ZHCSF77A July   2016  – July 2016 LMH2832

PRODUCTION DATA.  

  1. 特性
  2. 应用
  3. 说明
  4. 修订历史记录
  5. Device Comparison Table
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements: SPI
    7. 7.7 Typical Characteristics
  8. Parameter Measurement Information
    1. 8.1 Setup Diagrams
    2. 8.2 ATE Testing and DC Measurements
    3. 8.3 Frequency Response
    4. 8.4 Distortion
    5. 8.5 Noise Figure
    6. 8.6 Pulse Response, Slew Rate, and Overdrive Recovery
    7. 8.7 Power-Down
    8. 8.8 Crosstalk, Gain Matching, and Phase Matching
    9. 8.9 Output Measurement Reference Points
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Analog Input Characteristics
      2. 9.3.2 Analog Output Characteristics
      3. 9.3.3 Driving Low Insertion-Loss Filters
      4. 9.3.4 Input Impedance Matching
      5. 9.3.5 Power-On Reset (POR)
    4. 9.4 Device Functional Modes
      1. 9.4.1 Power-Down (PD)
      2. 9.4.2 Gain Control
    5. 9.5 Programming
      1. 9.5.1 Details of the Serial Interface
      2. 9.5.2 Timing Diagrams
    6. 9.6 Register Maps
      1. 9.6.1 Register Descriptions
        1. 9.6.1.1 SW Reset Register (address = 2)
      2. 9.6.2 Power-Down Control Register (address = 3)
      3. 9.6.3 Channel A RW0 Register (address = 4)
      4. 9.6.4 Channel A RW1 Register (address = 5)
      5. 9.6.5 Channel B RW0 Register (address = 6)
      6. 9.6.6 Channel B RW1 Register (address = 7)
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Driving ADCs
        1. 10.1.1.1 SNR Considerations
        2. 10.1.1.2 SFDR Considerations
        3. 10.1.1.3 ADC Input Common-Mode Voltage Considerations (AC-Coupled Input)
        4. 10.1.1.4 ADC Input Common-Mode Voltage Considerations (DC-Coupled Input)
    2. 10.2 Typical Applications
      1. 10.2.1 DOCSIS 3.X Driver
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
          1. 10.2.1.2.1 Source Resistance Matching
          2. 10.2.1.2.2 Output Impedance Matching
          3. 10.2.1.2.3 Voltage Headroom Considerations
        3. 10.2.1.3 Application Curve
      2. 10.2.2 IQ Receiver
    3. 10.3 Do's and Don'ts
      1. 10.3.1 Do:
      2. 10.3.2 Don't:
  11. 11Power Supply Recommendations
    1. 11.1 Split Supplies
    2. 11.2 Supply Decoupling
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13器件和文档支持
    1. 13.1 器件支持
      1. 13.1.1 器件命名规则
    2. 13.2 文档支持
      1. 13.2.1 相关文档 
    3. 13.3 接收文档更新通知
    4. 13.4 社区资源
    5. 13.5 商标
    6. 13.6 静电放电警告
    7. 13.7 Glossary
  14. 14机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

9 Detailed Description

9.1 Overview

Each channel of the LMH2832 consists of an input attenuator block followed by a fully differential amplifier that has a gain of 30 dB. The attenuator has a range of 0 dB to –39 dB in 1-dB steps that is controlled by an SPI interface. The two channels can be controlled independently using the digital interface including power-down and bias settings. A separate analog power-down pin (PDA, PDB) is also included for each channel so that the device can bet set to a low-power state without waiting for a serial write to a register. The internal registers also include a power-on-reset (POR) that ensures the device starts in a known state after the power is reset.

9.2 Functional Block Diagram

LMH2832 alt_sbos709.gif

9.3 Feature Description

9.3.1 Analog Input Characteristics

The LMH2832 is a dual-channel device with two identical channels (A and B) that each have differential input pins (INP and INM) that denote the positive and negative inputs, respectively. The inputs are expected to be ac-coupled only, typically through a transformer or capacitor. The amplifier self-biases the input common-mode to mid-supply for the maximum input voltage range. The inputs of the LMH2832 can only be driven differentially. For single-ended input source applications, use a balun or fully differential amplifier (such as the LMH3401 or LMH5401) that can convert single-ended to differential signals before the LMH2832.

