BACKGROUND

[0001] Analog-to-digital converters, such as flash and folding, use amplifier arrays to parallel process an input value. Interpolation can be used to generate intermediate values between two adjacent amplifiers in the array. For example, in a folding ADC architecture, folding can be used to reduce component count (such as the number of comparators), and the folded amplifier array output can be interpolated to recover resolution.

[0002] Resistive interpolation uses two or more resistors between adjacent amplifiers to provide one or more interpolation (intermediate) values between the amplifier-driven outputs. FIG. 1A illustrates a portion of a two-stage cascaded resistor interpolator, providing interpolation-by-3. The schematic can represent single-ended signals, or polarities of differential signals.

[0003] Stage N amplifiers Al and A2 drive nodes Dl and D2, with the series-coupled interpolation resistors R/R'/R providing intermediate interpolation nodes II and 12. The interpolation resistors need not be of the same resistance value, as indicated by R and R' .

[0004] The Stage N amplifier-driven nodes D1/D2 and interpolation nodes 11/12 provide the Stage N driven and interpolated outputs. The Stage N outputs are inputs to the Stage N+1 amplifiers at driven nodes, with interpolated nodes in between.

[0005] FIG. IB illustrates voltage inputs for amplifiers Al and A2, V _IN,I and V _IN,2 , and the resulting outputs: driven outputs VOU _T,DI and VOU _T,D2 from the driven nodes Dl and D2; and interpolation (intermediate) outputs VOU _T,II and VOU _T,I2 from the interpolated nodes II and 12. The interpolated voltages VOU _T,II and VOU _T,I2 have values intermediate the amplifier outputs

[0006] FIG. 1C illustrates the two-stage resistor interpolator with the stage nodes aligned (and numbered). As configured, a Stage N amplifier/node A6/6 drives the corresponding Stage N+1 amplifier/node A6/6 with a driven output, and the adjacent Stage N interpolation nodes 5 and 7 drive the Stage N+1 amplifier/nodes A3/3 and A9/9 with interpolated outputs, with interpolation resistors/nodes between the driven nodes. SUMMARY

[0007] In described examples, an amplifier array includes an amplifier stage connected to a resistor interpolator. The amplifier stage includes M amplifiers (M>2). The resistor interpolator is configured to provide an interpolation order N (N>2), and includes an input row and at least a second row, each row comprising multiple interpolation resistors connected in series at nodes. The input row includes M driven nodes connected to a respective amplifier, and (N-l) interpolation nodes intermediate each of adjacent driven nodes. The input row is connected in parallel to the second row, with at least some of the interpolation nodes of the first row connected to corresponding interpolation nodes of the second row. The resistor interpolator including at least one multi-row interpolation cell, comprising: in the input row, a driven node connected to first and second interpolation resistors connected between the driven node and respective adjacent first and second interpolation nodes; and in the second row, third and fourth interpolation resistors connected between respective third and fourth interpolation nodes and an intermediate fifth interpolation node; and with the first and second interpolation nodes of the input row connected respectively to the third and fourth interpolation nodes of the second row.

[0008] In other described examples, a circuit for analog-to-digital conversion includes at least one folding interpolated amplifier array with a folding amplifier stage, and a resistive interpolation stage. The folding amplifier stage includes M amplifiers (M>4), each coupled to the input terminal to receive the input value, the M amplifiers configured with a folding factor of N (N>2) to provide M/N amplifier stage outputs. A resistor interpolator is coupled to receive the M/N amplifier stage outputs, and is configured to provide an interpolation order N (N>2), and includes an input row and at least a second row, each row comprising multiple interpolation resistors connected in series at nodes. The input row includes M/N driven nodes connected to a respective amplifier, and (N-l) interpolation nodes intermediate each of adjacent driven nodes. The input row is connected in parallel to the second row, with at least some of the interpolation nodes of the first row connected to corresponding interpolation nodes of the second row. The resistor interpolator including at least one multi-row interpolation cell, including: in the input row, a driven node connected to first and second interpolation resistors connected between the driven node and respective adjacent first and second interpolation nodes; and in the second row, third and fourth interpolation resistors connected between respective third and fourth interpolation nodes and an intermediate fifth interpolation node; and with the first and second interpolation nodes of the input row connected respectively to the third and fourth interpolation nodes of the second row.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIGS. 1A, IB, 1C illustrate resistive interpolation: FIG. 1A illustrates a portion of a two-stage resistor interpolator configured for interpolation-by-three with three interpolation resistors [R/R'/R] and two interpolation nodes, with Stage N including amplifier-driven nodes [Al/Dl, A2/D2] and intermediate interpolation nodes [II, 12], which together drive Stage N+1 amplifiers; FIG. IB illustrates amplifier input voltages [A1/V _I N _{, I} , A2/V ₁ N, ₂ ], and resulting driven voltage outputs [VOUT,DI, VOUT,D2], and interpolation (intermediate) voltage outputs [VOUT,II, OU _T . _E ]; and FIG. 1C illustrates a portion of a two-stage resistor interpolator with the stage nodes aligned, including a Stage N driven amplifier/node [A6/6] that drives the corresponding Stage N+1 driven amplifier/node [A6/6], and adjacent Stage N interpolation nodes [5, 7] that drive the Stage N+1 amplifier/nodes [A3/3, A9/9] .

