on the intervention of an external controller or demodulator.

[0011] A receiver, in accordance with one embodiment of the present invention includes, in part, a first amplification stage, a frequency conversion module responsive to the first amplification stage, a filter responsive to the frequency conversion module, a second amplification stage responsive to the filter, and a controller adapted to vary a gain of each of the first and second amplification stages in response to an output signal of the first amplification stage and further in response to an overall gain selected for the receiver.

[0012] A receiver in accordance with another embodiment of the present invention includes, in part, a first amplification stage, a frequency conversion module responsive to the fist amplification stage, a filter responsive to the frequency conversion module, and a second amplification stage responsive to the filter. The receiver is adapted to vary the gains of the first and second amplification stages in response to a first and second feedback signals. [0013] In one embodiment, the first and second feedback signals are supplied by a controller responsive to signals representative of the output signals of the first and second amplification stages. In one embodiment, the controller is external to the receiver. In one embodiment, the controller is further responsive to the filter. In one embodiment, the receiver includes a third amplification stage. In such embodiments, the controller is further responsive to a third signal representative of the output signal of the third amplification stage.

[0014] A method of controlling the gain of a receiver, in accordance with one embodiment of the present invention, includes, in part, amplifying a received signal to generate a first signal using a first amplification stage, frequency converting 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 and 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 receiver.

[0015] A method of controlling the gain of a receiver, in accordance with another embodiment of the present invention, includes, in part, amplifying a received signal to generate a first amplified signal using a first amplification stage, frequency converting 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 and second amplification stage in response to first and second feedback signals.

[0016] In one embodiment, the method further includes, in part, applying signals representative of the first and second amplified signals to a controller, and generating the first and second feedback signals in response to the signals applied to the controller. In one embodiment, the controller is external to the receiver. In one embodiment, the method further includes applying a signal representative of the filtered signal to the controller. In one embodiment, the controller is further responsive to a third amplified signal present in the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS [0017] Figure 1 is a simplified block diagram of a receiver, as known in the prior art. [0018] Figure 2A shows a spectrum of exemplary signals received by a filter disposed in a wireless communication receiver.

[0019] Figure 2B shows the filtering characteristics of a filter adapted to attenuate the undesired signals shown in Figure 2A.

[0020] Figure 3 is a simplified block diagram of a receiver, as known in the prior art.

[0021] Figure 4 is a simplified gain diagram of an embodiment of amplifier gains in a system having a predetermined gain partition.

[0022] Figure 5 is a block diagram of a receiver, as known in the prior art.

[0023] Figure 6 is a simplified block diagram of a receiver, in accordance with one exemplary embodiment of the present invention.

[0024] Figure 7 is a simplified block diagram of a receiver, in accordance with another exemplary embodiment of the present invention..

[0025] Figure 8A, 8B and 8C are examples of gain plots and gain partitioning for the receiver of Figure 7. [0026] Figure 9 is a flowchart of steps carried out to perform adaptive gain partitioning, in accordance with one embodiment of the present invention..

[0027] Figure 10 is a block diagram of a receiver, in accordance with one exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Figure 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 S 1 to determine the strength of the RF signal. Signal Sl 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 Tl and T2 that are respectively applied to amplifiers 1 10 and 140 to control their gains. As see from Figure 6, receiver 600 together with demodulator/controller 510 form a pair of control loops Ll and L2, which are independently controlled by the demodulator/controller 510. Loop Ll is used to control gain Gl via signal Tl, 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 1 10, and 140 using signals Tl and T2.

[0029] Figure 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 Tsys applied to controller 710 includes information about the overall gain of the two amplification stages. Signal Tsys may be supplied by, e.g., a demodulator. Accordingly in receiver 700, loop Ll is used to determine Gl. Controller 710 knowing the overall gain signal represented by signal Tsys sets the proper gain G2 using signal T2. The gain partitioning of receiver 700 automatically partitions the gains Gl 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 100 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.