At maximum gain, the digital attenuator is set to 0 dB of attenuation, causing the input signal to be much larger than the output signal and forcing the maximum output voltage swing to be limited by the outputs of the device. However at minimum gain, the maximum voltage swing is limited by the inputs of the device because the attenuator causes the output voltage to be 9 dB lower than the input voltage. In minimum gain, the input voltage limits against the electrostatic discharge (ESD) devices before the output reaches the maximum swing limits. For linear operation, the input voltage must be kept within the maximum input voltage ratings described in the Electrical Characteristics table.

The input impedance of the LMH2832 is set by internal termination resistors to a nominal value of 150 Ω, differential. Process variations result in a range of values, as described in the Electrical Characteristics table. The input impedance is also affected by device parasitic effects at higher frequencies that cause the impedance to shift away from the nominal value.

9.3.2 Analog Output Characteristics

The LMH2832 has series, 10-Ω, on-chip resistors on each output to provide isolation from board parasitics that can cause instability. When designing a filter following the LMH2832, the filter source impedance calculation must include the two 10-Ω, on-chip resistors. Table 2 shows the calculated external source impedance values required for various matched filter loads.

Table 2. Output Resistor Values for Matched Loads

MATCHED FILTER IMPEDANCE (Ω) EXTERNAL SERIES RESISTOR PER OUTPUT (Ω)
100 80
150 130
200 180
300 280

9.3.3 Driving Low Insertion-Loss Filters

When driving high-speed ADCs, a filter is commonly driven with a matched impedance to the ADC. This impedance is matched by the amplifier by setting the combination of the output resistors to the same impedance as the ADC inputs. Impedance matching is often done to minimize any transmission reflections caused by the physical signal path. The drawback to using a matched impedance is that a voltage swing is required from the amplifier outputs that is twice the desired ADC input voltage swing, which can cause output voltage limitation issues.

To avoid using a matched impedance, a low insertion loss filter can be driven where there is little to no resistance added at the amplifier outputs. The amplifier outputs then only must swing to the value of the ADC full-scale input voltage, thus eliminating most of the potential amplifier output headroom issues. The requirements of this technique are that the amplifier must be able to provide enough current to the load of the ADC and that the path between the amplifier outputs and ADC inputs must be minimized to prevent any reflections.

9.3.4 Input Impedance Matching

The LMH2832 has a differential input impedance of 150 Ω that can be easily matched to single-ended, 50-Ω or 75-Ω systems using baluns. For a single-ended, 50-Ω input, a 1:3-Ω ratio balun can be used to create a 150-Ω differential source impedance to the device with a balun gain of 4.8 dB. For a single-ended, 75-Ω input, a 1:2-Ω ratio balun creates a 150-Ω differential source impedance to the device with a voltage gain of 3 dB.

9.3.5 Power-On Reset (POR)

The LMH2832 has a built-in, power-on-reset (POR) that sets the device registers to their default state (see the Register Maps section) on power-up. Note that the LMH2832 register information is lost when power is removed. When power is reapplied, the POR ensures that the device enters a default state. Power glitches (of sufficient duration) can also initiate the POR and return the device to a default state.

9.4 Device Functional Modes

9.4.1 Power-Down (PD)

The device supports power-down control using an external power-down (PDx) pin or by writing a logic high to bit 6 of SPI register 2h (see the Register Maps section). The external PDx pins are active high; when left floating, the device defaults to an on condition resulting from the internal pulldown resistors that cause a logic low on the PDx pins. The device PDx thresholds are noted in the Electrical Characteristics table. The device consumes approximately 7 mA in power-down mode. Note that the SPI register contents are preserved in power-down mode.

9.4.2 Gain Control

The LMH2832 gain can be controlled from 30-dB gain (0-dB attenuation) to –9-dB gain in 1-dB steps by digitally programming the SPI register 2h; see the Register Maps section for more details.