[0010] FIG. 2 illustrates an example amplifier array with multi-row resistive interpolation according to this description, including example cascaded multi-stage amplifier arrays [Stages N, N+1], each amplifier array including a multi-row resistor interpolator [100(N), 101/102; 100(N+1), 201/202], illustratively configured with interpolation order three, including multi-row interpolation cells [100(N), 106/109; 100(N+1), 203/206/209] in which an input-row driven node [106/106D] is not connected to a corresponding second/next-row node [106/1061], so that the non-driven node [106/1061] is an interpolation between adjacent interpolation nodes [106, 1051/1071].

[0011] FIG. 3 A illustrates an example folding ADC [200] including cascaded folding amplifier array stages [210], and including an example stage 1 folding interpolated amplifier array [250], with a folding amplifier stage [260], and a resistor interpolator stage [270] that is configured according to this description for multi-row resistive interpolation with multi-row interpolation cells.

[0012] FIG. 3B illustrates an example folding interpolated amplifier array [250], such as implemented in the folding ADC of FIG. 3 A, the amplifier array including an example folding amplifier stage with amplifier inputs A1-A9 and configured for folding-by-3 [A1/A4/A7, A2/A5/A8, A3/A6/A9] to provide folded amplifier outputs [FA1, FA2, FA3], which are interpolated by an example interpolation-by-3 multi-row resistor interpolator stage [270, 100] to provide amplifier array outputs VOU _T,I - VOU _T,9 (corresponding to the A1-A9 amplifier inputs), which are all interpolated according to this description.

[0013] FIG. 4 illustrates an example RF Sampling ADC [300] with dual folding ADCs [200A, 200B], which can be implemented as in FIGS. 3A/3B, including with folding interpolated amplifier arrays [FIGS. 3A/3B, 250], configured according to this description for multi-row resistive interpolation [FIG. 3B, 270, 100] with multi-row interpolation cells implemented as in FIG. 2.

DETAILED DESCRIPTION OF EXAMPLE EMB ODFMENT S

[0014] Described examples include an amplifier array with multi-row resistive interpolation, and design examples (example implementations).

[0015] In this description, an array of amplifiers means M amplifiers (M>2) that parallel process an input value. Interpolation-by-N means interpolation to generate (N-l) intermediate values between two adjacent amplifiers in an array, so as to increase the number of output values in the array from M driven outputs to M x N total outputs (for closed loop interpolation). Cascading amplifier arrays means placing two or more amplifier arrays in sequence, and using the output of one amplifier array to drive the input to a next amplifier array.

[0016] In brief overview, an amplifier array including an amplifier stage with M amplifiers (M>2), connected to a resistor interpolator (interpolation order N>2) including an input row and at least a second row, each row comprising interpolation resistors connected in series at nodes. The input row including M driven nodes connected to a respective amplifier, and connected in parallel to the second row, with at least some first-row interpolation nodes connected to corresponding second-row interpolation nodes. The resistor interpolator comprises at least one multi-row interpolation cell, with: in the input row, a driven node coupled through first and second interpolation resistors to respective adjacent first and second interpolation nodes; and in the second row, third and fourth interpolation nodes coupled through third and fourth interpolation resistors to an intermediate fifth interpolation node; and with the first and second interpolation nodes connected respectively to the third and fourth interpolation nodes. Multi-row resistive interpolation with multi-row interpolation cells according to this description increases interpolation linearity by increasing uniformity in gain and impedance between output interpolation nodes.

