AD9865 Analog Devices, AD9865 Datasheet - Page 27

• Manufacturer Part Number: AD9865
• Description: 10-Bit Broadband Modem Mixed Signal Front End (MxFE®)
• Manufacturer: Analog Devices

Specifications of AD9865

• Resolution (bits): 10bit
• # Chan: 1
• Sample Rate: 80MSPS
• Interface: Par
• Analog Input Type: Diff-Uni
• Ain Range: 6.3 V p-p,8 mV p-p
• Adc Architecture: Pipelined
• Pkg Type: CSP

TXPGA CONTROL
The AD9865 also contains a digital PGA in the Tx path distri-
buted between the TxDAC and IAMP. The TxPGA is used to
control the peak current from the TxDAC and IAMP over a
7.5 dB and 19.5 dB span, respectively, with 0.5 dB resolution.
A 6-bit word is used to set the TxPGA attenuation according to
the mapping shown in Figure 58. The TxDAC gain mapping is
applicable only when Bit 0 of Register 0x0E is set, and only the
four LSBs of the 6-bit gain word are relevant.
–10
–11
–12
–13
–14
–15
–16
–17
–18
–19
–20
–1
–2
–3
–4
–5
–6
–7
–8
–9
0
0
Figure 58. Digital Gain Mapping of TxPGA
8
6-BIT DIGITAL CODE (Decimal Equivalent)
IAMPs IOUTN AND IOUTG
OUTPUTS HAS 19.5dB RANGE
16
24
32
TxDACs IOUTP OUTPUT
HAS 7.5dB RANGE
40
48
56
64
Rev. A | Page 27 of 48
The TxPGA register can be updated via the PGA[5:0] port or
SPI port. The first method should be considered for fast updates
of the TxPGA register. Its operation is similar to the description
in the RxPGA Control section. The SPI port allows direct up-
date and readback of the TxPGA register via Register 0x0A with
an update rate limited to 1.6 MSPS (SCLK = 32 MHz). Bit 6 of
Register 0x0A must be set for a read or write operation.
Table 17 lists the SPI registers pertaining to the TxPGA. The
TxPGA control register default setting is for minimum
attenuation (0 dBFS) with the PGA[5:0] port disabled for Tx
gain control.
Table 17. SPI Registers TxPGA Control
Address (Hex)
0x0A
0x0B
0x0E
Bit
(6)
(5:0)
(6)
(5)
(0)
Description
Enable TxPGA update via SPI
TxPGA gain code
Select TxPGA via PGA[5:0]
Select RxPGA via PGA[5:0]
TxDAC output (IAMP disabled)
AD9865