9.5 Programming

9.5.1 Details of the Serial Interface

The LMH2832 has a set of internal registers that can be accessed by the serial interface formed by the CS (serial interface enable), SCLK (serial interface clock), SDI (serial interface input data), and SDO (serial interface read-back data) pins. Serially shifting bits into the device is enabled when CS is low. SDI serial data are latched at every SCLK rising edge when CS is active (low). The serial data are loaded into the register at every 16th SCLK rising edge when CS is low. When the word length exceeds a multiple of 16 bits, the excess bits are ignored. Data can be loaded in multiples of 16-bit words within a single active CS pulse. The first eight bits form the register address and the remaining eight bits are the register data. The interface can function with SCLK frequencies from 25 MHz down to very low speeds (of a few hertz) and also with a non-50% SCLK duty cycle. A summary of the LMH2832 SPI protocol is:

  1. SPI-1.1 interface
  2. Independent channel A, B attenuation programming (6-bit gain control)
  3. SPI register contents are preserved in power-down mode
  4. SPI-controlled power modes (3-bit control for eight options to step down the power)
  5. Powered for the main 5-V power supply
  6. 1.8-V logic

9.5.2 Timing Diagrams

Figure 44 and Figure 45 show timing diagrams for the SPI write and read bus cycles, respectively. Figure 46 shows an example timing diagram for a streaming write cycle and Figure 47 shows an example timing diagram for a streaming read cycle. Figure 48, Figure 49, Figure 50, and Figure 51 illustrate timing diagrams and requirements for the clock, data input, data output, and chip select, respectively. See the Timing Requirements: SPI table for SPI timing requirements.

LMH2832 tim_spi_wr_bus_cycle_sbos709.gif Figure 44. SPI Write Bus Cycle Timing Diagram
LMH2832 tim_spi_rd_bus_cycle_sbos709.gif Figure 45. SPI Read Bus Cycle Timing Diagram
LMH2832 tim_spi_stream_wr_sbos709.gif Figure 46. SPI Streaming Write Example Timing Diagram
LMH2832 tim_spi_stream_rd_sbos709.gif Figure 47. SPI Streaming Read Example Timing Diagram
LMH2832 tim_spi_clock_sbos709.gif Figure 48. SPI Clock Timing Diagram
LMH2832 tim_spi_data_sbos709.gif Figure 49. SPI Data Input Timing Diagram
LMH2832 tim_spi_data_out_sbos709.gif Figure 50. SPI Data Output Timing Diagrams
LMH2832 tim_spi_cs_sbos709.gif Figure 51. SPI Chip Select Timing Diagrams

9.6 Register Maps

Table 3 shows the SPI registers for the LMH2832.

Table 3. SPI Register Map

ADDRESS
(A[6:0])
R/W DEFAULT (Hex) REGISTER NAME REGISTER DATA
7 6 5 4 3 2 1 0
0 R B3 Revision ID 1 0 1 1 0 0 1 1
1 R 23 Product ID 0 0 1 0 0 0 1 1
2 R/W 00 SW reset Reserved Reset B Reserved Reset A
3 R/W 00 Power-down Reserved PD B Reserved PD A
4 R/W 20 Channel A RW0, bias control Channel A RW0
5 R/W 14 Channel A RW1, attenuator control Channel A RW1
6 R/W 20 Channel B RW0, bias control Channel B RW0
7 R/W 14 Channel B RW1, attenuator control Channel B RW1
8-127 R 00 Reserved 0 0 0 0 0 0 0 0

9.6.1 Register Descriptions

Exercising the SW reset function returns all registers to the default values of the respective channel.

9.6.1.1 SW Reset Register (address = 2)

Figure 52. SW Reset Register
7 6 5 4 3 2 1 0
Reserved Reset B Reserved Reset A
R-0h R/W-0h R-0h R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 4. SW Reset Register Field Descriptions

Bit Field Type Reset Description
7-5 Reserved R 0h Reserved.
4 Reset B R/W 0h This bit is a self-clearing bit.
0 = No action
1 = Reset
3-1 Reserved R 0h Reserved.
0 Reset A R/W 0h This bit is a self-clearing bit.
0 = No action
1 = Reset

9.6.2 Power-Down Control Register (address = 3)

Figure 53. Power-Down Control Register
7 6 5 4 3 2 1 0
Reserved PD B Reserved PD A
R-0h R/W-0h R-0h R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 5. Power-Down Control Register Field Descriptions

Bit Field Type Reset Description
7-5 Reserved R 0h Reserved.
4 PD B R/W 0h 0 = Active
1 = PD
3-1 Reserved R 0h Reserved.
0 PD A R/W 0h 0 = Active
1 = PD

9.6.3 Channel A RW0 Register (address = 4)

Figure 54. Channel A RW0 Register
7 6 5 4 3 2 1 0
Channel A RW0
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 6. Channel A RW0 Register Field Descriptions

Bit Field Type Reset Description
7-0 Channel A RW0 R/W 0h These bits drive the output CHA_RW0[7:0] and are reset by a device reset or Reset A. Table 10 lists controls for this register.