[0017] FIG. 2 illustrates an example amplifier array with multi-row resistive interpolation according to this description. The amplifier array is implemented in an example cascade 100 of amplifier arrays represented by portions of Stage N and Stage N+1 amplifier arrays.

[0018] Each of the Stage N and N+1 amplifier arrays includes an amplifier stage, and a multi-row resistor interpolator stage.

[0019] The example Stage N amplifier stage is illustrated with amplifiers A6, and A9, interconnected to an associated multi-row resistor interpolator stage 100(N) as shown, and as described hereinbelow. The example Stage N+1 amplifier stage is illustrated with amplifiers A3, A6 and A9, interconnected to an associated multi-row resistor interpolator stage 100(N+1) as shown, and as described hereinbelow.

[0020] The example resistor interpolators 100(N) and 100(N+1) are illustrated with two parallel-connected interpolator rows 101/102 and 201/202, with interconnect as shown, and as described hereinbelow. Interpolator rows 101 and 201 are designated as input rows, and interpolator rows 102 and 202 are designated as second (next) rows. The example Stage N and N+1 resistor interpolators are illustratively configured for interpolation-by-3 (interpolation order three).

[0021] The Stage N amplifiers A6, A9 are connected to the input row 101 of the example resistor interpolator 100(N), driving inputs to nodes 6, and 9. The Stage N+1 amplifiers A3, A6, A9 are connected to the input row 201 of the example resistor interpolator 100(N+1), driving inputs to nodes 3, 6, and 9. For the example resistor interpolators 100(N) and 100(N+1), the second rows 102 and 202 provide the outputs for the associated amplifier array. According to aspects of this description hereinbelow, all of the amplifier array outputs are interpolated.

[0022] The amplifier arrays can represent a single-ended design, or one half of a differential design. The resistor interpolator can be implemented as an open loop or closed loop design. For an open loop configuration, the outside nodes are not interpolated, and will be driven nodes.

[0023] Each of the multi-row resistor interpolators 100(N) and 100(N+1) are configured with multi-row interpolation cells according to this description. Resistor interpolator 100(N) illustratively includes interpolation cells 106 and 109. Resistor interpolator 100(N+1) illustratively includes interpolation cells 203, 206 and 209.

[0024] Example interpolation cell 106 includes in the input row 101 a driven node 106D (node 6) driven by amplifier A6, and adjacent interpolation nodes 5 and 7. The input row interpolation nodes 5 and 7 of interpolation cell 106 adjacent driven node 106D are connected to corresponding interpolation nodes 1051 and 1071 of the second interpolation row 102.

[0025] According to aspects of this description, the driven node 106D of the input interpolation cell 106 is not connected to the corresponding node 1061 of the second interpolation row 102. As a result, node 1061 provides an interpolation between the adjacent interpolation nodes 1051 and 1071 of the interpolation cell 106. Accordingly, the outputs from interpolation cell 106 are all interpolation nodes, which are: 1061 and the adjacent interpolation nodes 1051 and 1071.

[0026] Stage N interpolation cell 106 in the resistor interpolator 100(N) provides inputs to the Stage N+l amplifier stage, amplifiers A3, A6, and A9 driving nodes 3, 6, and 9. Stage N interpolation node 1061 provides input to amplifier A6 driving node 206D in the input row 201 for the Stage N+l resistor interpolator 100(N+1), within an interpolation cell 206. Stage N interpolation nodes 1051 and 1071 provide input to amplifiers A3 and A9 driving nodes 203D and 209D of the of the Stage N+l input row 201 of the resistor interpolator 100(N+1), within interpolation cells 203 and 209.

[0027] The interconnect and functionality of interpolation cells 203, 206 and 209 are identical to that of the described interpolation cell 106. For example, the input row 201 driven nodes 203D, 206D, 209D are not connected to the corresponding nodes 2031, 2061, 2091 of the second row 202. As a result, as with the interpolation cell 106, the outputs from these cells are all interpolations based on the adjacent interpolation nodes.

[0028] For the illustrated example cascaded amplifier array with multi-row resistive interpolation, using interpolation cells according to this description, the number of outputs increases due to interpolation. For example, interpolation cell 106 receives input from amplifier A6 at node 106D (input row 101), and provides three (interpolated) outputs from the second (next or output) row 102: 1061, and 1051/1071. As described further in connection with the folding interpolated ADC implementation illustrated in FIGS. 3A/3B, the amplifier stages can be implemented with folding, such as folding-by-3 to reduce the number of inputs 3X, followed by interpolation-by-3 provided by the multi-row resistive interpolation stages, so that the number of outputs is the same as the number of inputs, and the total parallel signals at each stage stays nearly constant.