[0030] Figure 8A, 8B and 8C illustrates an example of gain curves and gain partitioning for the variable gain partitioning receiver of Figure 7. Figure 8 A shows the characteristics of the overall gain Gsys of receiver 700. When signal Sl exceeds a certain reference level, TOP is reduced until Sl equals the reference or falls within a certain range of the desired reference, for example, to TOPi, as shown in Figure 8C. When Sl falls below the reference, TOP is increased until Sl once again equals the reference, for example, to TOP2, as shown in Figure 8B.

[0031] Referring to Figures 6 and 8, controller 710 operates in the following manner. Assume that the desired channel signal Sd is nearly constant, but blocker levels are fluctuating, causing total signal S1 to change. When sensor 610 detects that the total signal Si has exceeded an optimal reference level, loop L1 is used to reduce the TOP, effectively reducing G1 through Ti. G2 is increased through T2 to maintain a constant Gsys. Likewise, when sensor 610 detects that Si has dropped below the reference level, loop Li is used to increase the TOP, effectively increasing G i through Tj. G2 is decreased through T2, again maintaining constant Gsys. 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.

[0032] The receiver 700 of Figure 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.

[0033] 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 S 1 signal. A circuit implementing the method 900, such as the controller 710 of Figure 7, can compare the input Sl 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 S 1 signal is being updated.

[0034] Figure 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 Sl (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 Sl value is continuously updated or updated at a rate faster than the rate of the control loop. The controller receives the updated S 1 value.

[0035] At step 920 a determination is made as to whether the Sl 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 Sl 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.

[0036] If at step 930 the controller determines that S 1 is not less than the low reference level REFL, the controller instead proceeds to step 940 where the controller determines if S 1 is greater than the high reference level REFH. If not, the controller proceeds back to step 910 to await the next S 1 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.

[0037] Referring to step 920, if the controller determines that Sl is not substantially equal to the reference level, the controller proceeds to step 950 to determine if Sl is greater than the reference level. If so, 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 S 1 is not 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 Sl update.

[0038] 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.

[0039] 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.

[0040] Figure 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 Sl and S3. The overall gain of the receiver is defined by signal Tsys 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, S3 will reach a level where its distortion from filter D] and other baseband circuits will begin to affect the signal before the signal Si becomes the dominant source of distortion. The controller 710 can decide to reduce the gain Gi and compensate by increasing gain G2, thereby keeping S3 below a predetermined threshold. Other filters and gain control mechanisms can be introduced in the signal path and controlled in a similar manner.

[0041] 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.

WHAT IS CLAIMED IS:

1. A receiver comprising: a first amplification stage; a frequency conversion module responsive to the fist amplification stage; a filter responsive to the frequency conversion module; a second amplification stage responsive to said filter; and a controller adapted to vary a gain of each of the first and 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 receiver.

2. A receiver comprising: a first amplification stage; a frequency conversion module responsive to the fist amplification stage; a filter responsive to the frequency conversion module; a second amplification stage responsive to said filter; said receiver varying gains of the first and second amplification stages in response to a first and second feedback signals.

3. The receiver of claim 2 wherein said first and second feedback signals are supplied by a controller responsive to first and second signals representative of output signals of the first and second amplification stages.

4. The receiver of claim 3 wherein said controller is external to the receiver.

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

6. The receiver of claim 3 further comprising: a third amplification stage, said controller being further responsive to a third signal representative of output signals of the third amplification stage.

7. 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 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 and 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 receiver.

8. 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 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 and second amplification stage in response to first and second feedback signals.

9. The method of claim 8 further comprising: applying signals representative of the first and second amplified signals to a controller; and generating the first and second feedback signals in response to the signals applied to the controller.

10. The method of claim 9 wherein said controller is external to the receiver.

11. The method of claim 9 further comprising: applying a signal representative of the filtered signal to the controller.

12. The method of claim 9 wherein said controller being is further responsive to a third amplified signal present in the receiver.

13. A method of gain partitioning, the method comprising: determining a received signal metric at an intermediate point within a signal path; and adjusting a Take-Over-Point of a gain before the intermediate point relative to a gain following the intermediate point based on the received signal metric.

14. An apparatus for gain partitioning, the apparatus comprising: a comparator configured to compare a signal value against a predetermined reference level; and a gain controller configured to adjust an automatic gain control Take-Over-Point based at least in part on the comparison.

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