9.6.4 Channel A RW1 Register (address = 5)

Figure 55. Channel A RW1 Register
7 6 5 4 3 2 1 0
Channel A RW1
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 7. Channel A RW1 Register Field Descriptions

Bit Field Type Reset Description
7-0 Channel A RW1 R/W 0h These bits drive the output CHA_RW1[7:0] and are reset by a device reset or Reset A. Table 11 lists controls for this register.

9.6.5 Channel B RW0 Register (address = 6)

Figure 56. Channel B RW0 Register
7 6 5 4 3 2 1 0
Channel B RW0
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 8. Channel B RW0 Register Field Descriptions

Bit Field Type Reset Description
7-0 Channel B RW0 R/W 0h These bits drive the output CHB_RW0[7:0] and are reset by a device reset or Reset B. Table 10 lists controls for this register.

9.6.6 Channel B RW1 Register (address = 7)

Figure 57. Channel B RW1 Register
7 6 5 4 3 2 1 0
Channel B RW1
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 9. Channel B RW1 Register Field Descriptions

Bit Field Type Reset Description
7-0 Channel B RW1 R/W 0h These bits drive the output CHB_RW1[7:0] and are reset by a device reset or Reset B. Table 11 lists controls for this register.

Table 10. Bias Control Register Bit Settings (Channels A, B)(1)

7 6 5 4 3 2 1 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1
0 0 0 0 0 0 1 X
0 0 0 0 0 1 X X
0 0 0 0 1 X X X
0 0 0 1 X X X X
0 0 1 X X X X X
0 1 X X X X X X
1 X X X X X X X
(1) Default value: 001xxxxx. Highest power: 1xxxxxxx. Lower power: 00000000.

Table 11. Attenuator Control Register Bit Settings (Channels A, B)(1)

7 6 5 4 3 2 1 0
Reserved, always read 0 0 0 0 0 0 0
Reserved, always read 0 0 0 0 0 0 1
Reserved, always read 0 0 0 0 0 1 0
Reserved, always read 0 0 0 0 0 1 1
Reserved, always read 0 0 0 0 1 0 0
Reserved, always read 0 0 0 0 1 0 1
Reserved, always read 0 0 0 0 1 1 0
Reserved, always read 0 0 0 0 1 1 1
Reserved, always read 0 0 0 1 0 0 0
Reserved, always read 0 0 0 1 0 0 1
Reserved, always read 0 0 0 1 0 1 0
Reserved, always read 0 0 0 1 0 1 1
Reserved, always read 0 0 0 1 1 0 0
Reserved, always read 0 0 0 1 1 0 1
Reserved, always read 0 0 0 1 1 1 0
Reserved, always read 0 0 0 1 1 1 1
Reserved, always read 0 0 1 0 0 0 0
Reserved, always read 0 0 1 0 0 0 1
Reserved, always read 0 0 1 0 0 1 0
Reserved, always read 0 0 1 0 0 1 1
Reserved, always read 0 0 1 0 1 0 0
Reserved, always read 0 0 1 0 1 0 1
Reserved, always read 0 0 1 0 1 1 0
Reserved, always read 0 0 1 0 1 1 1
Reserved, always read 0 0 1 1 0 0 0
Reserved, always read 0 0 1 1 0 0 1
Reserved, always read 0 0 1 1 0 1 0
Reserved, always read 0 0 1 1 0 1 1
Reserved, always read 0 0 1 1 1 0 0
Reserved, always read 0 0 1 1 1 0 1
Reserved, always read 0 0 1 1 1 1 0
Reserved, always read 0 0 1 1 1 1 1
Reserved, always read 0 1 0 0 0 0 0
Reserved, always read 0 1 0 0 0 0 1
Reserved, always read 0 1 0 0 0 1 0
Reserved, always read 0 1 0 0 0 1 1
Reserved, always read 0 1 0 0 1 0 0
Reserved, always read 0 1 0 0 1 0 1
Reserved, always read 0 1 0 0 1 1 0
Reserved, always read 0 1 0 0 1 1 1
(1) Default attenuation setting: xx001011. Maximum attenuation (lowest gain setting): xx100111. Minimum attenuation (highest gain setting): xx000000.