[0029] An advantage of multi-row resistive interpolation with multi-row interpolation cells according to this description is to match the gain at driven and interpolated nodes, by not using the output of the amplifiers directly. Instead, the multi-row interpolation cell effectively replaces a higher-gain driven with an interpolation node by interpolating between the two adjacent interpolated nodes, which drops the gain to nearly a constant value for the output nodes. This interpolation cell design matches output impedance for the outputs (interpolated) of the resistor interpolator, improving matching of settling time and linearity. The improvement in linearity increases as stages are cascaded.

[0030] These advantages are even more significant for designs in which the amplifiers are open loop and therefore non-linear. As a result, the difference in gain between the driven nodes and the interpolated nodes becomes more pronounced, as the entire transfer curve becomes more non-linear.

[0031] The example amplifier array described in connection with FIG. 2 includes an example multi-row resistor interpolator with two interpolation rows (input and second). Additional interpolation rows can be used to increase gain uniformity between output nodes, and thereby increase linearity. Increasing the number of rows involves design trade-offs in terms of area, parasitic capacitance, power and speed.

[0032] FIG. 3A illustrates an example folding ADC 200 including cascaded folding amplifier array stages 210. Such a folding ADC design is described in US Patent 7,710,305 "Unified Architecture for Folding ADC", the disclosure of which is incorporated in its entirety.

[0033] A folding ADC 200 includes, in addition to folding amplifier array stages 210, associated distributed (fine) comparator stages 220, and an encoder 230. An example folding interpolated amplifier array 250 includes a folding amplifier stage 260, and a resistor interpolator stage 270. The resistor interpolator 270 can be configured according to this description for multi-row resistive interpolation with multi-row interpolation cells.

[0034] FIG. 3B illustrates an example design for the folding interpolated amplifier array 250 in FIG. 3A. Amplifier array 250 includes a folding amplifier stage 260 with amplifier inputs A1-A9. The folding amplifier stage 260 is configured for folding-by-3, with amplifiers A1/A4/A7 folded to provide a folded amplifier output FAl, amplifiers A2/A5/A8 folded to provide folded amplifier output FA2, and amplifiers A3/A6/A9 folded to provide folded amplifier output FA3.

[0035] The folded amplifier outputs FAl, FA2, FA3 are interpolated by an example interpolation-by-3 resistor interpolator stage 270. Resistor interpolator stage 270 includes a multi-row resistor interpolator design 100, such as described in connection with FIG. 2.

[0036] The example multi-row resistor interpolator 100 includes an input row 101, and a second (output) row 102. Input row 101 includes driven nodes connected to receive the folded amplifier outputs FA1-FA3. The resistor interpolator 100 provides amplifier array outputs VOU _T,I - VOU _T,9 , all of which are interpolated, i.e., output from interpolated nodes of the second (output) row 102 none of which are directly driven by the folded amplifier inputs FA1-FA3 to the resistor interpolator.

[0037] For example, resistor interpolator 100 includes interpolation cells (such as FIG. 2, 106) centered at VOU _T,2 , VOU _T, 5, and VOU _T, 8- Accordingly, these interpolation cell output nodes (such as FIG.2, 1061) are interpolated according to this description, eliminating directly driven nodes with lower impedance and different linearity.

[0038] As illustrated, the example resistor interpolator 100 implies a closed loop configuration because it interpolates two more values VOU _{T, I} and VOU _T, 9- However, the closed loop is not explicitly shown as a connection between the top and bottom of the resistor strings 101 and 102.

[0039] The folding amplifier stage 260 results in a 3X reduction between the number of amplifier inputs A1-A9, and folded amplifier outputs FA1-FA3 to the resistor interpolator stage 270. Interpolation in the resistor interpolation stage 270 offsets the reduction in resolution resulting from folding in the amplifier stage, providing a 3X-interpolation increase in the number of outputs based on the folded inputs FA1-FA3.

[0040] FIG. 4 illustrates an example RF Sampling ADC 300 with dual folding ADCs 200A, 200B, which can be implemented as in FIGS. 3A/3B, including with folding interpolated amplifier arrays, which can be configured according to this description for multi-row resistive interpolation with multi-row interpolation cells.

[0041] Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.